tag:theconversation.com,2011:/id/topics/star-formation-7018/articlesStar formation – The Conversation2024-03-26T00:01:06Ztag:theconversation.com,2011:article/2263972024-03-26T00:01:06Z2024-03-26T00:01:06ZWe went looking for glowing interstellar gas – and stumbled on 49 unknown galaxies<figure><img src="https://images.theconversation.com/files/583996/original/file-20240325-28-68vtd0.jpg?ixlib=rb-1.1.0&rect=350%2C5%2C1514%2C1385&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Gas detected by MeerKAT (white contours) on top of a three-colour optical image from the DECaLS DR10 survey.</span> <span class="attribution"><a class="source" href="https://academic.oup.com/MNRAS/article-lookup/doi/10.1093/mnras/stae684">Glowacki et al. 2024.</a></span></figcaption></figure><p>Stars are born from huge clouds of mostly hydrogen gas floating in space. Astronomers like me study this gas because it helps us understand how stars and galaxies form and grow.</p>
<p>Hydrogen gas gives off a faint glow that is invisible to human eyes but can be observed with a telescope tuned to detect radio waves. </p>
<p>Recently, my colleagues and I were using a telescope like this – a radio telescope called MeerKAT, in South Africa – to look for hydrogen gas in a particular galaxy. We were only observing for less than three hours, which is quite a short amount of time since the hydrogen glow is so faint. </p>
<p>When we looked at the results, we were in for a huge surprise. Instead of discovering hydrogen gas in the galaxy we aimed at, we spotted it in no less than 49 previously unknown galaxies. Our findings are <a href="https://academic.oup.com/MNRAS/article-lookup/doi/10.1093/mnras/stae684">published</a> in the Monthly Notices of the Royal Astronomical Society.</p>
<h2>Gas in galaxies</h2>
<p>The giant clouds of gas in which stars are born are called nebulae. When stars eventually die, they expel their gas into their surrounding environment, where it eventually cools and forms new nebulae. </p>
<p>Galaxies are like huge factories where the life cycle of stars repeats itself over and over. To properly understand galaxies and how they grow and evolve, astronomers need to consider both the stars and the gas making up the galaxy. </p>
<p>One thing we are particularly interested in is “merger events”, when two galaxies collide and merge into a single, larger galaxy. These events can also impact the gas, and kickstart star formation. </p>
<p>Studying gas can often help us understand a galaxy’s history. Gas often extends far further out than the stars in galaxies. </p>
<p>When we see trails of disturbed gas, it is a classic clue that a recent galaxy merger or interaction has occurred. </p>
<p>But we don’t see galactic gas easily with optical telescopes. Thankfully, radio telescopes are a great tool for finding hydrogen gas.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/583828/original/file-20240323-30-pmfayi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of several large white radio dishes standing in a field." src="https://images.theconversation.com/files/583828/original/file-20240323-30-pmfayi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/583828/original/file-20240323-30-pmfayi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=324&fit=crop&dpr=1 600w, https://images.theconversation.com/files/583828/original/file-20240323-30-pmfayi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=324&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/583828/original/file-20240323-30-pmfayi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=324&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/583828/original/file-20240323-30-pmfayi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=408&fit=crop&dpr=1 754w, https://images.theconversation.com/files/583828/original/file-20240323-30-pmfayi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=408&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/583828/original/file-20240323-30-pmfayi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=408&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The MeerKAT radio telescope, made up of 64 radio dishes working together to act as a larger telescope.</span>
<span class="attribution"><span class="source">South African Radio Astronomy Observatory (SARAO)</span></span>
</figcaption>
</figure>
<h2>The MeerKAT radio telescope</h2>
<p>The MeerKAT radio telescope in South Africa <a href="https://www.sarao.ac.za/news/sarao-hosts-meerkat-5-years-conference-in-2024/">recently celebrated its fifth birthday</a>. It is one of the “pathfinder” telescopes for the much larger Square Kilometre Array (SKA), a project under construction in South Africa and Australia. </p>
<p>MeerKAT has already achieved some great results, <a href="https://academic.oup.com/mnras/article/501/3/3833/6034001">from detecting giant radio galaxies</a> to studying the <a href="https://www.sarao.ac.za/media-releases/new-meerkat-radio-image-reveals-complex-heart-of-the-milky-way/">centre of our own galaxy</a>, the Milky Way.</p>
<p>There are large survey projects underway with MeerKAT to study the star-forming hydrogen gas in galaxies. These include the <a href="https://www.aanda.org/articles/aa/full_html/2021/02/aa39655-20/aa39655-20.html">MIGHTEE-HI</a> and <a href="https://science.uct.ac.za/laduma">LADUMA</a> surveys, the latter of which will use MeerKAT for more than 3,000 hours searching one part of the sky for hydrogen gas in very distant galaxies. These surveys are specifically focused on finding hydrogen gas and are carefully planned and carried out with that goal in mind.</p>
<p>But that’s not the only way MeerKAT can be used. Astronomers can also pitch ideas for “open time” observations to tackle other science questions or goals. </p>
<p>That’s how this discovery came about. I was hoping to detect hydrogen gas in one specific galaxy with MeerKAT, as it is the most sensitive telescope for these studies. </p>
<p>We did not find hydrogen gas in that galaxy, which was fine. We astronomers don’t always find what we are looking for.</p>
<p>But when I inspected the MeerKAT data, I spotted some gas located away from the target galaxy. So we investigated further. </p>
<p>By using techniques developed for the larger MeerKAT science surveys such as LADUMA, we found a lot more gas. In total, we had 49 detections.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/583822/original/file-20240323-16-unrb75.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of a field of stars with small loops of coloured lines." src="https://images.theconversation.com/files/583822/original/file-20240323-16-unrb75.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/583822/original/file-20240323-16-unrb75.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=587&fit=crop&dpr=1 600w, https://images.theconversation.com/files/583822/original/file-20240323-16-unrb75.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=587&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/583822/original/file-20240323-16-unrb75.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=587&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/583822/original/file-20240323-16-unrb75.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=738&fit=crop&dpr=1 754w, https://images.theconversation.com/files/583822/original/file-20240323-16-unrb75.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=738&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/583822/original/file-20240323-16-unrb75.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=738&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The 49 new gas-rich galaxies detected by the MeerKAT radio telescope in South Africa. Each detection is shown as coloured contours, with redder colours indicating more distant gas from us, and bluer colours as closer gas. The background image comes from the optical PanSTARRS survey.</span>
<span class="attribution"><a class="source" href="https://academic.oup.com/MNRAS/article-lookup/doi/10.1093/mnras/stae684">Glowacki et al. 2024</a></span>
</figcaption>
</figure>
<h2>Meet the 49ers</h2>
<p>Each detection of the gas in these galaxies was brand new. In little more than two hours of observing time, MeerKAT had revealed several collections of neighbouring galaxies. </p>
<p>Some of these neighbours are even interacting with each other, as their gas content shows. This was not at all obvious from just looking at the optical images of their stars. </p>
<p>In one case, a galaxy is stealing gas from two companion galaxies, and using it to fuel its own star formation.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/583826/original/file-20240323-16-g8ybij.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/583826/original/file-20240323-16-g8ybij.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/583826/original/file-20240323-16-g8ybij.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=549&fit=crop&dpr=1 600w, https://images.theconversation.com/files/583826/original/file-20240323-16-g8ybij.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=549&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/583826/original/file-20240323-16-g8ybij.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=549&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/583826/original/file-20240323-16-g8ybij.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=689&fit=crop&dpr=1 754w, https://images.theconversation.com/files/583826/original/file-20240323-16-g8ybij.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=689&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/583826/original/file-20240323-16-g8ybij.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=689&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Examples of individual detections of the gas detected by MeerKAT (white contours) on top of a three-colour optical image from the DECaLS DR10 survey. The gas seen here extends further out than the stars in the galaxies.</span>
<span class="attribution"><a class="source" href="https://academic.oup.com/MNRAS/article-lookup/doi/10.1093/mnras/stae684">Glowacki et al. 2024</a></span>
</figcaption>
</figure>
<p>I’ve informally nicknamed this collection of galaxies the 49ers, <a href="https://www.loc.gov/collections/california-first-person-narratives/articles-and-essays/early-california-history/forty-niners/">a reference to the miners of the 1849 California gold rush</a>. </p>
<p>While MeerKAT took the observations containing the 49 gold nuggets in just a couple of hours, winnowing them out required several other tools. These included <a href="https://www.ilifu.ac.za/about/">the ilifu cloud supercomputer</a>, where we reduced the MeerKAT observations (“data reduction” is a kind of pre-processing that makes the raw observations useful) and a data visualisation tool called <a href="https://cartavis.org/">CARTA</a> which we used for the initial discovery of the 49 new galaxies.</p>
<p>We also examined our data with <a href="https://idavie.readthedocs.io/">iDaVIE-v, a virtual reality software for viewing astronomical datasets in 3D</a>. This software has already been <a href="https://theconversation.com/astronomers-have-discovered-a-rare-polar-ring-galaxy-wrapped-in-a-huge-ribbon-of-hydrogen-213254">used for new discoveries such as polar ring galaxies</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/T_AJlFeoRu0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">VR view of several “49er” gas-rich galaxies.</span></figcaption>
</figure>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/lNuWz_EB9ls?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">VR view of a zoom-in of the 49er galaxies.</span></figcaption>
</figure>
<h2>More gold nuggets to be found</h2>
<p>Finding 49 new galaxies in such a short amount of observation time is quite unusual, even with a telescope as powerful as MeerKAT. However, we know there are more galaxies waiting to be found in upcoming and existing MeerKAT observations. </p>
<p>In some other recent work, our team found traces of gas in more than 80 galaxies (most brand new) across three separate MeerKAT observations. Each of these observations was originally focused on a single galaxy, like the “open time” observation in which we found the 49ers. </p>
<p>What will we find next? We don’t know, but with MeerKAT – and eventually its more powerful successor, the SKA telescope – we’re confident astronomers will turn up plenty more pieces of gold.</p><img src="https://counter.theconversation.com/content/226397/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marcin Glowacki does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>An attempt to study gas in one galaxy with the MeerKAT radio telescope detected 49 other galaxies instead.Marcin Glowacki, Research Associate, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2035572023-05-24T21:06:10Z2023-05-24T21:06:10ZAstronomers detected two major targets with a single telescope – a mysterious signal and its source galaxy<figure><img src="https://images.theconversation.com/files/521206/original/file-20230417-28-c0lcs2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">ASKAP multiple landscape backview.</span> <span class="attribution"><span class="source">CSIRO</span></span></figcaption></figure><p>Astronomers have been working to better understand the galactic environments of fast radio bursts (FRBs) – intense, momentary bursts of energy occurring in mere milliseconds and with unknown cosmic origins.</p>
<p>Now, a study of the slow-moving, star-forming gas in the same galaxy found to host an FRB <a href="https://doi.org/10.3847/1538-4357/acc1e3">has been published in The Astrophysical Journal</a>. This is only the fourth-ever publication on two completely different areas of astronomy describing the same galaxy. </p>
<p>Even more remarkable is the fact that a single telescope made the discovery possible – from the same observation. </p>
<h2>Fast radio mysteries</h2>
<p>FRBs, first detected in 2007, are incredibly powerful pulses of radio waves. They originate from distant galaxies, and the signal typically only lasts a few milliseconds.</p>
<p>FRBs are immensely useful for studying the cosmos, from investigating <a href="https://news.ucsc.edu/2020/05/missing-matter.html">the matter that makes up the universe</a>, to even using them <a href="https://academic.oup.com/mnras/article-abstract/516/4/4862/6694260">to constrain the Hubble constant</a> – the measure of how much the universe is expanding.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-brief-history-what-we-know-so-far-about-fast-radio-bursts-across-the-universe-154381">A brief history: what we know so far about fast radio bursts across the universe</a>
</strong>
</em>
</p>
<hr>
<p>However, the origin of FRBs is an ongoing puzzle for astronomers. Some FRBs are known to repeat, <a href="https://iopscience.iop.org/article/10.1088/1674-1056/aca7ed">sometimes over a thousand times</a>. Others have only been detected once.</p>
<p>Whether these repeating or non-repeating signals have formed differently <a href="https://academic.oup.com/mnras/article-abstract/500/3/3275/5944128">is currently being investigated by several research groups</a>. At one point, we had more theories on how fast radio bursts are made than detections of them.</p>
<p>It’s an exciting time to be studying FRBs, as showcased by the recent study <a href="https://theconversation.com/for-the-first-time-astronomers-have-linked-a-mysterious-fast-radio-burst-with-gravitational-waves-202341">associating an FRB with a gravitational wave</a>. If that finding holds true, it means at least some FRBs could be created by two neutron stars merging to form a black hole. </p>
<p>However, it is hard to pinpoint where exactly fast radio bursts come from. They are extremely bright yet so brief, getting an accurate position is hard for many radio telescopes. Without knowing where precisely these bursts originate, we cannot study the galaxies they are found in. And without knowing the environments FRBs are formed in, we cannot fully solve their mysteries. </p>
<p>One telescope in Australia is now helping us figure it out. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/521203/original/file-20230417-1956-ensh6k.jpg?ixlib=rb-1.1.0&rect=0%2C232%2C5725%2C3181&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521203/original/file-20230417-1956-ensh6k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521203/original/file-20230417-1956-ensh6k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521203/original/file-20230417-1956-ensh6k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521203/original/file-20230417-1956-ensh6k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521203/original/file-20230417-1956-ensh6k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521203/original/file-20230417-1956-ensh6k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Some of the ASKAP dishes.</span>
<span class="attribution"><span class="source">CSIRO (Author provided)</span></span>
</figcaption>
</figure>
<h2>The tool for the job</h2>
<p><a href="https://www.csiro.au/askap">CSIRO’s ASKAP radio telescope</a> (Australian Square Kilometre Array Pathfinder), located in the Western Australian desert, is a remarkable instrument. Made up of an array of 36 dishes separated by up to six kilometres, ASKAP can detect FRBs and <a href="https://astronomy.curtin.edu.au/research/craft/">pinpoint them to their host galaxies</a>. </p>
<p>ASKAP can in fact perform its FRB search at the same time as observations for other science surveys. <a href="https://wallaby-survey.org/">One such ASKAP survey</a> will map the star-forming gas in galaxies across the Southern sky, helping us understand how galaxies evolve. </p>
<p>During a recent observation for this survey, ASKAP also detected a new FRB, and we were able to identify the galaxy it comes from – a nearby <a href="https://astronomy.swin.edu.au/cosmos/S/spiral+galaxy">spiral galaxy</a> much like our own Milky Way. </p>
<h2>A gas-filled galaxy</h2>
<p>ASKAP was able to find the cold neutral hydrogen gas – the source of star formation – in this spiral galaxy. As far as FRB host galaxies go, this is already a rare detection of this gas; only three other cases have been published so far. These <a href="https://iopscience.iop.org/article/10.3847/2041-8213/ac4ca8">had required follow-up observations</a>, or <a href="https://iopscience.iop.org/article/10.3847/2041-8213/ac2b35">relied on other older observations</a>, made with different telescopes.</p>
<p>Here, ASKAP gave us both the FRB and the gas surrounding it. It is the first simultaneous detection of these rarely overlapping occurrences.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/521001/original/file-20230414-20-jqg7qh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521001/original/file-20230414-20-jqg7qh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=495&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521001/original/file-20230414-20-jqg7qh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=495&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521001/original/file-20230414-20-jqg7qh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=495&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521001/original/file-20230414-20-jqg7qh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=622&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521001/original/file-20230414-20-jqg7qh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=622&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521001/original/file-20230414-20-jqg7qh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=622&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">ASKAP both found the cold hydrogen gas (white contours) in this spiral galaxy, and pinpointed an FRB near the centre (location given by the red ellipse). Glowacki et al. 2023; ESO and ASKAP.</span>
</figcaption>
</figure>
<p>Disturbed gas which ASKAP can detect can give us an indication that a galaxy merger recently happened, which tells us about the star forming history of the galaxy. In turn this gives us clues as to what may cause FRBs. </p>
<p>The previous studies of the gas surrounding FRBs found fast radio bursts reside in very dynamic systems, suggesting tumultuous galaxy mergers triggered the bursts.</p>
<p>For this particular FRB, however, the host galaxy environment is surprisingly calmer. Further studies will be needed to find out if overall we see disturbed gas environments for FRBs, or if there are distinct scenarios – and potentially multiple creation paths – for FRBs.</p>
<h2>More to come</h2>
<p>Given the uniqueness of such dual detections, this result showcases the strength and versatility of ASKAP. This is the first simultaneous detection of both an FRB and the gas in its host galaxy. </p>
<p>And this is just the start. ASKAP is set to detect and localise <a href="https://www.atnf.csiro.au/research/interferometry/public/How_CRACO_works.pdf">over a hundred FRBs a year</a>. By continuing to work collaboratively with each other, different survey groups will be able to untangle the mysteries behind FRBs, how they form, and their host galaxy environments. </p>
<hr>
<p><em>CSIRO acknowledges the Wajarri Yamaji as the Traditional Owners and native title holders of the Inyarrimanha Ilgari Bundara, our Murchison Radio-astronomy Observatory site, where ASKAP is located.</em></p><img src="https://counter.theconversation.com/content/203557/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marcin Glowacki does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>One of the few examples of a fast radio burst and the slow-moving, star forming gas in its origin galaxy has been linked together – thanks to observations from a CSIRO telescope.Marcin Glowacki, Research Associate, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2016222023-03-16T12:36:48Z2023-03-16T12:36:48ZWater in space – a ‘Goldilocks’ star reveals previously hidden step in how water gets to planets like Earth<figure><img src="https://images.theconversation.com/files/515568/original/file-20230315-1821-gn9l6v.jpg?ixlib=rb-1.1.0&rect=28%2C45%2C1249%2C1038&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The star system V883 Orionis contains a rare star surrounded by a disk of gas, ice and dust.</span> <span class="attribution"><a class="source" href="http://www.eso.org/public/images/eso1626a/">A. Angelich (NRAO/AUI/NSF)/ALMA (ESO/NAOJ/NRAO)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Without water, life on Earth could not exist as it does today. Understanding the history of water in the universe is critical to understanding how planets like Earth come to be.</p>
<p>Astronomers typically refer to the journey water takes from its formation as individual molecules in space to its resting place on the surfaces of planets as “the water trail.” The trail starts in the interstellar medium with hydrogen and oxygen gas and ends with oceans and ice caps on planets, with icy moons orbiting gas giants and icy comets and asteroids that orbit stars. The beginnings and ends of this trail are easy to see, but the middle has remained a mystery.</p>
<p><a href="https://www.cv.nrao.edu/%7Ejtobin/">I am an astronomer</a> who studies the formation of stars and planets using observations from radio and infrared telescopes. In a new paper, my colleagues and I describe the <a href="https://www.nature.com/articles/s41586-022-05676-z">first measurements ever made</a> of this previously hidden middle part of the water trail and what these findings mean for the water found on planets like Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="The progression of a star system from a cloud of dust and gas into a mature star with orbiting planets." src="https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Star and planet formation is an intertwined process that starts with a cloud of molecules in space.</span>
<span class="attribution"><a class="source" href="https://www.nrao.edu/pr/2012/clumpcores/">Bill Saxton, NRAO/AUI/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>How planets are formed</h2>
<p>The formation of stars and planets is intertwined. The so-called “emptiness of space” – or the interstellar medium – in fact contains <a href="https://doi.org/10.1146/annurev.aa.32.090194.001203">large amounts of gaseous hydrogen</a>, smaller amounts of other gasses and <a href="https://doi.org/10.1086/162480">grains of dust</a>. Due to gravity, some pockets of the interstellar medium will become <a href="https://doi.org/10.1086/311687">more dense as particles attract each other</a> and form clouds. As the density of these clouds increases, atoms begin to collide more frequently and <a href="https://doi.org/10.1086/381775">form larger molecules</a>, including water that forms <a href="https://doi.org/10.1080/0144235X.2015.1046679">on dust grains and coats the dust in ice</a>.</p>
<p>Stars begin to form when parts of the collapsing cloud reach a certain density and heat up enough to start fusing hydrogen atoms together. Since only a small fraction of the gas initially collapses into the newborn protostar, the rest of the gas and dust <a href="https://doi.org/10.48550/arXiv.1001.1404">forms a flattened disk of material</a> circling around the spinning, newborn star. Astronomers call this a proto-planetary disk.</p>
<p>As icy dust particles collide with each other inside a proto-planetary disk, <a href="https://doi.org/10.1051/0004-6361/200811158">they begin to clump together</a>. The process continues and eventually forms the familiar objects of space like asteroids, comets, rocky planets like Earth and gas giants like Jupiter or Saturn.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A cloudy filament against a backdrop of stars." src="https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=679&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=679&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=679&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=854&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=854&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=854&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Gas and dust can condense into clouds, like the Taurus Molecular Cloud, where collisions between hydrogen and oxygen can form water.</span>
<span class="attribution"><a class="source" href="http://www.eso.org/public/images/eso1209a/">ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey 2</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Two theories for the source of water</h2>
<p>There are two potential pathways that water in our solar system could have taken. The first, called <a href="https://doi.org/10.1051/0004-6361/200810846">chemical inheritance</a>, is when the water molecules originally formed in the interstellar medium are delivered to proto-planetary disks and all the bodies they create without going through any changes. </p>
<p>The second theory is called <a href="https://doi.org/10.1051/0004-6361/201628509">chemical reset</a>. In this process, the heat from the formation of the proto-planetary disk and newborn star breaks apart water molecules, which then reform once the proto-planetary disk cools.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Models of protium and deuterium." src="https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Normal hydrogen, or protium, does not contain a neutron in its nucleus, while deuterium contains one neutron, making it heavier.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Hydrogen_Deuterium_Tritium_Nuclei_Schmatic-en.svg">Dirk Hünniger/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>To test these theories, astronomers like me look at the ratio between normal water and a special kind of water called semi-heavy water. Water is normally made of two hydrogen atoms and one oxygen atom. Semi-heavy water is made of one oxygen atom, one hydrogen atom and one atom of deuterium – a heavier isotope of hydrogen with an extra neutron in its nucleus. </p>
<p>The ratio of semi-heavy to normal water is a guiding light on the water trail – measuring the ratio can tell astronomers a lot about the source of water. <a href="https://doi.org/10.1051/0004-6361/202039084">Chemical models</a> and <a href="https://doi.org/10.1086/591506">experiments</a> have shown that about 1,000 times more semi-heavy water will be produced in the cold interstellar medium <a href="https://doi.org/10.1126/science.1258055">than in the conditions of a protoplanetary disk</a>. </p>
<p>This difference means that by measuring the ratio of semi-heavy to normal water in a place, astronomers can tell whether that water went through the chemical inheritance or chemical reset pathway.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A star surrounded by a ring of gas and dust." src="https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">V883 Orionis is a young star system with a rare star at its center that makes measuring water in the proto-planetary cloud, shown in the cutaway, possible.</span>
<span class="attribution"><a class="source" href="https://public.nrao.edu/news/water-v883-orionis/">ALMA (ESO/NAOJ/NRAO), B. Saxton (NRAO/AUI/NSF)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Measuring water during the formation of a planet</h2>
<p>Comets have a ratio of semi-heavy to normal water almost perfectly in line with <a href="https://doi.org/10.2458/azu_uapress_9780816531240-ch037">chemical inheritance</a>, meaning the water hasn’t undergone a major chemical change since it was first created in space. Earth’s ratio sits somewhere in between the inheritance and reset ratio, making it unclear where the water came from.</p>
<p>To truly determine where the water on planets comes from, astronomers needed to find a goldilocks proto-planetary disk – one that is just the right temperature and size to allow observations of water. Doing so has <a href="https://doi.org/10.1051/0004-6361/201935994">proved to be incredibly difficult</a>. It is possible to detect semi-heavy and normal water when water is a gas; unfortunately for astronomers, the vast majority of proto-plantary disks are very cold and <a href="https://doi.org/10.1126/science.1239560">contain mostly ice</a>, and it is nearly <a href="https://doi.org/10.1051/0004-6361:20031277">impossible to measure water ratios</a> from ice at interstellar distances. </p>
<p>A breakthrough came in 2016, when my colleagues and I were studying proto-planetary disks around a rare type of young star called FU Orionis stars. Most young stars consume matter from the proto-planetary disks around them. FU Orionis stars are unique because they consume matter about 100 times faster than typical young stars and, as a result, <a href="https://doi.org/10.1146/annurev-astro-081915-023347">emit hundreds of times more energy</a>. Due to this higher energy output, the proto-planetary disks around FU Orionis stars are heated to much higher temperatures, turning ice into water vapor out to large distances from the star.</p>
<p>Using the <a href="https://public.nrao.edu/telescopes/alma/">Atacama Large Millimeter/submillimeter Array</a>, a powerful radio telescope in northern Chile, <a href="https://ui.adsabs.harvard.edu/abs/2016Natur.535..258C/abstract">we discovered</a> a large, warm proto-planetary disk around the Sunlike young star V883 Ori, about 1,300 light years from Earth in the constellation Orion.</p>
<p>V883 Ori emits 200 times more energy than the Sun, and my colleagues and I recognized that it was an ideal candidate to observe the semi-heavy to normal water ratio. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A radio image of the disk around V883 Ori." src="https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=672&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=672&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=672&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=844&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=844&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=844&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The proto-planetary disk around V883 Ori contains gaseous water, shown in the orange layer, allowing astronomers to measure the ratio of semi-heavy to normal water.</span>
<span class="attribution"><a class="source" href="https://public.nrao.edu/news/water-v883-orionis/#PRimage2">ALMA (ESO/NAOJ/NRAO), J. Tobin, B. Saxton (NRAO/AUI/NSF)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Completing the water trail</h2>
<p>In 2021, the Atacama Large Millimeter/submillimeter Array took measurements of V883 Ori for six hours. The data revealed a <a href="https://doi.org/10.1038/s41586-022-05676-z">strong signature of semi-heavy and normal water</a> coming from V883 Ori’s proto-planetary disk. We measured the ratio of semi-heavy to normal water and found that the ratio was very <a href="https://doi.org/10.1051/0004-6361/202039084">similar to ratios found in comets</a> as well as the ratios found <a href="https://doi.org/10.1051/0004-6361/201322845">in younger protostar systems</a>.</p>
<p>These results fill in the gap of the water trail forging a direct link between water in the interstellar medium, protostars, proto-planetary disks and planets like Earth through the process of inheritance, not chemical reset.</p>
<p>The new results show definitively that a substantial portion of the water on Earth most likely formed billions of years ago, before the Sun had even ignited. Confirming this missing piece of water’s path through the universe offers clues to origins of water on Earth. Scientists have previously suggested that most water on Earth <a href="https://doi.org/10.1051/0004-6361/201935554">came from comets impacting the planet</a>. The fact that Earth has less semi-heavy water than comets and V883 Ori, but more than chemical reset theory would produce, means that water on Earth likely came from more than one source.</p><img src="https://counter.theconversation.com/content/201622/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Tobin receives funding from NASA, </span></em></p>Astronomers have long known where water is first formed in the universe and how it ends up on planets, asteroids and comets. A recent discovery has finally answered what happens in between.John Tobin, Scientist, National Radio Astronomy ObservatoryLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1984022023-02-13T13:25:27Z2023-02-13T13:25:27ZWhy does the Earth spin?<figure><img src="https://images.theconversation.com/files/506911/original/file-20230127-14841-6vhvy8.jpg?ixlib=rb-1.1.0&rect=7%2C30%2C5096%2C3356&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">There are many pieces of evidence to help explain why the Earth spins, and some major mysteries.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/students-looking-at-globe-in-classroom-royalty-free-image/142020176">Jose Luis Pelaez Inc/DigitalVision via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why does the Earth spin? Sara H., age 5, New Paltz, New York</strong></p>
</blockquote>
<hr>
<p>A globe was the first thing I ever bought with my own money. I was maybe 5 years old, and I was really excited to take it home. As I quickly discovered, you can spin it in the direction that the earth actually spins.</p>
<p>There’s an imaginary line between the North Pole and the South Pole. We call it the rotation axis. For the Earth, the rotation axis points toward a bright star, Polaris, which is visible on clear nights in the Northern Hemisphere.</p>
<figure class="align-right ">
<img alt="A series of images of Earth seen from a satellite shows the planet rotating through a single day." src="https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Satellite images over one day show Earth rotating on its axis.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:EpicEarth-Globespin-tilt-23.4.gif">NASA/EPIC, edit by Tdadamemd</a></span>
</figcaption>
</figure>
<p>If you want to know which way to spin your globe, make the goofy “thumbs-up” sign with your right hand. Imagine your thumb is the Earth’s rotation axis, pointing to the North Pole. Your fingers will naturally curl around your hand, and the direction those fingers are pointing is the way Earth spins.</p>
<p>Every 24 hours, the Earth makes a full rotation, spinning west to east, which is why the sun rises in the east and sets in the west and the stars at night appear to move across the sky.</p>
<p>To understand why this happens, let’s see what we can learn from other bodies in space.</p>
<h2>Everything spins</h2>
<p>The Sun also spins. In fact, it spins in the same direction the Earth does. </p>
<p>Not only that, the Earth orbits the Sun in the same direction, as do all the other planets and more than a million asteroids and dwarf planets.</p>
<p>Most are spinning in the same direction, too. Jupiter and Saturn spin quite a bit faster than Earth, taking only about 10 hours to rotate. Saturn’s spin is a little bit tilted, so we get to <a href="https://en.wikipedia.org/wiki/Saturn#/media/File:Saturnoppositions-animated.gif">see changing views of its rings</a> over time.</p>
<figure class="align-center ">
<img alt="Image of five moons of various sizes and part of Saturn's rings" src="https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=423&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=423&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=423&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=531&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=531&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=531&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Cassini spacecraft took this image showing part of Saturn’s rings, made of billions of small chunks of ice and rock, and five of its moons.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/jpl/group-portrait">NASA/JPL-Caltech/Space Science Institute</a></span>
</figcaption>
</figure>
<p>There are two funky exceptions: Uranus appears to have been tipped over on its side. Nobody knows exactly how. Maybe it collided with another planet. Venus is also odd – it spins backward. We don’t know for sure whether it formed that way or got knocked over. Most scientists now think its spin has been <a href="https://doi.org/10.1051/0004-6361/201628701">reversed over time</a> by <a href="https://doi.org/10.1038/275037a0">tidal forces</a> involving the Sun and Venus’ thick atmosphere.</p>
<p>All that leads <a href="https://www.uml.edu/sciences/physics/faculty/laycock-silas.aspx">astronomers like me</a> to wonder: Is there something about how the solar system formed that kind of “baked in” that direction of spin?</p>
<h2>Birth of a star</h2>
<p>For more clues, we can look at a young star, one that is just forming its system of planets.</p>
<p>A famous one is called <a href="https://www.cnn.com/2022/04/29/world/exocomet-discovery-beta-pictoris-scn/index.html">Beta Pictoris</a>. It is surrounded by a thin disk of dust, gas and little bits called planetesimals; they range in size from a grain of sand to rocks maybe up to the size of a mountain. Astronomers are pretty sure the disk formed from material left over when the star was born.</p>
<p>Every <a href="https://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve">star is born</a> from a cloud of gas and dust that moves through space surrounded by other similar clouds. The force of gravity causes these clouds to tug on one another as they pass, which makes them slowly rotate.</p>
<p>Even when one of these clouds <a href="https://spaceplace.nasa.gov/nebula/en/">collapses to form a star</a>, it continues to rotate. The star forms, spinning at the center of a flat pancake of rotating gas and dust called a <a href="https://public.nrao.edu/news/2018-alma-survey-disks/">protoplanetary disk</a>. All of it – the star, the gas, the dust – is spinning in the same direction.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Illustration of a star in the center of a slanted ring of debris shown as glowing against the star's light, with a planet in the foreground." src="https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An artist’s drawing shows what a planet orbiting Beta Pictoris might look like.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Artist%E2%80%99s_impression_of_the_planet_Beta_Pictoris_b.jpg">ESO L. Calçada/N. Risinger (skysurvey.org)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An image of the star from the Hubble Space Telescope show its main debris ring and what appears to be a second ring slightly off tilt." src="https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=440&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=440&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=440&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Hubble Space Telescope captured actual images of Beta Pictoris. Astronomers blocked out light from the star in the photo so the protoplanetary disk would be visible.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Beta_Pictoris#/media/File:HST_betaPictoris_comb.jpg">David Golimowski/Johns Hopkins University, NASA, ESA</a></span>
</figcaption>
</figure>
<p>Astronomers think that our solar system looked a lot like Beta Pictoris in its early years.</p>
<p>We think that inside the disk, the gas and dust can stick together in a <a href="https://astronomy.com/magazine/news/2022/06/the-physics-of-accretion">process called accretion</a>. As a baby planet starts to grow, it gets heavier, and its gravity attracts more and more little pieces.</p>
<p>When the baby planet gets massive enough, the force of gravity begins crushing it, <a href="https://exoplanets.nasa.gov/faq/43/how-do-planets-form/">making it denser</a>. Because of that, like an ice skater drawing in her arms to spin, the planet spins faster. Rising pressure in the core causes the core to melt. Denser materials sink toward the core, and lighter materials float to the planet’s surface. We end up with a planet with an iron core surrounded by rock, and maybe on the outer parts stuff like water and ice.</p>
<p>That’s <a href="https://education.nationalgeographic.org/resource/core">what we see in our solar system</a>.</p>
<h2>What if Earth didn’t spin?</h2>
<p>Earth’s spin is important for life. It causes day and night. It’s also <a href="https://moon.nasa.gov/resources/444/tides">important for ocean tides</a>. Without the daily ebb and flow of water, it’s <a href="https://www.scientificamerican.com/article/moon-life-tides/">possible life would never have emerged</a> from the sea onto land.</p>
<p>So, astronomers believe Earth spins because the entire solar system was already rotating when Earth formed – but there are still a lot of questions about how planets’ spins change over time, and how spin affects the evolution of life. With <a href="https://exoplanetarchive.ipac.caltech.edu">more than 5,000 planets now known beyond the solar system</a>, future scientists are going to be busy exploring.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>Editor’s note: This article was updated to remove the reference to Mercury.</em></p><img src="https://counter.theconversation.com/content/198402/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Silas Laycock receives funding from NSF and NASA. He is affiliated with UMass Lowell, and the American Astronomical Society. </span></em></p>An astronomer takes us on a tour of the universe to learn about the birth of stars and planets and how they get their spin.Silas Laycock, Professor of Astronomy, UMass LowellLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1901632022-09-08T17:13:12Z2022-09-08T17:13:12ZHow massive stars steal planets – new research<figure><img src="https://images.theconversation.com/files/483215/original/file-20220907-16-pplied.jpeg?ixlib=rb-1.1.0&rect=91%2C61%2C2464%2C1417&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">There could be a planetary heist going on in the star-forming region NGC 3324 in the Carina Nebula.</span> <span class="attribution"><span class="source">NASA/James Webb Telescope</span></span></figcaption></figure><p>Our Sun has a rather lonely existence in the Milky Way galaxy. It sits on its own, four light years away from the nearest star, with only its planetary system for company. But it wasn’t always like this. We almost exclusively observe young stars in groups, so-called stellar nurseries, where they brush shoulders with stellar siblings.</p>
<p>These stellar nurseries are densely populated places, where hundreds of thousands of stars often reside in the same volume of space that the Sun inhabits on its own. Violent interactions, in which stars exchange energy, occur frequently, but not for long. After a few million years, the groups of stars dissipate, populating the Milky Way with more stars.</p>
<p>Our new paper, <a href="https://academic.oup.com/mnrasl/article-abstract/516/1/L91/6691413?redirectedFrom=fulltext">published in the Monthly Notices of the Royal Astronomical Society</a>, shows how massive stars in such stellar nurseries can steal planets away from each other – and what the signs of such theft are.</p>
<p>Almost immediately after young stars are born, <a href="https://exoplanets.nasa.gov/faq/43/how-do-planets-form/">planetary systems begin to form</a> around them. We have had indirect evidence of this for more than 30 years. Observations of the light from young stars display an <a href="https://iopscience.iop.org/article/10.1086/320685">unexpected excess</a> of infrared radiation. This was (and still is) explained as originating from small dust particles (100th of a centimetre) orbiting the star in a disc of material. It is from these dust particles that planets are (eventually) formed.</p>
<p>The field of star and planet formation underwent a revolution in late 2014 when the first images of planet-forming discs around stars were seen with the <a href="https://www.almaobservatory.org/en/home/">Atacama Large Millimetre Array (Alma)</a> telescope in the Chilean desert. The first, and subsequent, images from Alma were nothing short of spectacular. Many of the discs <a href="https://almascience.eso.org/almadata/lp/DSHARP/">had features and structures</a> that can be attributed to the presence of fully formed, Jupiter-like planets.</p>
<figure class="align-center ">
<img alt="Images of planet-forming disks." src="https://images.theconversation.com/files/483211/original/file-20220907-17-1d1rn.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/483211/original/file-20220907-17-1d1rn.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=749&fit=crop&dpr=1 600w, https://images.theconversation.com/files/483211/original/file-20220907-17-1d1rn.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=749&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/483211/original/file-20220907-17-1d1rn.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=749&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/483211/original/file-20220907-17-1d1rn.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=941&fit=crop&dpr=1 754w, https://images.theconversation.com/files/483211/original/file-20220907-17-1d1rn.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=941&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/483211/original/file-20220907-17-1d1rn.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=941&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">ALMA’s high-resolution images of planet-forming discs.</span>
<span class="attribution"><span class="source">Credit: ALMA (ESO/NAOJ/NRAO), S. Andrews et al.; N. Lira</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Planet formation happens rapidly after the onset of star formation, and certainly while the star is still interacting with its siblings in the stellar nursery. Because planets form so quickly, they will be affected by the densely populated star-forming environment. Planets can have their orbits altered, which can manifest in several ways.</p>
<h2>Wandering planets</h2>
<p>Sometimes, the distance of the planet from the host star becomes either smaller or larger, but more often there is a change to the shape of the orbit - usually becoming less circular (more “eccentric”). Occasionally, a planet is liberated from its orbit around its host star and <a href="https://theconversation.com/rogue-planets-how-wandering-bodies-in-interstellar-space-ended-up-on-their-own-174622">becomes “free-floating”</a> in the star-forming region, meaning it is not bound to any star by gravity.</p>
<p>A significant fraction of free-forming planets are captured, becoming gravitationally bound to a different star than the one around which they formed. A similar number of planets are even stolen from their orbit - directly exchanged between stars without first being free-floating. </p>
<p>In studying this great planetary heist, we have learned that planets that formed in the most populous star-forming regions may be easily captured or stolen by stars that are very much heavier than our own Sun. Stars form with a wide range of masses. Our Sun is slightly unusual in that it is around twice as heavy as the average mass star in the universe. However, a relatively small number of stars are heavier still, and these <a href="https://www.bartol.udel.edu/%7Eowocki/preprints/Sapporo_review_Aug05.pdf">“OB-type” stars </a> dominate the light we see in the Milky Way (and other galaxies). </p>
<h2>Beasties</h2>
<p>These massive stars are very bright but have much shorter lives than the Sun, and in some instances, they live for only several million years (rather than billions). We might, therefore, not expect to find planets around them. </p>
<p>However, in 2021, the B-star Exoplanet Abundance Study (Beast), led by researchers at the University of Stockholm, <a href="https://www.nature.com/articles/s41586-021-04124-8">discovered a planet</a> orbiting over 550 times the Earth-Sun distance from a star weighing up to ten times the mass of the Sun, and another planet orbiting at 290 times the Earth-Sun distance around a star nine times the mass of the Sun. </p>
<p>The Beast collaboration found these planets (“Beasties”) orbiting stars in the <a href="http://www.pas.rochester.edu/%7Eemamajek/scocen.pdf">Sco
Cen star-forming region</a>, which is currently gradually dissolving into the Milky Way. The original explanation put forward for these Beasties is that they formed just like the gas giant planets in our Solar System, but they are more massive and further out because they are a scaled-up version of our own planetary system.</p>
<p>Massive stars, however, emit copious quantities of ultraviolet radiation, which can evaporate away the gas from which giant planets such as Jupiter and Saturn require to form. So how do Beasties end up around them?</p>
<p>We know from our <a href="https://academic.oup.com/mnras/article/514/1/920/6590831">previous work</a> that planet theft and capture can happen in populous star-forming regions, and so we looked in our simulations for planets that were captured or stolen by massive stars.</p>
<p>Our new explanation for the Beasties is that they ended up in their orbits due to a planetary heist - they were born around other stars and were subsequently captured or stolen by the massive stars. These planetary systems are usually on wide (at least 100 Earth-Sun) orbits, and are highly eccentric - very different to the circular, close-in planets in our Solar System, which we think formed there. </p>
<p>Perhaps there is a captured planet in our Solar System - <a href="https://academic.oup.com/mnrasl/article/460/1/L109/2589689">the elusive and hypothetical Planet 9</a> - but Jupiter and the other giant planets formed around our Sun. </p>
<p>Our computer simulations also appear to predict the frequency of these systems (one or two per star-forming region), and the orbital characteristics of the Beasties.
Future observations will shed more light on the origin of these planets, but for now they represent yet another exciting discovery in the field of exoplanet science.</p><img src="https://counter.theconversation.com/content/190163/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Richard Parker receives funding from the Royal Society</span></em></p>We may have a stolen planet in our own Solar System.Richard Parker, Lecturer in Astrophysics, University of SheffieldLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1719982021-11-25T16:33:54Z2021-11-25T16:33:54ZWhy it’s location, location, location, even when it comes to galaxy evolution<figure><img src="https://images.theconversation.com/files/433612/original/file-20211124-21-1ynavrc.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4000%2C4000&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A composite image of the data collected by the ALMA telescope in Chile, showing spiral galaxies in the Virgo Cluster.</span> <span class="attribution"><span class="source">ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO)/T. Brown (VERTICO)</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Star formation — the conversion of gas into stars — is arguably the most important process in the universe. Yet there are regions of space that are so tempestuous, so inhospitable that star formation can be completely halted in the galaxies that reside there. </p>
<p>Astronomers have spent the last 50 years asking: Why is star formation linked to the region of space in which a galaxy lives? And how is it stopped?</p>
<p>A new research project, <a href="https://doi.org/10.3847/1538-4365/ac28f5">the Virgo Environment Traced in Carbon Monoxide (VERTICO) Survey</a>, tries to answer these questions using the world’s most advanced ground-based telescope. The goal is to reveal the influence of so-called galaxy environments on molecular gas, <a href="http://loke.as.arizona.edu/%7Eckulesa/research/overview.html">the raw fuel for star formation</a>, in detail.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/W45H783Q0bU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The VERTICO survey examines star formation in the Virgo Cluster.</span></figcaption>
</figure>
<h2>A hostile neighbourhood</h2>
<p>VERTICO is focused on a particularly extreme region of space called <a href="http://www.atlasoftheuniverse.com/galgrps/vir.html">the Virgo Cluster</a>, named for its location in the Virgo constellation in the night sky. This cluster contains thousands of galaxies bound together by gravity into one vast superstructure. Galaxy clusters such as this one are the ideal place to observe the effects of environment on star formation.</p>
<p>To understand just how extreme the Virgo Cluster is, it is helpful to place it in the context of our own galactic neighbourhood. The Milky Way resides in a rather <a href="https://doi.org/10.1086/316548">benign group of approximately 80 galaxies</a> that is spread out over five million light-years. In contrast, the Virgo Cluster is more than 1,000 times the mass of the Milky Way, and contains thousands of galaxies in a region of space that is only about three times the size of the Milky Way’s group. </p>
<p>Such a large amount of mass in such a small volume causes extraordinary gravitational forces, which in turn accelerate galaxies to speeds of millions of kilometres per hour and superheat the plasma that permeates the cluster to millions of degrees Celsius. It is these violent conditions that give rise to a class of physical phenomena so powerful they can stop hundreds or even thousands of galaxies from forming stars.</p>
<p><a href="https://nrc.canada.ca/en/stories/whats-killing-galaxies-large-survey-reveals-how-star-formation-shut-down-extreme-regions-universe">VERTICO is a Canadian-led collaboration</a> of international astronomers that used <a href="https://www.almaobservatory.org/en/home/">the Atacama Large Millimeter Array (ALMA) in the Chilean Andes</a> to provide some of the most detailed images ever taken of the star-forming gas in Virgo Cluster galaxies. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/433613/original/file-20211124-17-1p19qb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a comma-shaped image of an orange spiral galaxy" src="https://images.theconversation.com/files/433613/original/file-20211124-17-1p19qb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/433613/original/file-20211124-17-1p19qb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=540&fit=crop&dpr=1 600w, https://images.theconversation.com/files/433613/original/file-20211124-17-1p19qb3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=540&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/433613/original/file-20211124-17-1p19qb3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=540&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/433613/original/file-20211124-17-1p19qb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=679&fit=crop&dpr=1 754w, https://images.theconversation.com/files/433613/original/file-20211124-17-1p19qb3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=679&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/433613/original/file-20211124-17-1p19qb3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=679&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Galaxies NGC 4567 and NGC 4568 shown in composite radio data from ALMA with molecular gas in red/orange and optical data from the Hubble Space Telescope with stars in white/blue.</span>
<span class="attribution"><span class="source">(ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO)/T. Brown (VERTICO))</span></span>
</figcaption>
</figure>
<p>With these state-of-the-art data, we are able to identify the physical processes that are affecting how galaxies form their stars by observing their influence on 51 galaxies within the Virgo Cluster.</p>
<p>When we studied the beautiful images captured, we found that, in the Virgo Cluster, external physical processes are capable of reaching far into galaxies to perturb their molecular gas, affecting how stars are born and the galaxy evolves.</p>
<p>Over the next few years, our team will continue to mine this rich resource for insights into how stars form and galaxies grow in extreme environments such as the Virgo Cluster.</p>
<h2>How do galaxies grow?</h2>
<p>A valid question to ask of any scientist is, why does this matter? </p>
<p>From an academic perspective, one of the most satisfying things about astronomy is that simple questions can lead us straight to the frontiers of human understanding. Basic questions such as “Why do stars form?” and “How do galaxies grow?” sit right at the heart of the VERTICO collaboration’s research and will provide the foundation on which the next generation of astronomy will be built.</p>
<p>Astronomy research is a great Canadian, global and human success story. The VERTICO collaboration consists of almost 40 researchers from nine countries, each with their own culture and language. This team has come together to conduct cutting-edge work using the world’s most advanced telescope that has been <a href="https://www.almaobservatory.org/en/about-alma/global-collaboration/">built in Chile using North American, European, Asian and South American technology and expertise</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/433614/original/file-20211124-26-aq186x.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a striking image of an orange spiral galaxy on a dark background" src="https://images.theconversation.com/files/433614/original/file-20211124-26-aq186x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/433614/original/file-20211124-26-aq186x.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/433614/original/file-20211124-26-aq186x.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/433614/original/file-20211124-26-aq186x.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/433614/original/file-20211124-26-aq186x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/433614/original/file-20211124-26-aq186x.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/433614/original/file-20211124-26-aq186x.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Spiral galaxy NGC 4254 is among the thousands of galaxies living and dying by the extreme physical processes in the Virgo Cluster. The galaxy is seen here in radio from ALMA with molecular gas in red/orange and optical from Hubble Space Telescope with stars in white/blue.</span>
<span class="attribution"><span class="source">(ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO)/T. Brown (VERTICO))</span></span>
</figcaption>
</figure>
<p>Scientific projects such as VERTICO drive an exchange of people, ideas and funding between organizations and across borders that is of critical importance to the social, economic and academic fabric of our society.</p><img src="https://counter.theconversation.com/content/171998/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Toby Brown works for the National Research Council Canada, the primary national research and technology organization of the Government of Canada.</span></em></p>Studying the extreme environment of the Virgo Cluster — which comprises thousands of galaxies — helps us learn what factors can affect and start or stop star formation.Toby Brown, Postdoctoral fellow, Astrophysics, McMaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1635752021-06-29T12:07:28Z2021-06-29T12:07:28Z‘Laws of nature turned up to 11’: astronomers spot two neutron stars being swallowed by black holes<figure><img src="https://images.theconversation.com/files/408783/original/file-20210629-19-11qb29b.jpg?ixlib=rb-1.1.0&rect=1%2C9%2C1304%2C912&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Carl Knox/OzGrav/Swinburne Univ.</span></span></figcaption></figure><p>One of the best things about being an astronomer is being able to discover something new about the universe. In fact, maybe the only thing better is discovering it twice. And that’s exactly what my colleagues and I have done, by making two separate observations, just ten days apart, of an entirely new type of astronomical phenomenon: a neutron star circling a black hole before being gobbled up.</p>
<p>The two observations were made in January 2020, by the <a href="https://www.ligo.caltech.edu/page/what-is-ligo">Laser Interferometer Gravitational-wave Observatory (LIGO)</a> and the <a href="https://www.virgo-gw.eu/">Virgo Observatory</a>, both of which detect gravitational waves from the distant cosmos. </p>
<p>After 18 months of painstaking analysis, our discoveries are <a href="https://doi.org/10.3847/2041-8213/ac082e">published today in The Astrophysics Journal Letters</a>. The new observations open up new avenues to study the life cycle of stars, the nature of space-time, and the behaviour of matter at extreme pressures and densities.</p>
<p>The first observation of a neutron star-black hole system was made on January 5 2020. LIGO and Virgo observed gravitational waves — distortions in the very fabric of space-time — produced by the final 30 seconds of the dying orbit of the neutron star and black hole, followed by their inevitable collision. The discovery is named GW200105. </p>
<p>Remarkably, just ten days later, LIGO and Virgo detected gravitational waves from a second collision between a neutron star and a black hole. This event is named GW200115. Both collisions happened around 900 million years ago, long before the first dinosaurs appeared on Earth.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/dACjwnMhUJg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Artist’s impression of a neutron star orbiting and colliding with a black hole – Carl Knox/OzGrav/Swinburne Univ.</span></figcaption>
</figure>
<p>Neutron stars and black holes are among the most extreme objects in the universe. They are the fossil relics of massive dead stars. When a star that is more than eight times as massive as the Sun runs out of fuel, it undergoes a spectacular explosion called a supernova. What remains can be a neutron star or a black hole. </p>
<p>Neutron stars are typically between 1.5 and 2 times as massive as the Sun, but are so dense that all their mass is packed into an object the size of a city. At this density, atoms can no longer sustain their structure, and dissolve into a stream of free quarks and gluons: the building blocks of protons and neutrons.</p>
<p>Black holes are even more extreme. There is no upper limit to how massive a black hole can be, but all black holes have two things in common: a point of no return at their surface called an “event horizon”, from which not even light can escape; and a point at their centre called a “singularity”, at which the laws of physics as we understand them break down. </p>
<p>It is fair to say black holes are an enigma. One of the holy grails of 21st-century physics and astronomy is to find a deeper understanding of the laws of nature by observing these strange and extreme objects.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">Gravitational waves discovered: the universe has spoken</a>
</strong>
</em>
</p>
<hr>
<h2>A new type of star system</h2>
<p>Neutron stars orbiting black hole companions have long been thought to exist. LIGO and Virgo had been searching for them for more than a decade, but they have remained elusive until now.</p>
<p>So why are we so confident we’ve now seen not one such system, but two? </p>
<p>When LIGO and Virgo observe gravitational waves, the first question on our minds is “what caused them?” To find that out, we use two things: our observational data, and supercomputer simulations of different types of astronomical events that could plausibly explain those data. </p>
<p>By comparing the simulations to our real observations, we look for those characteristics that best match our data, homing in on the likely ones and ruling out the unlikely ones.</p>
<p>For the first discovery (GW200105), we determined that the most likely source of the gravitational waves was the final few orbits, and eventual collision, between an object around 8.9 times the mass of the Sun, with an object around 1.9 times the mass of the Sun. Given the masses involved, the most plausible explanation is that the heavier object is a black hole, and the lighter one is a neutron star. </p>
<p>Similarly, from the second (GW200115), we determined that its most likely source was the final few orbits and collision of a 5.7-solar-mass black hole with a 1.5-solar-mass neutron star.</p>
<p>There is no definitive smoking gun that the lighter objects are neutron stars, and in principle they could be very light black holes, although we consider this explanation unlikely. By far the best hypothesis is that our new observations are consistent with the merger of neutron stars and black holes.</p>
<h2>Stellar fossil-hunting</h2>
<p>Our discoveries have several intriguing implications. Neutron star-black hole systems allow us to piece together the evolutionary history of stars. Gravitational-wave astronomers are like stellar fossil-hunters, using the relics of exploded stars to understand how massive stars form, live and die. </p>
<p>We have been doing this for several years with LIGO/Virgo’s observations of <a href="https://theconversation.com/when-black-holes-meet-inside-the-cataclysms-that-cause-gravitational-waves-54236">pairs of black holes</a> and <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">pairs of neutron stars</a>. The newly discovered rarer pairs, containing one of each, are fascinating pieces of the stellar fossil record. </p>
<p>For the first time we have directly measured the rate at which neutron stars merge with black holes: we think there are likely to be tens or hundreds of thousands such collisions across the universe per year. With more observations, we will measure the rate more precisely.</p>
<p>What happens to the neutron stars after they’ve been gobbled up? Now we’re really looking at the laws of nature turned up to 11. When neutron stars merge with black holes, they are deformed, imprinting information about their exotic form of matter onto the gravitational waves we observe on Earth. </p>
<p>This can reveal the composition of neutron stars, which in turn tells us about how quarks and gluons behave at extreme pressure and density. It doesn’t tell us what’s going on behind the black hole’s event horizon, although another aspect of our discoveries is that we can look for hints of new physics in black holes in the gravitational-wave signals.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/when-black-holes-meet-inside-the-cataclysms-that-cause-gravitational-waves-54236">When black holes meet: inside the cataclysms that cause gravitational waves</a>
</strong>
</em>
</p>
<hr>
<p>When LIGO and Virgo resume observing in mid-2022 after an upgrade to boost their sensitivity still further, we will see more collisions between neutron stars and black holes. In the coming decade we expect to amass thousands more gravitational-wave detections. </p>
<p>Over time we hope to piece together the laws of nature that will help us understand the inner workings of the most extreme and impenetrable objects in the universe.</p><img src="https://counter.theconversation.com/content/163575/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rory Smith does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Gravitational waves reveal the demise of super-dense neutron stars spiralling into their black hole companions - the first time such strange and exotic star systems have ever been observed.Rory Smith, Lecturer in Astrophysics, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1338772020-04-24T12:22:19Z2020-04-24T12:22:19ZHow the Hubble Space Telescope opened our eyes to the first galaxies of the universe<figure><img src="https://images.theconversation.com/files/322098/original/file-20200321-22614-1c9vb6z.jpg?ixlib=rb-1.1.0&rect=0%2C57%2C373%2C246&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The launch of Hubble Space Telescope on April 24, 1990. This photo captures the first time that there were shuttles on both pad 39a and 39b.
</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>The <a href="http://nasa.gov/hubble">Hubble Space Telescope</a> launched on the 24th of April, 30 years ago. It’s an impressive milestone especially as its expected lifespan was just 10 years.</p>
<p>One of the primary reasons for the Hubble telescope’s longevity is that it can be serviced and improved with new observational instruments through Space Shuttle visits. </p>
<p>When Hubble, or HST, first launched, its instruments could observe ultraviolet light with wavelengths shorter than the eye can see, as well as optical light with wavelengths visible to humans. A maintenance mission in 1997 added an instrument to observe near infrared light, which are longer wavelengths than people can see. Hubble’s new infrared eyes provided two new major capabilities: the ability to see farther into space than before and see deeper into the dusty regions of star formation. </p>
<p><a href="https://www.as.arizona.edu/people/faculty/rodger-i-thompson">I am an astrophysicist at the University of Arizona</a> who has used near infrared observations to better understand how the universe works, from star formation to cosmology. Some 35 years ago, I was given the chance to build a near infrared camera and spectrometer for Hubble. It was the chance of a lifetime. The camera my team designed and developed has changed the way humans see and understand the universe. The instrument was built at Ball Aerospace in Boulder, Colorado, under our direction.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/330225/original/file-20200423-47820-1279cti.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/330225/original/file-20200423-47820-1279cti.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/330225/original/file-20200423-47820-1279cti.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=296&fit=crop&dpr=1 600w, https://images.theconversation.com/files/330225/original/file-20200423-47820-1279cti.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=296&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/330225/original/file-20200423-47820-1279cti.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=296&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/330225/original/file-20200423-47820-1279cti.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=372&fit=crop&dpr=1 754w, https://images.theconversation.com/files/330225/original/file-20200423-47820-1279cti.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=372&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/330225/original/file-20200423-47820-1279cti.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=372&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The light we can see with our eyes is part of a range of radiation known as the electromagnetic spectrum. Shorter wavelengths of light are higher energy, and longer wavelengths of light are lower energy. The Hubble Space Telescope sees primarily visible light (indicated here by the rainbow), as well as some infrared and ultraviolet radiation.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/content/explore-light">NASA/JHUAPL/SwRI</a></span>
</figcaption>
</figure>
<h2>Seeing further and earlier</h2>
<p><a href="https://www.biography.com/scientist/edwin-hubble">Edwin Hubble</a>, HST’s namesake, discovered in the early 1900s that the universe is expanding and that the light from distant galaxies was shifted to longer, redder wavelengths, a phenomenon called the redshift. The greater the distance, the larger the shift. This is because the further away an object is, the longer it takes for the light to reach us here on Earth and the more the universe has expanded in that time.</p>
<p>The Hubble ultraviolet and optical instruments had taken images of the most distant galaxies ever seen, known as the Northern Hubble Deep Field, or NHDF, which were released in 1996. These images, however, had reached their distance limit due to the redshift, which had shifted all of the light of the most distant galaxies out of the visible and into the infrared. </p>
<p>One of the new instruments added to Hubble in the second maintenance mission has the awkward name, the <a href="https://spacetelescope.org/about/general/instruments/nicmos/">Near Infrared Camera and Multi-Object Spectrometer</a>, NICMOS, pronounced “Nick Moss.” The near infrared cameras on NICMOS observed regions of the NHDF and discovered even more distant galaxies with all of their light in the near infrared.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/330244/original/file-20200423-47788-dhzzix.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/330244/original/file-20200423-47788-dhzzix.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=606&fit=crop&dpr=1 600w, https://images.theconversation.com/files/330244/original/file-20200423-47788-dhzzix.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=606&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/330244/original/file-20200423-47788-dhzzix.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=606&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/330244/original/file-20200423-47788-dhzzix.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=762&fit=crop&dpr=1 754w, https://images.theconversation.com/files/330244/original/file-20200423-47788-dhzzix.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=762&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/330244/original/file-20200423-47788-dhzzix.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=762&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A typical image taken with NICMOS. It shows a gigantic star cluster in the center of our Milky Way. NICMOS, thanks to its infrared capabilities, is able to look through the heavy clouds of dust and gas in these central regions.</span>
<span class="attribution"><a class="source" href="https://spacetelescope.org/about/general/instruments/nicmos/">NASA/JHUAPL/SwRI</a></span>
</figcaption>
</figure>
<p>Astronomers have the privilege of watching things happen in the past which they call the “lookback time.” Our best measurement of the age of the universe is 13.7 billion years. The distance that light travels in one year is called a light year. The most distant galaxies observed by NICMOS were at a distance of almost 13 billion light years. This meant that the light that NICMOS detected had been traveling for 13 billion years and showed what the galaxies looked like 13 billion years ago, a time when the universe was only about 5% of its current age. These were some of the first galaxies ever created and were forming new stars at rates that were more than a thousand times the rate at which most galaxies form stars in the current universe.</p>
<h2>Hidden by dust</h2>
<p>Although astronomers have studied star formation for decades, many questions remain. Part of the problem is that most stars are formed in clouds of molecules and dust. The dust absorbs the ultraviolet and most of the optical light emitted by forming stars, making it difficult for Hubble’s ultraviolet and optical instruments to study the process. </p>
<p>The longer, or redder, the wavelength of the light, the less is absorbed. That is why sunsets, where the light must pass through long lengths of dusty air, appear red. </p>
<p>The near infrared, however, has an even easier time passing through dust than the red optical light. NICMOS can look into star formation regions with the superior image quality of Hubble to determine the details of where the star formation occurs. A good example is the iconic Hubble image of <a href="https://www.nasa.gov/image-feature/eagle-nebula-s-pillars-of-creation-in-infrared">the Eagle Nebula</a>, also known as the pillars of creation. </p>
<p>The optical image shows majestic pillars which appear to show star formation over a large volume of space. The NICMOS image, however, shows a different picture. In the NICMOS image, most of the pillars are transparent with no star formation. Stars are only being formed at the tip of the pillars. The optical pillars are just empty dust reflecting the light of a group of nearby stars.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/330226/original/file-20200423-47826-1bi0uc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/330226/original/file-20200423-47826-1bi0uc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/330226/original/file-20200423-47826-1bi0uc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=626&fit=crop&dpr=1 600w, https://images.theconversation.com/files/330226/original/file-20200423-47826-1bi0uc4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=626&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/330226/original/file-20200423-47826-1bi0uc4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=626&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/330226/original/file-20200423-47826-1bi0uc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=787&fit=crop&dpr=1 754w, https://images.theconversation.com/files/330226/original/file-20200423-47826-1bi0uc4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=787&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/330226/original/file-20200423-47826-1bi0uc4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=787&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Eagle Nebula in visible light.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/goddard/2017/messier-16-the-eagle-nebula">NASA, ESA and the Hubble Heritage Team (STScI/AURA)</a></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/330222/original/file-20200423-47788-ux54hw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/330222/original/file-20200423-47788-ux54hw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/330222/original/file-20200423-47788-ux54hw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=563&fit=crop&dpr=1 600w, https://images.theconversation.com/files/330222/original/file-20200423-47788-ux54hw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=563&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/330222/original/file-20200423-47788-ux54hw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=563&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/330222/original/file-20200423-47788-ux54hw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=707&fit=crop&dpr=1 754w, https://images.theconversation.com/files/330222/original/file-20200423-47788-ux54hw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=707&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/330222/original/file-20200423-47788-ux54hw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=707&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">In this Hubble Space Telescope image is the Eagle Nebula’s Pillars of Creation. Here, the pillars are seen in infrared light, which pierces through obscuring dust and gas and unveils a more unfamiliar — but just as amazing — view of the pillars.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/eagle-nebula-s-pillars-of-creation-in-infrared">NASA, ESA/Hubble and the Hubble Heritage Team</a></span>
</figcaption>
</figure>
<h2>The dawning of the age of infrared</h2>
<p>When NICMOS was added into the HST in 1997 NASA had no plans for a future infrared space mission. That rapidly changed as the results from NICMOS became apparent. Based on the data from NICMOS, scientists learned that fully <a href="https://www.nationalgeographic.com/news/2014/1/140107-hubble-oldest-frontier-science-space-astronomy/">formed galaxies existed in the universe much earlier than expected</a>. The NICMOS images also confirmed that the <a href="https://www.nasa.gov/feature/goddard/2019/mystery-of-the-universe-s-expansion-rate-widens-with-new-hubble-data">expansion of the universe is accelerating</a> rather than slowing down as previously thought. The NHDF infrared images were followed by the Hubble Ultra Deep Field images in 2005, which further showed the power of near infrared imaging of distant young galaxies. So NASA decided to invest in the <a href="http://www.jwst.nasa.gov">James Webb Space Telescope</a>, or JWST, a telescope much larger than HST and completely dedicated to infrared observations. </p>
<p>On Hubble, a near infrared imager was added to the third version of the Wide Field camera which was installed in May of 2009. This camera used an improved version of the NICMOS detector arrays that had more sensitivity and a wider field of view. The James Webb Space Telescope has much larger versions of the NICMOS detector arrays that have more wavelength coverage than the previous versions.</p>
<p>The James Webb Space Telescope, scheduled to be launched in March 2021, followed by the Wide Field Infrared Survey Telescope, form the bulk of future space missions for NASA. These programs were all spawned by the near infrared observations by HST. They were enabled by the original investment for a near infrared camera and spectrometer to give Hubble its infrared eyes. With the James Webb Space Telescope, astronomers expect to see the very first galaxies that formed in the universe.</p>
<p>[<em>Deep knowledge, daily.</em> <a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=deepknowledge">Sign up for The Conversation’s newsletter</a>.]</p><img src="https://counter.theconversation.com/content/133877/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rodger I. Thompson was the Principal Investigator for the Near Infrared Camera and Multi-Object Spectrometer, NICMOS. He was responsible for the execution of a contract to Arizona Board of Regents from NASA to deliver NICMOS as a Hubble Space Telescope Instrument and carry out a scientific investigation with it. Prof. Thompson received summer salary from this contract at his University pay rate during the execution of the contract which ended in 2004. Prof. Thompson is not currently receiving any external funding.</span></em></p>Thirty years ago the Hubble Space Telescope began snapping photos of distant stars, providing a time machine that has taken astronomers back to when the universe was less than a billion years old.Rodger I. Thompson, Professor of Astronomy, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1210752020-01-21T13:49:57Z2020-01-21T13:49:57ZEven planets have their (size) limits<figure><img src="https://images.theconversation.com/files/297273/original/file-20191016-98661-1c4okmk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A planet-forming disk made from rock and gas surrounds a young star. </span> <span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/news/news.php?feature=927">NASA/JPL-Caltech/SwRI/MSSS/ Gerald Eichstädt /Seán Doran</a></span></figcaption></figure><p>Scientists have discovered over 4,000 exoplanets outside of our Solar System, according to <a href="https://exoplanetarchive.ipac.caltech.edu/">NASA’s Exoplanet Archive</a>.</p>
<p>Some of these planets orbit <a href="https://en.wikipedia.org/wiki/Circumbinary_planet">multiple stars</a> at the same time. Certain planets are so close to their star that it takes only a handful of days to make one revolution, compared to the Earth which takes 365.25 days. Others slingshot around their star with <a href="http://www.hzgallery.org/913_2.png">extremely oblong orbits</a>, unlike the Earth’s circular one. When it comes to how exoplanets behave and where they exist, there are many possibilities.</p>
<p>And yet, when it comes to sizes of planets, specifically their mass and radius, there are some limitations. And for that, we have physics to blame.</p>
<p><a href="https://scholar.google.com/citations?user=u6_GYWkAAAAJ&hl=en&oi=ao">I am a planetary astrophysicist</a> and I try to understand what makes a <a href="https://www.youtube.com/watch?v=AKA0z6SOHws">planet able to support life</a>. I look at the chemical <a href="http://www.nataliehinkel.com">connection between stars and their exoplanets</a> and how the interior structure and mineralogy of different sized planets compare to each other. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This sketch illustrates a family tree of exoplanets starting from the protoplanetary disk, which is a swirling disk of gas and dust surrounding a planet (much like a stellar disk but smaller). Gas and dust is pulled onto the planet, depending on the planet’s mass and gravity.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/ames/new-branch-in-exoplanet-family-tree">NASA/Ames Research Center/JPL-Caltech/Tim Pyle</a></span>
</figcaption>
</figure>
<h2>Rocky versus gaseous planets</h2>
<p>In our Solar System, we have two kinds of planets: small, <a href="https://en.wikipedia.org/wiki/Terrestrial_planet">rocky</a>, dense planets that are similar to Earth and large, <a href="https://en.wikipedia.org/wiki/Gas_giant">gaseous planets</a> like Jupiter. From what we astrophysicists have detected so far, most planets fall into these two categories. </p>
<p>In fact, when we look at the data from planet-hunting missions such as the <a href="https://www.nasa.gov/mission_pages/kepler/overview/index.html">Kepler mission</a> or from the <a href="https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite">Transiting Exoplanet System Satellite</a>, there is a gap in the planet sizes. Namely, there <a href="https://arxiv.org/abs/1703.10375">aren’t many planets that fulfill the definition of a “super-Earth,”</a> with a radius of one and a half to twice Earth’s radius and a mass that is five to 10 times greater.</p>
<p>So the question is, why aren’t there any super-Earths? Why do astronomers only see small rocky planets and enormous gaseous planets?</p>
<p>The differences between the two kinds of planets, and the reason for this super-Earth gap, has everything to do with a planet’s atmosphere – especially when the planet is forming. </p>
<p><a href="https://en.wikipedia.org/wiki/Star_formation">When a star is born</a>, a huge ball of gas comes together, starts to spin, collapses in on itself and ignites a <a href="https://en.wikipedia.org/wiki/Fusion">fusion reaction</a> within the star’s core. This process isn’t perfect; there is a lot of extra gas and dust left over after the star is formed. The extra material continues to rotate around the star until it eventually forms into a stellar disk: a flat, ring-shaped collection of gas, dust, and rocks. </p>
<p>During all of this motion and commotion, the dust grains slam into each other, forming pebbles which then grow into larger and larger boulders until they form planets. As the planet grows in size, its mass and therefore gravity increases, allowing it to capture not only the accumulated dust and rocks – but also the gas, which forms an atmosphere. </p>
<p>There is lots of gas within the stellar disk – after all, hydrogen and helium are the most common elements in stars and in the universe. However, there is considerably less rocky material because only a limited amount was made during star formation.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Comparison of confirmed super-Earth planets compared to the size of the Earth.</span>
<span class="attribution"><a class="source" href="https://exoplanets.nasa.gov/news/207/finding-another-earth/">NASA/Ames/JPL-Caltech</a></span>
</figcaption>
</figure>
<h2>The trouble with super-Earths</h2>
<p>If a planet remains relatively small, with a radius less than 1.5 times Earth’s radius, then its gravity is not strong enough to hold onto a huge amount of atmosphere, like what’s on Neptune or Jupiter. If, however, it continues to grow larger, then it captures more and more gas which forms an atmosphere that causes it to swell to the size of Neptune (four times Earth’s radius) or Jupiter, 11 times Earth’s radius. </p>
<p>Therefore, a planet either stays small and rocky, or it becomes a large, gaseous planet. The middle ground, where a super-Earth might be formed, is very difficult because, once it has enough mass and gravitational pull, it needs the exact right circumstances to stop the avalanche of gas from piling onto the planet and puffing it up. This is sometimes referred to as “unstable equilibrium” – such that when a body (or a planet) is slightly displaced (a little bit more gas is added) it departs further from the original position (and becomes a giant planet).</p>
<p>Another factor to consider is that once a planet is formed, it doesn’t always stay in the same orbit. Sometimes planets move or migrate towards their host star. As the planet gets closer to the star, its atmosphere heats up causing the atoms and molecules to move very fast and escape the planet’s gravitational pull. So some of the small rocky planets are actually the cores of <a href="https://arxiv.org/pdf/1706.02050.pdf">bigger planets that have been stripped of their atmosphere</a>. </p>
<p>So, while there are no super huge rocky planets or small fluffy planets, there is still a huge amount of diversity in planet sizes, geometries and compositions. </p>
<p>[ <em>You’re smart and curious about the world. So are The Conversation’s authors and editors.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklysmart">You can get our highlights each weekend</a>. ]</p><img src="https://counter.theconversation.com/content/121075/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Natalie Hinkel receives funding from the NASA Nexus for Exoplanet System Science research coordination network based out of Arizona State University. This funding is used to research exoplanet habitability.</span></em></p>Why isn’t there an endless variety of planets in the universe? An astrophysicist explains why planets only come in two flavors.Natalie Hinkel, Planetary Astrophysicist, Senior Research Scientist at the Southwest Research Institute and Co-Investigator for the Nexus for Exoplanet System Science (NExSS), Arizona State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/965062018-05-18T09:18:19Z2018-05-18T09:18:19ZWhen did the lights first come on in the universe? A galaxy close to the dawn of time gives a clue<figure><img src="https://images.theconversation.com/files/219421/original/file-20180517-26300-88ah5v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Galaxy cluster MACS J1149.5+2223 taken with the Hubble Space Telescope. The inset image is the very distant galaxy MACS1149-JD1</span> <span class="attribution"><span class="source">ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, W. Zheng (JHU), M. Postman (STScI), the CLASH Team, Hashimoto et al.</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>It is springtime in the Northern hemisphere. Countless buds that have been waiting patiently on the stems and branches of trees and shrubs are now blossoming into life. The cosmic equivalent of this season is the time between a few hundred million and a billion years after the Big Bang. This is when the first stars and galaxies ignited, spewing light into the dark universe. </p>
<p>It is a time in the history of the universe that we are desperate to chart, because it represents part of the cosmological story that we have yet to understand. Now astronomers have detected oxygen in a galaxy further away than ever before – and it existed just 500m years after the Big Bang. The results, <a href="http://nature.com/articles/doi:10.1038/s41586-018-0117-z">published in Nature</a>, are hugely important as they provide new insights into when the first stars formed. </p>
<p>The period of this “cosmic dawn” is important not only because this is when the first galaxies were born, but a crucial cosmic transition also took place. In this process, atoms in the electrically neutral intergalactic medium – a wide sea of hydrogen gas surrounding galaxies – were bombarded with ultraviolet radiation escaping from the first galaxies. This stripped away electrons from atoms and made the gas charged, or “ionised”.</p>
<p>The event, called the <a href="https://theconversation.com/after-our-universes-cosmic-dawn-what-happened-to-all-its-original-hydrogen-65527">Epoch of Reionisation</a>, is still mysterious. We’d like to know – or better yet, <em>see</em> – when this process started. Part of that quest involves finding the most distant galaxies.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/219236/original/file-20180516-155619-14remy0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/219236/original/file-20180516-155619-14remy0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=250&fit=crop&dpr=1 600w, https://images.theconversation.com/files/219236/original/file-20180516-155619-14remy0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=250&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/219236/original/file-20180516-155619-14remy0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=250&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/219236/original/file-20180516-155619-14remy0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=314&fit=crop&dpr=1 754w, https://images.theconversation.com/files/219236/original/file-20180516-155619-14remy0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=314&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/219236/original/file-20180516-155619-14remy0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=314&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of the Epoch of Reionisation.</span>
<span class="attribution"><span class="source">ESA C. Carreau</span></span>
</figcaption>
</figure>
<p>When we look out into the universe we detect light that has taken some appreciable time to traverse the gulf that separates us from other stars and galaxies. The light from the screen you are reading this on has taken about a third of a nanosecond to reach your eyes. Light from the nearest star beyond our sun takes four years to reach us. Amazingly, light from the galaxy at the centre of the new study, called MACS1149-JD1, has taken 13 <em>billion</em> years to be detected here on Earth. That means we see MACS1149-JD1 as it was 13 billion years in the past, around 500m years after the Big Bang.</p>
<h2>Powerful gaze</h2>
<p>Using a telescope called the <a href="http://www.almaobservatory.org/en/home/">Atacama Large Millimetre/sub-millimetre Array (ALMA)</a>, the scientists detected a strong signal (an emission line) within the distant galaxy. Just as a prism disperses the light of the sun into a rainbow spectrum, we can disperse the light of distant galaxies, too. This is called spectroscopy. Emission lines are bright spikes in the spectra of galaxies that originate from different elements that can each release light of a very specific energy. </p>
<p>This particular emission line came from ionised oxygen gas. Its presence tells us that the galaxy was forming stars at the time, because the energy required to ionise it must have come from massive, hot, young stars.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/219177/original/file-20180516-155623-19v0gc7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/219177/original/file-20180516-155623-19v0gc7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=221&fit=crop&dpr=1 600w, https://images.theconversation.com/files/219177/original/file-20180516-155623-19v0gc7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=221&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/219177/original/file-20180516-155623-19v0gc7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=221&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/219177/original/file-20180516-155623-19v0gc7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=278&fit=crop&dpr=1 754w, https://images.theconversation.com/files/219177/original/file-20180516-155623-19v0gc7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=278&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/219177/original/file-20180516-155623-19v0gc7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=278&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The ALMA Observatory.</span>
<span class="attribution"><span class="source">Carlos Padilla – AUI/NRAO</span></span>
</figcaption>
</figure>
<p>If we measured the same type of gas here on Earth, we would detect it at a wavelength of 0.088 millimetres. But other galaxies are receding away from us due to cosmic expansion, and this causes the light they emit to increase in wavelength during the time it takes for the photons to reach us. The more distant a galaxy is, the larger the increase in wavelength. </p>
<p>This is called <a href="http://astronomy.swin.edu.au/cosmos/C/cosmological+redshift">redshift</a>, and it ultimately tells us the ratio between the size of the universe when the light was first emitted and the size of the universe today. The oxygen emission line observed in MACS1149-JD1 is actually detected at 0.88 millimetres – its wavelength has been stretched by a factor of 10. This means that at the time the light was emitted, the universe was a factor of 10 times smaller than it is today, and just four per cent of its present age. </p>
<p>In this way, the ability to detect emission lines in distant galaxies allows us to pinpoint at what stage in cosmic history we are seeing them. But of course, the most distant galaxies are also the faintest – you need ever more powerful telescopes if you want to peer back further. </p>
<p>ALMA (consisting of 66 individual telescopes working together) is an incredibly powerful telescope – it is revolutionising our view of the early universe. Not only is it providing exquisite sensitivity, but operates in part of the electromagnetic spectrum that gives access to a wide range of emission lines.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/219367/original/file-20180517-155607-369ubf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/219367/original/file-20180517-155607-369ubf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/219367/original/file-20180517-155607-369ubf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/219367/original/file-20180517-155607-369ubf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/219367/original/file-20180517-155607-369ubf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/219367/original/file-20180517-155607-369ubf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/219367/original/file-20180517-155607-369ubf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Gravitational lensing.</span>
<span class="attribution"><span class="source">NASA, ESA & L. Calcada</span></span>
</figcaption>
</figure>
<p>To help matters, the team also exploited a natural telescope: a <a href="https://theconversation.com/method-to-weigh-galaxy-clusters-could-help-us-understand-mysterious-dark-matter-structures-85023">massive cluster of galaxies</a>. Light from MACS1149-JD1 has had to pass through this intervening cluster on its journey to ALMA. This is so massive that it significantly warps spacetime, meaning that the light is “bent” in a process called <a href="https://theconversation.com/how-we-managed-what-einstein-thought-was-impossible-and-used-his-theory-to-weigh-a-star-79050">gravitational lensing</a>. Gravitational lensing amplifies the brightness of MACS1149-JD1, making it a little easier to see.</p>
<h2>Indirect glimpse of first stars</h2>
<p>MACS1149-JD1 is not the <a href="https://en.wikipedia.org/wiki/GN-z11">most distant galaxy on record</a>, but what this new study adds to our understanding is an insight into the history of the formation of the galaxy. This happened hundreds of millions of years before the current observation, and much further back than even the most distant galaxy known. </p>
<p>In fact, the presence of oxygen in the galaxy tells us that star formation must have been going on for some time in MACS1149-JD1. That’s because oxygen can only be formed within stars in a process called stellar nucleosynthesis. But what we don’t know is when those stars first ignited.</p>
<p>By combining data from the <a href="https://www.nasa.gov/mission_pages/hubble/story/index.html">Hubble Space Telescope</a>, the <a href="http://www.eso.org/public/unitedkingdom/teles-instr/paranal-observatory/vlt/">European Southern Observatory’s Very Large Telescope</a> and the <a href="http://www.spitzer.caltech.edu/">Spitzer Space Telescope</a>, the authors made a model of the “stellar population” within MACS1149-JD1. This allowed them to estimate the mixture of stars that give rise to the emission from the galaxy observed in certain bands of the <a href="https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html">electromagnetic spectrum</a>.</p>
<p>The model involves estimating the “star formation history” of the galaxy, describing the rate of production of stars in the past. The modelling suggests that, in order to produce the observed emission, stars must have started forming just 250m years after the Big Bang, when the universe was just two per cent of its present age. In other words, MACS1149-JD1 was already a fairly well established galaxy, even at this early time. </p>
<p>This is a huge scientific accomplishment as it is currently impossible to observe galaxies that existed 250m years after the Big Bang. However, the new <a href="https://www.jwst.nasa.gov/">James Webb Space Telescope</a>, which is due for launch in 2020, may be able to do so. </p>
<p>But until then, thanks to the new study, we now have a way of indirectly studying when stars first formed in ancient galaxies like MACS1149-JD1. In effect, by observing the blossom, astronomers have estimated when the bud first opened.</p><img src="https://counter.theconversation.com/content/96506/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Geach receives funding from The Royal Society.</span></em></p>Astronomers have indirectly spotted some of the first stars in the universe by making their most distant detection of oxygen in a galaxy that existed just 500m years after the Big Bang.James Geach, Royal Society University Research Fellow, University of HertfordshireLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/964102018-05-11T04:49:34Z2018-05-11T04:49:34ZA giant ‘singing’ cloud in space will help us to understand how star systems form<figure><img src="https://images.theconversation.com/files/218381/original/file-20180510-184630-8kvekt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The dark band is the Dark Doodad Nebula, a place where new stars and planets can form.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/cafuego/25910801567/">Flickr/cafuego</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>We know that the birthplaces of stars are large molecular clouds of gas and dust found in space. </p>
<p>But what exactly determines the number and kind of stars and planets that are formed in these clouds? How was our Solar system nursed and how did it emerge from such a cloud billions of year ago?</p>
<p>These are mysteries that have been puzzling astronomers for decades, but research <a href="http://science.sciencemag.org/content/360/6389/635">published today in Science</a> adds an extra dimension to our understanding.</p>
<h2>A 3D approach</h2>
<p>Knowledge of the 3-dimensional structure of these clouds would be an important leap in our understanding of how stars and planets are born.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/from-pancakes-to-soccer-balls-new-study-shows-how-galaxies-change-shape-as-they-age-95379">From pancakes to soccer balls, new study shows how galaxies change shape as they age</a>
</strong>
</em>
</p>
<hr>
<p>The physics responsible for the formation of stars is also responsible for shaping the clouds. But even with the most advanced telescopes in the world we can only see the two-dimensional projections of clouds on the plane of the sky.</p>
<p>Thankfully, there is a way around this problem. A recently discovered type of structure in molecular clouds, called striations, was found to form because of waves.</p>
<p>Here enters Musca, a molecular cloud that “sings”. Musca is an isolated cloud in the Southern sky, below the Southern Cross, that looks like a thin needle (see top image). It is hundreds of light years away and stretches about 27 light years across, with a depth of about 20 light years and width up to a fraction of a light year.</p>
<p>Musca is surrounded by ordered hair-like striations produced by trapped waves of gas and dust caused by the global vibrations of the cloud.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/218373/original/file-20180510-34009-t7500v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/218373/original/file-20180510-34009-t7500v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/218373/original/file-20180510-34009-t7500v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=340&fit=crop&dpr=1 600w, https://images.theconversation.com/files/218373/original/file-20180510-34009-t7500v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=340&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/218373/original/file-20180510-34009-t7500v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=340&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/218373/original/file-20180510-34009-t7500v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=427&fit=crop&dpr=1 754w, https://images.theconversation.com/files/218373/original/file-20180510-34009-t7500v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=427&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/218373/original/file-20180510-34009-t7500v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=427&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">3D model of Musca molecular cloud.</span>
<span class="attribution"><span class="source">Aris Tritsis, ANU</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Trapped waves act like a fingerprint – they are unique and can be used to identify the sizes of the boundaries that trapped them. Boundaries are naturally created at the edges of clouds where their physical properties change abruptly.</p>
<p>Just like a cello and a violin make very distinct sounds, clouds with different sizes and structures will vibrate in very different manners – they will “sing” different “songs”.</p>
<h2>A ‘song’ in the cloud</h2>
<p>By using this concept and calculating the frequencies seen in observations of Musca it was possible to measure for the first time the third dimension of the cloud, the one that extends along our line of sight.</p>
<p>The frequencies found in the observations were scaled to the frequency range of human hearing to produce the “song of Musca”.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/K9cp2FWHGLc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A “singing” molecular cloud.</span></figcaption>
</figure>
<p>The results from this method were amazing. Despite the fact that Musca looks like a thin cylinder from Earth, the true size of its hidden dimension is not small at all. In fact, it is comparable to its largest visible dimension on the plane of the sky.</p>
<p><img src="https://cdn.theconversation.com/static_files/files/108/tritsis2.gif?1526006594" width="100%"></p>
<h4>No longer a thin cylinder when the extra dimension is revealed (Aris Tritsis)</h4>
<p>Musca is not actively forming stars. It will be millions of years before gravity can overcome all opposing forces that support the cloud.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/signals-from-a-spectacular-neutron-star-merger-that-made-gravitational-waves-are-slowly-fading-away-94294">Signals from a spectacular neutron star merger that made gravitational waves are slowly fading away</a>
</strong>
</em>
</p>
<hr>
<p>As a result, with its structure now determined, Musca can be used as a prototype laboratory against which we can compare our models and study the early stages of star formation.</p>
<p>We can use Musca to better constraint our numerical models and learn about our own Solar system. It could help solve many mysteries. For example, could the ices found in comets have formed in clouds rather than at a later time during the life of our solar system?</p><img src="https://counter.theconversation.com/content/96410/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Aris Tritsis does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A three-dimensional look and listen at a dark cloud in space sheds new light on the mystery of how our solar system formed billions of years ago.Aris Tritsis, Postdoctoral Fellow, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/953792018-04-23T20:08:43Z2018-04-23T20:08:43ZFrom pancakes to soccer balls, new study shows how galaxies change shape as they age<figure><img src="https://images.theconversation.com/files/215804/original/file-20180422-75093-1jvpzys.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Sombrero galaxy reveals the extremes of age and shape.
</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/multimedia/imagegallery/image_feature_283.html">NASA/ESA and The Hubble Heritage Team (STScI/AURA)</a></span></figcaption></figure><p>Galaxies are a fundamental part of the 13.7 billion-year-old universe. Understanding how a system as complex and striking as our own Milky Way galaxy formed after the Big Bang is one of the great themes of modern astronomy.</p>
<p>Our research, <a href="http://nature.com/articles/doi:10.1038/s41550-018-0436-x">published today in Nature Astronomy</a>, has identified a surprising connection between the age of a galaxy and its three-dimensional shape.</p>
<p>As galaxies get older they get rounder, and fall victim to the middle-aged spread that catches many of us humans here on Earth.</p>
<p>We’ve known for a long time that shape and age are linked in very extreme galaxies – that is, very flat ones and very round ones. But this is the first time we have shown this is true for all kinds of galaxies – all shapes, all ages, all masses. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/live-fast-die-young-a-massive-dead-red-galaxy-seen-for-the-first-time-in-the-early-universe-75774">Live fast, die young: a massive 'dead red' galaxy seen for the first time in the early Universe</a>
</strong>
</em>
</p>
<hr>
<h2>Unveiling the true face of a galaxy</h2>
<p>In this study we calculated both the age and shape of galaxies using different techniques.</p>
<p>Assigning an age to a galaxy is tricky. They don’t have a single birth date for when they suddenly popped into existence. </p>
<p>We assessed the average age of the stars in a galaxy as a measure of the galaxy’s age. Young galaxies have a large fraction of recently formed hot blue stars, whereas old galaxies mostly contain colder red stars formed shortly after the Big Bang.</p>
<p>Spectroscopy — splitting the light from a galaxy into many different colours — allows us to measure the <a href="https://newsroom.unsw.edu.au/news/science-tech/finding-our-sun%E2%80%99s-lost-siblings">average age of stars in a galaxy</a>. This technique gives a much higher precision than simply using blue or red images as is typically done.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185410/original/file-20170911-9414-nc2zxk.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/185410/original/file-20170911-9414-nc2zxk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/185410/original/file-20170911-9414-nc2zxk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=363&fit=crop&dpr=1 600w, https://images.theconversation.com/files/185410/original/file-20170911-9414-nc2zxk.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=363&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/185410/original/file-20170911-9414-nc2zxk.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=363&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/185410/original/file-20170911-9414-nc2zxk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=456&fit=crop&dpr=1 754w, https://images.theconversation.com/files/185410/original/file-20170911-9414-nc2zxk.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=456&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/185410/original/file-20170911-9414-nc2zxk.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=456&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A selection of SAMI galaxies imaged with the Hyper Suprime Cam on the Subaru Telescope in Hawaii.</span>
<span class="attribution"><span class="source">National Astronomical Observatory of Japan (NAOJ), Caroline Foster (The University of Sydney) and Dan Taranu (University of Western Australia)</span></span>
</figcaption>
</figure>
<p>To measure a galaxy’s <a href="https://theconversation.com/3d-view-helps-us-to-understand-how-galaxies-formed-and-evolved-81318">true three-dimensional shape</a> and ellipticity, you have to measure how its stars move around. </p>
<p>Ellipticity is simply a measure of how squashed a galaxy is with respect to a perfect sphere. An ellipticity of zero means a galaxy is a perfect sphere like a soccer ball. But as the measured ellipticity increases from zero towards one, the galaxy becomes more and more squashed – from a roundish pumpkin shape to a thin disk like a pancake.</p>
<p>We see galaxies as two-dimensional images projected onto the sky, but that doesn’t tell us what they really look like in three dimensions. If we can also measure how the stars in a galaxy are moving we can infer their true, three-dimensional shape. </p>
<p>Spectroscopy lets us do this via the <a href="https://theconversation.com/explainer-the-doppler-effect-7475">Doppler effect</a>. We can measure shifts in the wavelength of light emitted by stars, which depend on whether those stars are moving towards us or away from us, and so measure their motions. </p>
<p>We did this using <a href="https://sami-survey.org/">SAMI</a>, the Sydney-Australian-Astronomical-Observatory Multi-object Integral-Field Spectrograph, on the 3.9-metre <a href="https://www.aao.gov.au/about-us/AAT">Anglo-Australian Telescope</a> at Siding Spring Observatory. The SAMI instrument provides 13 optical fibre units that can “dissect” galaxies using spectroscopy, providing unique 3D data. </p>
<p>Over the past couple of years, the SAMI Galaxy Survey team has gathered 3D measurements for more than a <a href="https://www.aao.gov.au/news-media/media-releases/scientists-unveil-new-3D-view-of-galaxies">thousand galaxies</a> of all kinds, and with a hundred-fold range in mass.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/j4yxBwmLxms?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This astronomical time-lapse video features the unique SAMI instrument at the 3.9m Anglo-Australian Telescope and the beauty of the dark sky over Siding Spring Observatory. Credit: Ángel R. López-Sánchez (Australian Astronomical Observatory / Macquarie University)</span></figcaption>
</figure>
<h2>Changing the shape of galaxies</h2>
<p>So what do we learn about the processes that shape galaxies from this result? </p>
<p>Galaxies tend to form their stars in a pancake-like disk with high ellipticity. But these stars don’t stay in that thin disk as the galaxy ages. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215812/original/file-20180422-75110-1ll3bmo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/215812/original/file-20180422-75110-1ll3bmo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215812/original/file-20180422-75110-1ll3bmo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=564&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215812/original/file-20180422-75110-1ll3bmo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=564&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215812/original/file-20180422-75110-1ll3bmo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=564&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215812/original/file-20180422-75110-1ll3bmo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=709&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215812/original/file-20180422-75110-1ll3bmo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=709&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215812/original/file-20180422-75110-1ll3bmo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=709&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An edge-on view of spiral galaxy NGC 3501, a young galaxy with an extremely thin disk.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html">ESA/Hubble & NASA</a></span>
</figcaption>
</figure>
<p>There are lots of different gentle events, known as <a href="http://astronomy.swin.edu.au/cosmos/S/Secular+Evolution">secular processes</a>, that cause the disk to puff up, becoming rounder and less squashed. A galaxy can be bombarded by other, smaller galaxies. Even if a galaxy is isolated, internal dynamical processes can cause the disk to thicken.</p>
<p>The net result is, as a galaxy ages, its initial thin disk of stars starts to thicken – the middle-aged spread – and the galaxy becomes older, rounder and less squashed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215880/original/file-20180423-75093-u9nvcf.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/215880/original/file-20180423-75093-u9nvcf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215880/original/file-20180423-75093-u9nvcf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215880/original/file-20180423-75093-u9nvcf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215880/original/file-20180423-75093-u9nvcf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215880/original/file-20180423-75093-u9nvcf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215880/original/file-20180423-75093-u9nvcf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215880/original/file-20180423-75093-u9nvcf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Elliptical galaxy NGC 4660 is a much older and puffier galaxy than spiral galaxy NGC 3501.</span>
<span class="attribution"><a class="source" href="https://www.spacetelescope.org/images/heic0815b/">SA, NASA and E. Peng (Peking University, Beijing)</a></span>
</figcaption>
</figure>
<p>In some cases a galaxy can experience more extreme events that radically change its shape. <a href="https://www.space.com/22395-elliptical-galaxies.html">Elliptical galaxies</a>, <a href="https://www.nasa.gov/feature/goddard/2017/messier-87">such as M87</a>, are the oldest and roundest galaxies in the universe. </p>
<p>Astronomers think these galaxies are formed in major mergers — dramatic collisions between galaxies that result in one massive galaxy being entirely consumed by another. </p>
<p>Because these events are so significant, they scatter all the stars out of the disk of a galaxy, resulting in a much rounder shape. They also prevent any new stars being formed after the merger, causing the galaxy to age rapidly. The end result is an old, very round galaxy.</p>
<figure>
<iframe src="https://player.vimeo.com/video/43238292" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">The inevitable fate of our Milky Way: the collision between our galaxy and Andromeda. Credit: NASA / ESA / STScI / Columbia University / F. Summers / G. Besla / R. van der Marel.</span></figcaption>
</figure>
<h2>Closer to home</h2>
<p>If we look at our own Milky Way galaxy, which is more than 10 billion years old, we can see examples of this story. </p>
<p>The youngest part of the Milky Way, where stars are still being formed, is the thin disk, which has a very squashed, pancake-like shape. The Milky Way also contains rounder and older components, a thick disk and a bulge, but their origin is still mostly unknown.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/when-galaxies-collide-size-matters-if-you-want-to-know-the-fate-of-our-milky-way-91826">When galaxies collide, size matters if you want to know the fate of our Milky Way</a>
</strong>
</em>
</p>
<hr>
<p>We know that eventually the Milky Way will merge with our galactic neighbour, the Andromeda galaxy. <a href="http://adsabs.harvard.edu/abs/2012ApJ...753....9V">Predictions are</a> that this will result in a very round, very old giant elliptical galaxy. </p>
<p>So, by studying the processes that shape other nearby galaxies, we can learn a lot about the past, and the fate of our own.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/215860/original/file-20180423-75114-19vaw15.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215860/original/file-20180423-75114-19vaw15.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215860/original/file-20180423-75114-19vaw15.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215860/original/file-20180423-75114-19vaw15.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215860/original/file-20180423-75114-19vaw15.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215860/original/file-20180423-75114-19vaw15.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215860/original/file-20180423-75114-19vaw15.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighbouring Andromeda galaxy.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html">NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger</a></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/95379/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jesse van de Sande works for the University of Sydney and receives funding from the Australian Research Council (FL140100278). The Sydney-AAO Multi-object Integral field spectrograph (SAMI) was developed jointly by the University of Sydney and the Australian Astronomical Observatory. The SAMI Galaxy Survey is funded by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020, and other participating institutions. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013.
</span></em></p><p class="fine-print"><em><span>Nicholas Scott works for the University of Sydney and is funded by a University of Sydney Postdoctoral Research Fellowship.</span></em></p>As galaxies get older they get rounder, and fall victim to the middle-aged spread that catches many of us humans here on Earth.Jesse van de Sande, Postdoctoral Research Associate in Astronomy, University of SydneyNicholas Scott, Postdoctoral Research Fellow in Astronomy, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/901472018-01-19T10:08:26Z2018-01-19T10:08:26ZStudy of distant galaxies challenges our understanding of how stars form<figure><img src="https://images.theconversation.com/files/202446/original/file-20180118-158519-186b12q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">ESO/UltraVISTA team. Acknowledgement: TERAPIX/CNRS/INSU/CASU</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The most massive galaxies in our neighbourhood formed their stars billions of years ago, early in the history of the universe. At the present day, they produce very few new stars. Astronomers have long believed that is because they contain very little gas – a key ingredient necessary to produce stars. But our new study, published in <a href="http://em.rdcu.be/wf/click?upn=KP7O1RED-2BlD0F9LDqGVeSAjZUdc-2FqgpuTsX153V7IiU-3D_nxaMCHA8HKRN7Obv30-2BkpQSlaoIvL88II6d-2FeFNo6wAVblVhHRPm9FZ88ZZc-2BU0NtNEO6fwpQzC5sY8GGY-2FgUfoxQOAKiAg9T5k7kjv1Q3W-2B3ZnK4ggQt5KVx0u7OaIRBU5e9EzQsG5Um3gqO50LS-2FgP-2BBVZ3jbVzz7H-2F1GdFcRA54qYNA6-2Bm2Zqxi-2FEA36ouf2hq-2BaRnrlu4xuDpjhDm-2BsT5yRU-2B-2FQeiIiw8LV6EGBCNUaWinJ3lSyNcwlSPOYNtmsihT4AyRzvRCGDQUcBOg-3D-3D">Nature Astronomy</a>, is now challenging this long held view.</p>
<p>Through probing the extreme environments of faraway massive galaxies, we can learn not only about their evolution and the history of the universe, but most importantly about the fundamental processes regulating <a href="https://theconversation.com/uk/search?utf8=%E2%9C%93&q=star+formation">the formation of stars</a>. Given that stars produce most of the different types of atoms in our bodies and the world around us, understanding how they were formed is essential if we are to know where we came from.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/202447/original/file-20180118-158531-3vuror.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/202447/original/file-20180118-158531-3vuror.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202447/original/file-20180118-158531-3vuror.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202447/original/file-20180118-158531-3vuror.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202447/original/file-20180118-158531-3vuror.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202447/original/file-20180118-158531-3vuror.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202447/original/file-20180118-158531-3vuror.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Disc galaxy Messier 101.</span>
<span class="attribution"><span class="source">NASA, ESA, CXC, SSC, and STScI</span></span>
</figcaption>
</figure>
<p>Galaxies exist in two main types: disc and elliptical. Disc galaxies, including the Milky Way, are flat and contain large reservoirs of gas that they use to continually form stars. Elliptical galaxies are massive, round and stopped forming stars long ago. Most theories assume that at some point elliptical galaxies <a href="https://arxiv.org/abs/astro-ph/0502199">lost their gas reservoirs</a>, which caused the rate of star formation to drop. </p>
<h2>Distant light</h2>
<p>Our team investigated whether there are other ways in which distant, elliptical galaxies could have lost their ability to form stars. Distance to galaxies are measured by how bright its stars are, in light years (defined as how long it takes the light to reach us in one year). As it takes so long for the light from these faraway galaxies <a href="http://hubblesite.org/reference_desk/faq/answer.php.id=45&cat=galaxies">to reach us</a>, we can work out that they appear to us as they were 10 billion years ago. </p>
<p>Ideally we would want to directly observe the gas in these galaxies, but this is extremely challenging and would require several hours of observations per galaxy – and we need to look at thousands of galaxies. Instead, we opted to study dust. Dust (cold rather than hot) only represents 1% of the interstellar matter in a galaxy, but it is found wherever cold gas is. A galaxy that contains a lot of dust therefore also contains a lot of gas.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/202449/original/file-20180118-158531-1i9tbmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/202449/original/file-20180118-158531-1i9tbmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=596&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202449/original/file-20180118-158531-1i9tbmh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=596&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202449/original/file-20180118-158531-1i9tbmh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=596&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202449/original/file-20180118-158531-1i9tbmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=749&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202449/original/file-20180118-158531-1i9tbmh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=749&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202449/original/file-20180118-158531-1i9tbmh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=749&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Elliptical galaxy called ESO 306-17 in the southern sky.</span>
<span class="attribution"><span class="source">NASA, ESA and Michael West (ESO)</span></span>
</figcaption>
</figure>
<p>We used data from the <a href="http://cosmos.astro.caltech.edu/">Cosmological Evolution Survey (COSMOS)</a>, which covers a large patch of the sky observed by most major telescopes, on Earth and in space. We used images from infrared to radio wavelengths of light, which allows us to measure both the rate of star formation and the cold dust mass in galaxies. </p>
<p>Since the galaxies we are interested in are so far away, it is impossible to detect each galaxy individually in the existing infrared or radio data. Instead, we combined the light from 1,000 galaxies and determined how much gas they contain on average and how quickly they are forming stars. </p>
<p>As a result, we made an exciting discovery. Despite having low star formation rates, the elliptical galaxies contain surprisingly large amounts of gas: 100 times more than was expected. This is surprising in two ways. It challenges our standard view of elliptical galaxies as “boring” gas-poor objects. But it also forces us to rethink the basic view of star formation processes – we have always assumed that the presence of cold gas must lead to star formation. Here, we find that elliptical galaxies form stars far less efficiently than disk galaxies at the same epoch.</p>
<p>So why is that? Nine years ago, I <a href="https://arxiv.org/abs/0905.4669">predicted</a> this possibility from numerical simulations I had run as a PhD student. I found that in disc galaxies, the gravitational pull of the stars helps the gas to collapse to form new stars. In contrast, the gas in elliptical galaxies feels a weaker pull from the stars and does not collapse so easily. It is fascinating that the global morphology of a galaxy can control what happens at the smallest scales. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/202444/original/file-20180118-158550-cw4eco.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/202444/original/file-20180118-158550-cw4eco.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=854&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202444/original/file-20180118-158550-cw4eco.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=854&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202444/original/file-20180118-158550-cw4eco.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=854&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202444/original/file-20180118-158550-cw4eco.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1073&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202444/original/file-20180118-158550-cw4eco.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1073&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202444/original/file-20180118-158550-cw4eco.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1073&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Star forming nebula, where gas collapses to form new stars.</span>
<span class="attribution"><span class="source">ESA/NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>The next steps of our research will use new simulations and hopefully direct observations of the cold gas itself with the <a href="http://www.almaobservatory.org/en/home/">Atacama Large Millimeter/submillimeter Array (ALMA)</a>, an observatory in Chile, to improve our understanding of the complex interplay between star formation and galaxy morphology. This will shed light on universal processes ultimately happening in every galaxy, including our very own Milky Way.</p><img src="https://counter.theconversation.com/content/90147/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marie Martig does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Massive, far distant galaxies contain 100 times more gas than we thought possible.Marie Martig, Senior Lecturer in Astrophysics, Liverpool John Moores UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/856912017-10-30T14:03:50Z2017-10-30T14:03:50ZAre red skies at night a shepherd’s delight? An astronomer’s view<figure><img src="https://images.theconversation.com/files/191386/original/file-20171023-1717-qa2865.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Be warned?</span> <span class="attribution"><span class="source">C. P. Ewing</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Humans have always used simple observations of nature to try to understand our complex environment and even the wider cosmos. One such example is: “Red sky at night, shepherd’s delight” and “Red sky at morning, shepherd’s warning”. These sayings – <a href="https://www.scientificamerican.com/article/is-there-scientific-valid/">which date back to the Bible</a> (Matthew 16:2b–3) – suggest that a particularly red sunset means clear weather is coming and a particularly red sunrise means it’s going to be bad weather or possibly a stormy day.</p>
<p>There is a rich heritage of interpreting dusk and dawn sky colours, with different cultural groups and peoples having different traditions and sayings. For example, “shepherd’s delight” is typically replaced with “<a href="https://www.esrl.noaa.gov/gmd/grad/about/redsky/">sailor’s delight</a>” in the US version of the rhyme. But is there any truth behind such forecasting?</p>
<p>In mid latitudes such as Europe and the US, <a href="https://www.metoffice.gov.uk/learning/learn-about-the-weather/how-weather-works/global-circulation-patterns">weather systems mostly move in from the west</a>. It is this particular feature that can help us understand how the colour of the sky is linked to future weather patterns – and whether shepherds should bother paying attention to red skies.</p>
<h2>Shades of red</h2>
<p>During sunset or sunrise, the light from the sun will travel through a signficant fraction of the atmosphere and ultimately the troposphere – a region that contains clouds. There, sunlight interacts with gas molecules that are much smaller than the wavelength of light, a process physicists call <a href="http://www.atoptics.co.uk/atoptics/blsky.htm">Rayleigh scattering</a>. In this interaction, light is dispersed more effectively if its colour is blue rather than red. The reason the sun looks red at sunset or sunrise is because most of its blue light has been scattered away during the extra long journey through the atmosphere.</p>
<p>You can test this at home. Shine a torch through water that has one or two drops of milk added. Milk scatters light in a similar way to the gas molecules in the atmosphere, leaving the torch light looking red.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/MtIdcgp95Zw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>But sunset or sunrise don’t necessarily mean a bright, red sky. If there’s a lot of water vapour in the air this can make the sunset look more pink and orange – <a href="http://www.spc.noaa.gov/publications/corfidi/sunset/">muting the bright red colours</a>. This is an effect caused by water droplets being comparable or larger in size to the wavelength of light, which means they scatter all colour of light similarly.</p>
<p>An intensively red colour sky <a href="http://www.spc.noaa.gov/publications/corfidi/sunset/">requires a particularly dry and clear troposphere</a> along the path of the sunlight – so the air consists mostly of molecules smaller than water droplets, dust or pollutants. Such clear atmospheric conditions <a href="https://www.sciencedirect.com/science/article/pii/0004698179901689">are usually linked</a> to the leading side of a high pressure weather front moving in from the west – a phenomenon that usually means the next day will be dry and sunny. So it seems there is indeed some truth to the saying about red skies at night.</p>
<p>If the high pressure system is moving away to the east these atmospheric conditions are encountered by the light of the rising sun reaching us instead. As a result, red sky in the morning indicates a change in weather is imminent. Any light reaching us during sunset from the west would have to pass through more humid air. In addition, the atmosphere on the <a href="https://www.sciencedirect.com/science/article/pii/0004698179901689">trailing side of a high pressure system is usually also higher in pollutants</a>, which also helps scatter blue light.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/190716/original/file-20171017-30394-1rqxsr8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/190716/original/file-20171017-30394-1rqxsr8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=570&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190716/original/file-20171017-30394-1rqxsr8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=570&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190716/original/file-20171017-30394-1rqxsr8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=570&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190716/original/file-20171017-30394-1rqxsr8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=716&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190716/original/file-20171017-30394-1rqxsr8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=716&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190716/original/file-20171017-30394-1rqxsr8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=716&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Strange skies over Nottingham, UK, as a result of fine dust within the weather system linked to the passing hurricane Ophelia.</span>
<span class="attribution"><span class="source">Nottingham Trent Observatory: D Brown</span></span>
</figcaption>
</figure>
<p>But the colours of the sunset or sunrise can be far more complex and a result of events much further away from the observer other than weather. The air can contain not only water, but more complex pollutants and small dust particles. If these are all similar in size, the sun and the sky can take on orange-red colours, as well as lilac or purple. These particles can be picked up from wild fires and dust-storms. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/190780/original/file-20171018-32361-re4vr5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/190780/original/file-20171018-32361-re4vr5.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=446&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190780/original/file-20171018-32361-re4vr5.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=446&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190780/original/file-20171018-32361-re4vr5.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=446&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190780/original/file-20171018-32361-re4vr5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=560&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190780/original/file-20171018-32361-re4vr5.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=560&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190780/original/file-20171018-32361-re4vr5.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=560&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Smoke is green in the image above. This image is produced using aerosol sensors on polar-orbiting satellites.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Only recently this resulted in a phenomenon in the UK dubbed the <a href="http://www.mirror.co.uk/news/uk-news/britains-eerie-hurricane-sun-red-11359527">hurricane sun</a>. A weather system linked to the hurricane Ophelia had transported <a href="http://www.bbc.co.uk/news/uk-england-41635906">dust from North-Africa and the Iberian wild fires</a> in its clouds over the UK. As a result the noon sun was turned into a deep orange, tinging the landscape with an eerie light. Another example was the <a href="http://news.bbc.co.uk/1/hi/world/europe/8634944.stm">2010 eruption of Eyjafjallajökull</a>, a volcano in Iceland, that generated fine ash as well as Sulphate aerosols in the high atmosphere. </p>
<h2>Interstellar sunsets</h2>
<p>Red skies are far more than nice opportunities for a photo. They offer moments to contemplate how basic observations can reveal insights into future weather and even volcanic eruptions many thousands of miles away. Perhaps more surprisingly, they also help us to understand what lies outside our own planet.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/190713/original/file-20171017-30406-ibcg2w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/190713/original/file-20171017-30406-ibcg2w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=310&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190713/original/file-20171017-30406-ibcg2w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=310&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190713/original/file-20171017-30406-ibcg2w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=310&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190713/original/file-20171017-30406-ibcg2w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=389&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190713/original/file-20171017-30406-ibcg2w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=389&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190713/original/file-20171017-30406-ibcg2w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=389&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Two images of a dense cloud in space absorbing the light of background stars. The left shows the visual range and the right includes infra red. Overall, stars become reddened similar to the sun during sunset or sunrise.</span>
<span class="attribution"><span class="source">ESO</span></span>
</figcaption>
</figure>
<p>Space known as the “interstellar medium” is filled with dust and gas. Sometimes that can be bunched up in clouds and cause the light of distant stars to be significantly dimmed and reddened. When we look at this, it’s like we see hundreds of suns at the same time being turned into a redder colour. Understanding these “interstellar sunsets” is allowing us to <a href="http://articles.adsabs.harvard.edu//full/1930PASP...42..214T/0000218.000.html">explore what lies between us and other stars</a>.</p>
<p>That’s because particles near stars or in star-forming clouds can be present in or among the dust, helping to cause the red starlight. Ultimately, by studying these interstellar sunsets, we could work out exactly <a href="https://www.eso.org/public/news/eso0102/">what these particles are</a>. That means we could understand what elements help form stars and planets with their own atmospheres and sunsets and sunrises. So red skies not only bring shepherds’ delight – they bring astronomers delight as well.</p><img src="https://counter.theconversation.com/content/85691/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daniel Brown does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The science of red skies can also help us understand how stars form.Daniel Brown, Lecturer in Astronomy, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/811222017-07-24T08:06:31Z2017-07-24T08:06:31ZBooze in space: how the universe is absolutely drowning in the hard stuff<figure><img src="https://images.theconversation.com/files/179195/original/file-20170721-18128-14pw7he.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mine's a Star-opramen. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/retro-astronaut-mug-beer-pop-art-486571996?src=GRArIRYoATk-qqeZn7VeGg-1-7">Studioloks</a></span></figcaption></figure><p>A cold beer on a hot day or a whisky nightcap beside a coal fire. A well earned glass can loosen your thinking until you feel able to pierce the mysteries of life, death, love and identity. In moments like these, alcohol and the cosmic can seem intimately entwined. </p>
<p>So perhaps it should come as no surprise that the universe is awash with alcohol. In the gas that occupies the space between the stars, the hard stuff is almost all-pervasive. What is it doing there? Is it time to send out some big rockets to start collecting it?</p>
<p>The chemical elements around us reflect the history of the universe and the stars within it. Shortly after the Big Bang, protons were formed throughout the expanding, cooling universe. Protons are the nuclei of hydrogen atoms and building blocks for the nuclei of all the other elements. </p>
<p>These have mostly been manufactured since the Big Bang through nuclear reactions in the hot dense cores of stars. Heavier elements such as lead or gold are only fabricated in rare massive stars or incredibly explosive events. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/179175/original/file-20170721-18110-oqdban.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179175/original/file-20170721-18110-oqdban.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/179175/original/file-20170721-18110-oqdban.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=835&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179175/original/file-20170721-18110-oqdban.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=835&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179175/original/file-20170721-18110-oqdban.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=835&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179175/original/file-20170721-18110-oqdban.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1050&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179175/original/file-20170721-18110-oqdban.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1050&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179175/original/file-20170721-18110-oqdban.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1050&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ethanol molecule.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/File:Ethanol-3D-balls.png#/media/File:Ethanol-3D-balls.png">Wikimedia</a></span>
</figcaption>
</figure>
<p>Lighter ones such as carbon and oxygen are synthesised in the life cycles of very many ordinary stars – including our own sun eventually. Like hydrogen, they are among the most common in the universe. In the vast spaces between the stars, <a href="https://ay201b.wordpress.com/2011/04/12/course-notes/">typically</a> 88% of atoms are hydrogen, 10% are helium and the remaining 2% are chiefly carbon and oxygen.</p>
<p>Which is great news for booze enthusiasts. Each molecule of ethanol, the alcohol that gives us so much pleasure, includes nine atoms: two carbon, one oxygen and six hydrogen. Hence the chemical symbol C₂H₆O. It’s as if the universe turned itself into a monumental distillery on purpose. </p>
<h2>Interstellar intoxication</h2>
<p>The spaces between stars are known as the interstellar medium. The famous Orion Nebula is perhaps the best known example. It is the closest region of star formation to Earth and visible to the naked eye – albeit still more than 1,300 light years away. </p>
<p>Yet while we tend to focus on the colourful parts of nebulae like Orion where stars are emerging, this is not where the alcohol is coming from. Emerging stars produce intense ultraviolet radiation, which destroys nearby molecules and makes it harder for new substances to form. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179190/original/file-20170721-18113-gcen2i.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179190/original/file-20170721-18113-gcen2i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179190/original/file-20170721-18113-gcen2i.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=587&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179190/original/file-20170721-18113-gcen2i.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=587&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179190/original/file-20170721-18113-gcen2i.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=587&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179190/original/file-20170721-18113-gcen2i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=737&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179190/original/file-20170721-18113-gcen2i.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=737&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179190/original/file-20170721-18113-gcen2i.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=737&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Orion Nebula.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Orion_Nebula#/media/File:Orion_Nebula_-_Hubble_2006_mosaic_18000.jpg">Wikimedia</a></span>
</figcaption>
</figure>
<p>Instead you need to look to the parts of the interstellar medium that appear to astronomers as dark and cloudy, and only dimly illuminated by distant stars. The gas in these spaces is <a href="http://casswww.ucsd.edu/archive/public/tutorial/ISM.html">extremely cold</a>, slightly less than -260°C, or about 10°C above absolute zero. This makes it very sluggish. </p>
<p>It is also fantastically widely dispersed. At sea level on Earth, by my calculations there are roughly 3x10<sup>25</sup> molecules per cubic metre of air – that’s a three followed by 25 zeros, an enormously huge number. At passenger jet altitude, circa 36,000ft, the density of molecules is about a third of this value – say 1x10<sup>25</sup>. We would struggle to breathe outside the aircraft, but that’s still quite a lot of gas in absolute terms. </p>
<p>Now compare this to the dark parts of the interstellar medium, where there are typically 100,000,000,000 particles per cubic metre, or 1x10<sup>11</sup>, and often much less than even that. These atoms seldom come close enough to interact. Yet when they do, they can form molecules less prone to being blown apart by further high-speed collisions than when the same thing happens on Earth. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179196/original/file-20170721-18165-1tl87lr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179196/original/file-20170721-18165-1tl87lr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179196/original/file-20170721-18165-1tl87lr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179196/original/file-20170721-18165-1tl87lr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179196/original/file-20170721-18165-1tl87lr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179196/original/file-20170721-18165-1tl87lr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179196/original/file-20170721-18165-1tl87lr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179196/original/file-20170721-18165-1tl87lr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The proof is out there.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/very-bright-white-star-named-procyon-412689028?src=sMN_naWxfUHYuErfk0iKOQ-2-44">Tragoolchitr Jittasaiyapan</a></span>
</figcaption>
</figure>
<p>If an atom of carbon meets an atom of hydrogen, for instance, they can stick together as a molecule called <a href="https://link.springer.com/referenceworkentry/10.1007%2F978-3-642-11274-4_1807">methylidyne</a> (chemical symbol CH). Methylidyne is highly reactive and so is quickly destroyed on Earth, but it is common in the interstellar medium. </p>
<p>Simple molecules like these are more free to encounter other molecules and atoms and slowly build up more complex substances. Sometimes molecules will be destroyed by ultraviolet light from distant stars, but this light can also turn particles into slightly different versions of themselves called <a href="http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/bonding/ionic_bondingrev1.shtml">ions</a>, thereby slowly expanding the range of molecules that can form. </p>
<h2>Soot and fire water</h2>
<p>To make a nine-atom molecule such as ethanol in these cool and tenuous conditions might still take an extremely long time – certainly much longer than the seven days you might ferment home brew in the attic, let alone the time it takes to walk to the liquor store. </p>
<p>But there is help at hand from other simple organic molecules, which start sticking together to form grains of dust, something like soot. On the surfaces of these grains, chemical reactions take place much more rapidly because the molecules get held in proximity to them. </p>
<p>It is therefore cool sooty regions, the potential stellar birthplaces of the future, that encourage complex molecules to appear more quickly. We can tell from the distinctive spectrum lines of different particles in these regions that there is water, carbon dioxide, methane and ammonia – but also plenty of ethanol. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/179199/original/file-20170721-18148-1xqq9en.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179199/original/file-20170721-18148-1xqq9en.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/179199/original/file-20170721-18148-1xqq9en.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=693&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179199/original/file-20170721-18148-1xqq9en.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=693&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179199/original/file-20170721-18148-1xqq9en.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=693&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179199/original/file-20170721-18148-1xqq9en.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=871&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179199/original/file-20170721-18148-1xqq9en.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=871&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179199/original/file-20170721-18148-1xqq9en.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=871&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Room for more!</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/almost-empty-beer-glass-isolated-on-453410167?src=zWSyEpcHcissj_TKI0sNcA-1-76">Africa Studio</a></span>
</figcaption>
</figure>
<p>Now when I say plenty, you have to bear in mind the vastness of the universe. And we are still only <a href="http://adsabs.harvard.edu/doi/10.1086/168830">talking about</a> roughly one in every 10m atoms and molecules. Suppose you could travel through interstellar space holding a pint glass, scooping up only alcohol as you moved. To collect enough for a pint of beer you would have to travel about half a million light years – much further than the size of our Milky Way. </p>
<p>In short, there are mind-bogglingly vast quantities of alcohol in outer space. But since it is dispersed over truly enormous distances, the drinks companies can rest easy. It will be a cold day on the sun before we figure out how to collect any of it, I’m sorry to say.</p><img src="https://counter.theconversation.com/content/81122/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alexander MacKinnon does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>It’s like one great big distillery up there.Alexander MacKinnon, Senior Lecturer, Astrophysics, University of GlasgowLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/749102017-03-23T18:01:35Z2017-03-23T18:01:35ZNew powerful telescopes allow direct imaging of nascent galaxies 12 billion light years away<figure><img src="https://images.theconversation.com/files/162115/original/image-20170323-25783-1fgo3vq.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression of a quasar shining through a galaxy's 'super halo' of hydrogen gas.</span> <span class="attribution"><span class="source">A. Angelich (NRAO/AUI/NSF)</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>How does a galaxy like our own Milky Way form? Until now there’s been a lot of inferring involved in answering that question.</p>
<p>The basic story is that gas collects toward the center of roughly spherical “halos” of matter. The gas then cools, condenses, fragments and eventually collapses to form stars. Generations of stars build up the galaxy and with it the production of heavy elements – such as carbon, oxygen and so on – that populate our periodic table and comprise our familiar physical world.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/162105/original/image-20170322-25776-tjaa1.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/162105/original/image-20170322-25776-tjaa1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/162105/original/image-20170322-25776-tjaa1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/162105/original/image-20170322-25776-tjaa1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/162105/original/image-20170322-25776-tjaa1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/162105/original/image-20170322-25776-tjaa1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/162105/original/image-20170322-25776-tjaa1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/162105/original/image-20170322-25776-tjaa1.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Numerical visualizations of the stars in galaxies forming in the early universe.</span>
<span class="attribution"><span class="source">The Eagle Project, Durham University</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Astrophysicists like me have pieced together this picture thanks largely to theoretical research. <a href="http://icc.dur.ac.uk/Eagle/about.php">We run numerical simulations</a> on the world’s largest supercomputers to capture the processes that govern galaxy formation – <a href="http://physics.stackexchange.com/questions/167496/what-happens-during-gravitational-collapse-to-cause-the-formation-of-a-star">gravitational collapse</a>, heating, <a href="https://en.wikipedia.org/wiki/Radiative_cooling">radiative cooling</a> – at high fidelity.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/162107/original/image-20170322-25783-y93wje.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/162107/original/image-20170322-25783-y93wje.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/162107/original/image-20170322-25783-y93wje.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/162107/original/image-20170322-25783-y93wje.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/162107/original/image-20170322-25783-y93wje.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/162107/original/image-20170322-25783-y93wje.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/162107/original/image-20170322-25783-y93wje.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/162107/original/image-20170322-25783-y93wje.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Numerical simulation of gas corresponding to the same region as the previous figure. Young galaxies are dominated by gas and not stars.</span>
<span class="attribution"><span class="source">The Eagle Project, Durham University</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>To study many of these processes, we were largely restricted to this kind of theoretical inquiry because we didn’t have the technical capacity to observe them. But things have changed as we’ve witnessed the rise of what we consider the “Great Observatories”: NASA’s <a href="https://www.nasa.gov/mission_pages/hubble/story/index.html">Hubble Space Telescope</a>, the twin 10m <a href="http://www.keckobservatory.org/">Keck Telescopes</a> on Manua Kea, Hawaii, and, most recently, the <a href="https://public.nrao.edu/telescopes/alma">Atacama Large Millimeter/submillimeter Array</a> (ALMA) in northern Chile. With these facilities, astronomers have sought to test and refine the tenets of galaxy formation theory, especially the processes governing galaxy assembly and star formation.</p>
<p><a href="http://science.sciencemag.org/cgi/doi/10.1126/science.aal1737">The new data</a> our group is publishing based on observations from ALMA are truly transformative relative to previous observations. They allow us to directly image the gas in nascent galaxies – something that was impossible before – and thereby test our fundamental predictions of galaxy formation.</p>
<h2>The physical challenge</h2>
<p>When we try to directly observe distant galaxies, the principal challenge is the very faint signal that reaches Earth from such great distances. The light from the two galaxies studied in our publication, for example, has traveled 12 billion light years to get here. This also means the light was emitted 12 billion years ago, when the universe was only 1.5 billion years old and galaxies were mere adolescents. And I’m especially interested in studying the gas that fuels star formation, which is particularly difficult to detect.</p>
<p>To address this challenge, starting in 1986 our group – led by <a href="http://dx.doi.org/10.1063/PT.3.2558">the late Arthur M. Wolfe</a> – relied on an indirect way to study distant galaxies. Rather than focusing on the galaxies themselves, we recorded the light from quasars that are even farther away from us. This allows us to probe gas in foreground galaxies.</p>
<p><a href="http://www.space.com/17262-quasar-definition.html">Quasars</a> are exceedingly bright objects that are powered by supermassive black holes. As a quasar’s light travels through the galactic gas we’re actually interested in, the atoms in the gas scatter a small portion of the light <a href="https://theconversation.com/explainer-seeing-the-universe-through-spectroscopic-eyes-37759">at well-defined wavelengths</a>. It’s these so-called <a href="http://astronomy.swin.edu.au/cosmos/A/Absorption+Line">absorption signatures</a> in the quasar’s spectrum that we focus on. The gas is imprinting its signature on the light we can collect with our telescopes. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/162259/original/image-20170323-4948-9dhkv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/162259/original/image-20170323-4948-9dhkv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/162259/original/image-20170323-4948-9dhkv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/162259/original/image-20170323-4948-9dhkv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/162259/original/image-20170323-4948-9dhkv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/162259/original/image-20170323-4948-9dhkv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/162259/original/image-20170323-4948-9dhkv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/162259/original/image-20170323-4948-9dhkv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Light from a distant quasar passes through intervening gas clouds in galaxies and in intergalactic space. These clouds of primeval hydrogen subtract specific colors from the beam. The resulting ‘absorption spectrum’ can help determine the distances and chemical composition of the invisible clouds.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Cumulative-absorption-spectrum-hubble-telescope.jpg">NASA/STScI</a></span>
</figcaption>
</figure>
<p>We pass the light our telescope gathers through a <a href="http://coolcosmos.ipac.caltech.edu/ask/291-What-is-a-spectrometer-">spectrometer</a>, an instrument that allows us to study the brightness as a function of wavelength. Then we can infer that there is in fact gas present between us and the quasar and we can quantitatively measure various properties of the gas. </p>
<p>Arthur used spectrometers at the primary observing suite of the <a href="https://www.ucolick.org/">University of California Observatories</a>, first instruments on the <a href="https://www.ucolick.org/public/telescopes/shane.html">Shane 3m</a> telescope of the Lick Observatory and then, upon being commissioned, led research on the powerful Keck telescopes. These data <a href="http://doi.org/10.1146/annurev.astro.42.053102.133950">provide estimates</a> on the gas surface density, heavy element enrichment, molecular content and dynamical motions of the galaxy. </p>
<p>This observational experiment, however, is limited. It offers little information on the galaxy’s mass, size or star formation – all things that are fundamental to a galaxy’s makeup. It is critical that we measure these properties to understand the formation history of galaxies like our Milky Way. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/162112/original/image-20170323-25751-ar820.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/162112/original/image-20170323-25751-ar820.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/162112/original/image-20170323-25751-ar820.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=403&fit=crop&dpr=1 600w, https://images.theconversation.com/files/162112/original/image-20170323-25751-ar820.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=403&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/162112/original/image-20170323-25751-ar820.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=403&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/162112/original/image-20170323-25751-ar820.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=507&fit=crop&dpr=1 754w, https://images.theconversation.com/files/162112/original/image-20170323-25751-ar820.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=507&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/162112/original/image-20170323-25751-ar820.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=507&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Atacama Large Millimeter/submillimeter Array is made up of 66 antennas, all pointed at the sky collecting data 24 hours a day.</span>
<span class="attribution"><a class="source" href="http://www.almaobservatory.org/en/visuals/images/antennas-and-transporters">ESO/B. Tafreshi (twanight.org)</a></span>
</figcaption>
</figure>
<h2>Next-generation observations</h2>
<p>In 2003, we reported that the then-future <a href="http://iopscience.iop.org/article/10.1086/376520/meta">ALMA telescope would be a true game-changer</a> by enabling us to directly image the gas within nascent galaxies. We would have to wait over a decade to begin while the telescope was built – so we had plenty of time to carefully identify the optimal targets and refine our observing strategies.</p>
<p>All the waiting and planning have now paid off. Arthur’s last Ph.D. student, Marcel Neeleman, <a href="http://science.sciencemag.org/cgi/doi/10.1126/science.aal1737">just published our first results with ALMA</a> and the data are spectacular. Here, in contrast to our previous work, we measure light from the gas in the galaxy itself, which reveals the size and shape of the star-forming regions. And what we saw was not what we expected.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/162114/original/image-20170323-25751-2uzio2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/162114/original/image-20170323-25751-2uzio2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/162114/original/image-20170323-25751-2uzio2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/162114/original/image-20170323-25751-2uzio2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/162114/original/image-20170323-25751-2uzio2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/162114/original/image-20170323-25751-2uzio2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/162114/original/image-20170323-25751-2uzio2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/162114/original/image-20170323-25751-2uzio2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Map of one galaxy’s emission from ionized carbon, taken with the ALMA telescope. These data reveal and resolve the star-forming regions within young, forming galaxies.</span>
<span class="attribution"><span class="source">Neeleman et al doi: 10.1126/science.aal1737</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>ALMA collects light at wavelengths not visible to the human eye. We focused on two sources in our target galaxies: ionized carbon and warm dust, both of which surround the birthplace of new stars. We were able to create maps based on the light emitted by ionized carbon within a galaxy that we first detected in absorption, via our old technique. </p>
<p>Remarkably, the dense, star-forming gas of the galaxy is greatly offset from the hydrogen gas originally revealed by the quasar spectrum (by approximately 100,000 light years or 30 kiloparsecs). This distance shows that young galaxies are surrounded by a massive reservoir of un-ionized, neutral gas. We further suggest that the gas detected in absorption is likely to accrete back onto the galaxy and fuel future generations of stars.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/162207/original/image-20170323-4961-16i99j5.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/162207/original/image-20170323-4961-16i99j5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/162207/original/image-20170323-4961-16i99j5.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=286&fit=crop&dpr=1 600w, https://images.theconversation.com/files/162207/original/image-20170323-4961-16i99j5.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=286&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/162207/original/image-20170323-4961-16i99j5.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=286&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/162207/original/image-20170323-4961-16i99j5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=359&fit=crop&dpr=1 754w, https://images.theconversation.com/files/162207/original/image-20170323-4961-16i99j5.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=359&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/162207/original/image-20170323-4961-16i99j5.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=359&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Spectral image of one galaxy’s light. Horizontal axis describes the size of the galaxy and the vertical axis describes the motion of the gas. Analysis of the image reveals the gas is rotating in a disk, like our own spiral galaxy.</span>
<span class="attribution"><span class="source">Neeleman et al doi: 10.1126/science.aal1737</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The ALMA data also uniquely resolve the internal motions of the galaxy’s gas. Our analysis of the dynamics indicates the gas is configured in a large disk – similar to our Milky Way – and rotating with a speed of approximately 120 km/s. This speed is characteristic of what theory predicts for the progenitors of this sort of galaxy. </p>
<p>Lastly, we detected emission from “warm” dust in the galaxy. (Of course, warm is relative – in this case only about 30 degrees Celsius above absolute zero.) We believe the dust is heated by young massive stars; we estimate that the galaxy is forming stars at a rate of over 100 suns per year, a prodigious and precocious rate. </p>
<p>These data demonstrate the power and potential of ALMA to discover and dissect the progenitors of galaxies like our own. They will be invaluable to refine our understanding – in space and time – of the build-up of galaxies.</p>
<figure>
<iframe src="https://player.vimeo.com/video/209248385" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">Milky Way-like galaxies in the early universe.</span></figcaption>
</figure>
<p>While many of us in the community held some reservations about ALMA (given its great cost), it is now clear to me the payoff will be extraordinary. ALMA research has already paid off in the discovery of <a href="http://www.almaobservatory.org/en/press-room/press-releases/937-almas-best-image-yet-of-a-protoplanetary-disk">protoplanetary disks</a> from which planets form and unlocked hidden secrets of the process of <a href="http://www.almaobservatory.org/en/about-alma/science-with-alma/star-and-planet-formation">star formation</a>. And ALMA will continue to greatly advance our understanding of how galaxies like the Milky Way form.</p>
<hr>
<p><em>Editor’s note: On May 20, 2020, the author and colleagues published <a href="https://doi.org/10.1038/s41586-020-2276-y">new research in the journal Nature</a> that used sharper images from the ALMA telescope to reveal that one galaxy is a rapidly rotating disk galaxy. It’s remarkably similar to our own Milky Way despite its very young age. They named this galaxy the Wolfe Disk in honor of the scientific contributions of Arthur Wolfe and his prediction that such galaxies would exist.</em></p><img src="https://counter.theconversation.com/content/74910/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>J. Xavier Prochaska receives funding from the National Science Foundation.</span></em></p>Astronomers are surprised by what they’re finding out about galaxies that formed in the early days of our universe, now that sensitive telescopes allow direct observation, not the inference of old.J. Xavier Prochaska, Professor of Astronomy & Astrophysics, University of California, Santa CruzLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/648872016-11-27T19:14:29Z2016-11-27T19:14:29ZA Galah to help capture millions of rainbows to map the history of the Milky Way<figure><img src="https://images.theconversation.com/files/140875/original/image-20161007-21447-t8o7h5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Untangling the history of the Milky Way.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:ESO_-_Milky_Way.jpg">ESO/S Brunier</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Our galaxy, the Milky Way, contains at least 100 billion stars. Over the centuries, astronomers have scoured the skies, developing a <a href="https://map.gsfc.nasa.gov/universe/rel_stars.html">thorough understanding of the lives of those stars</a>, from their <a href="http://earthsky.org/space/orion-nebula-jewel-in-orions-sword">formation in vast nebulae</a> to their <a href="http://www.abc.net.au/news/2016-01-15/newly-discovered-supernova-most-powerful-explosion-ever-seen/7086138">fiery and spectacular deaths</a>.</p>
<p>But how has our galaxy changed over time? Where did the stars we see today form, and which of them are siblings, formed together from the same cloud of material? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The lives of stars.</span>
<span class="attribution"><span class="source">Wikimedia/cmglee/NASA Goddard Space Flight Center</span></span>
</figcaption>
</figure>
<p>To answer these questions we need to perform <a href="https://www.aao.gov.au/public/galactic-archaeology">Galactic archaeology</a>. To do this, an ambitious Australian-led observing survey, called <a href="https://galah-survey.org/">Galah</a>, is undertaking the immense task of capturing millions of rainbows to disentangle our galaxy’s story.</p>
<h2>Birds of a feather</h2>
<p>When we break the light from a star into its component colours, the spectrum is laced with dark lines. These are the telltale fingerprints of the various atomic and molecular species present in the star’s outer layers.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=176&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=176&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=176&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=221&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=221&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=221&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Fraunhofer lines - absorption lines in the sun’s spectrum that signpost the chemical composition of its outer atmosphere.</span>
<span class="attribution"><span class="source">Wikimedia/nl:Gebruiker:MaureenV/Phrood/Saperaud</span></span>
</figcaption>
</figure>
<p>By studying those lines we can <a href="http://spiff.rit.edu/classes/phys230/lectures/spec_interp/spec_interp.html">learn a great deal about the star</a>, such as how fast it spins, its temperature, and what elements it is made of. We can even use them to <a href="https://theconversation.com/what-the-weather-is-like-on-a-star-can-help-in-the-search-for-life-56275">study stellar magnetic fields</a>.</p>
<p>In essence, stars turn hydrogen and helium into heavier elements. When they die, they return that material to the galaxy, to be incorporated in the next generation of stars. </p>
<p>Most stars form in <a href="http://www.atnf.csiro.au/outreach/education/senior/astrophysics/stellarevolution_clusters.html">clusters</a>, groups of hundreds to millions of stars that <a href="http://www.atnf.csiro.au/outreach/education/senior/astrophysics/stellarevolution_formation.html">form at the same time in a vast nebula</a>. Each nebula will have a unique composition, seeded by the death throes of the previous generation of stars in the distant past. </p>
<p>We also know that different types of stars return different elements to the galaxy at the end of their lifetimes. Because of this, astronomers can use the elemental patterns in present-day stars to explore what kinds of stars were in our galaxy in the past.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When a star like the Sun comes to the end of its life, it blows off its outer layers to form a planetary nebula – ejecting gas that will form the next generation of stars. The Helix nebula (pictured) is one of the finest examples in the night sky.</span>
<span class="attribution"><span class="source">NASA, ESA, and C R O'Dell (Vanderbilt University)</span></span>
</figcaption>
</figure>
<p>On timescales of millions of years, stars escape from the clusters in which they formed and migrate around the disk of the galaxy.</p>
<p>If we can use spectra to measure the compositions of many stars, we should be able to identify those that are made of the same stuff. The common origins of widely scattered stars is thus revealed by their matching compositions.</p>
<p>That brings us to <a href="http://galah-survey.org">Galah</a>.</p>
<h2>Hatching the idea for Galah</h2>
<p>Galactic archaeology with <a href="https://www.aao.gov.au/science/instruments/current/HERMES">HERMES</a> (<a href="http://galah-survey.org">Galah</a>) is a massive observational project using the <a href="https://www.aao.gov.au/about-us/anglo-australian-telescope">3.9-metre Anglo-Australian Telescope</a> at <a href="http://www.sidingspringobservatory.com.au/">Siding Spring Observatory</a>. Since its start, in late 2013, the survey has collected more than 250,000 spectra, and that number grows every month. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/3ZV7c9xBFuM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Each red and blue point shows an individual GALAH target, with the blue as dwarfs and red as giants.</span></figcaption>
</figure>
<p>To make such a large project possible, Galah uses robots to position fibre optic cables to catch starlight. These allow the <a href="https://galah-survey.org/members">Galah team</a> to observe around 350 stars simultaneously in a region of sky four times the diameter of the full Moon.</p>
<p>After about an hour staring at one group of stars, Galah moves on, scanning field after field to build its catalogue of stellar spectra. When the project is complete, more than a million rainbows will be caught, each <a href="https://galah-survey.org/survey_design">in exquisite detail</a>.</p>
<h2>In good company</h2>
<p>The past few years have seen a worldwide boom in galactic archaeology. Several survey projects are going on around the globe, each filling a unique niche, and even larger projects are planned for the future. </p>
<p>While each of these surveys has a particular goal, when brought together they form a scientific superset that is greater than the sum of its parts. </p>
<p>The <a href="https://www.sdss3.org/surveys/apogee.php">APOGEE survey</a> studies red giant stars throughout the Milky Way using the 3.5-metre Sloan telescope in the United States. </p>
<p>Because it observes at infrared wavelengths, it is the only large survey that can peer through the dust that pervades our galaxy. This allows APOGEE to collect data on stars across the entire galaxy.</p>
<p>The disk of our galaxy, which contains the great majority of stars, is surrounded by a roughly spherical halo which consists of ancient stars. The halo hosts the mysterious globular clusters – spherical swarms of millions of tightly packed stars. </p>
<p>The <a href="https://www.gaia-eso.eu/">Gaia-ESO Survey</a> targets <a href="https://dept.astro.lsa.umich.edu/ugactivities/Labs/MWgalStruct/index.html">all these populations and more</a>, using two different visible-light instruments at the 8-metre Very Large Telescope in Chile.</p>
<p><a href="https://galah-survey.org/">Galah</a>, by contrast, focuses mainly our galaxy’s disk, where the great bulk of its stars reside. By obtaining such a huge sample of stellar spectra, Galah is the perfect complement to these two more focused surveys, providing the context in which their results can be understood. </p>
<h2>Flying to the future with Gaia</h2>
<p>While Galah and its fellow archaeological surveys have been farming the night sky, the <a href="https://theconversation.com/how-were-helping-the-gaia-mission-map-a-billion-stars-to-unparalleled-precision-65602">Gaia</a> spacecraft has been busy pulling together a different, but complementary, data set. </p>
<p>Launched in 2013 on an initial five-year mission, Gaia is continually scouring the sky, repeatedly observing more than a billion stars, measuring their positions with unprecedented precision. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=532&fit=crop&dpr=1 600w, https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=532&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=532&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=668&fit=crop&dpr=1 754w, https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=668&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=668&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The motion of Barnard’s star, one of the sun’s nearest neighbours, against background stars over a 20 year period.</span>
<span class="attribution"><span class="source">Steve Quirk</span></span>
</figcaption>
</figure>
<p>By observing the same star several times, Gaia can determine how it moves across the sky, giving us an incredibly <a href="http://www.astronomy.ohio-state.edu/%7Epogge/Ast162/Unit1/distances.html">precise measurement of the star’s distance from Earth</a>. Gaia also reveals <a href="http://www.atnf.csiro.au/outreach/education/senior/astrophysics/proper_motion.html">the kinematics of the stars</a> – how they move with respect to one another through our galaxy.</p>
<p>Even on its own, Gaia’s data will be an incredible resource. But when combined with data obtained by Galah and its siblings, it becomes far more powerful. Gaia will provide the distance to, and the precise motion of, a huge number of stars that will also have been surveyed by Galah. </p>
<h2>Our first steps</h2>
<p>The <a href="http://www.cosmos.esa.int/web/gaia/dr1">first public release</a> of Gaia data earlier this year included precise sky positions and brightnesses for more than a billion stars and quasars. More importantly for our work, it also included the distances and space motions for 2 million stars that had been targeted by previous space missions.</p>
<p>To coordinate with Gaia, Galah also made a subset of its data <a href="https://cloudstor.aarnet.edu.au/plus/index.php/s/OMc9QWGG1koAK2D">publicly available</a>, including data for 9,860 stars. Of these, 7,894 are in the special subset released by the Gaia team, and hence have precisely known distances.</p>
<p>Combining these data sets will allow the Galah team to investigate not just which stars formed together, but to examine whether they still follow similar paths around the galaxy. </p>
<p>As the Gaia mission continues, it will provide precise distances and space motions for every single star in the Galah catalogue. By piecing Gaia’s data together with our own, we will paint a far more detailed picture of our galaxy’s past, present and future than has ever been seen before.</p><img src="https://counter.theconversation.com/content/64887/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sarah Martell receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Jonathan P. Marshall and Jonti Horner do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Understanding how the billions of stars in our galaxy formed and evolved is the subject of a huge galactic archaeology project.Jonti Horner, Vice Chancellor's Senior Research Fellow, University of Southern QueenslandJonathan P. Marshall, Vice Chancellor's Post-doctoral Research Fellow, UNSW SydneySarah Martell, Senior lecturer, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/618542016-07-11T19:38:49Z2016-07-11T19:38:49ZWhy do some galaxies stop making new stars?<figure><img src="https://images.theconversation.com/files/128876/original/image-20160630-30655-18nxf78.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Spiral galaxy NGC 3953 is a veritable star making machine, but why do some galaxies stop forming new stars?</span> <span class="attribution"><a class="source" href="http://www.nsatlas.org/getAtlas.html?search=name&name=ngc+3953&radius=10.0&submit_form=Submit">NASA-Sloan Atlas</a></span></figcaption></figure><p><a href="http://theconversation.com/explainer-a-beginners-guide-to-the-galaxy-49">Galaxies</a> are star-making machines, churning out new stars fuelled by cold gas collapsing under the force of gravity. Some galaxies can produce hundreds of new stars in a single year, and individual galaxies can contain many billions of stars.</p>
<p>Our own galaxy, <a href="https://theconversation.com/is-our-milky-way-galaxy-a-zombie-already-dead-and-we-dont-know-it-52732">the Milky Way</a>, is dotted with star-forming regions. One of these, <a href="http://hubblesite.org/gallery/tours/tour-orion/">the Orion Nebula</a>, is so bright you can see it with <a href="http://www.skyandtelescope.com/observing/celestial-objects-to-watch/observing-the-great-orion-nebula/">the unaided eye</a>. Look at the middle “star” of Orion’s sword, and you are actually seeing stars being born.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/128869/original/image-20160630-30635-1f3dh3t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/128869/original/image-20160630-30635-1f3dh3t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/128869/original/image-20160630-30635-1f3dh3t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/128869/original/image-20160630-30635-1f3dh3t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/128869/original/image-20160630-30635-1f3dh3t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/128869/original/image-20160630-30635-1f3dh3t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/128869/original/image-20160630-30635-1f3dh3t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/128869/original/image-20160630-30635-1f3dh3t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The middle star in Orion’s sword is actually the Orion Nebula, where new stars are being born.</span>
<span class="attribution"><span class="source">NASA, C.R. O'Dell and S.K. Wong (Rice University)</span></span>
</figcaption>
</figure>
<p>But something can break these star-making machines; many <a href="http://astronomy.swin.edu.au/cosmos/E/elliptical+galaxy">elliptical galaxies</a> have stopped forming new stars. What stops them is one of the biggest questions in astronomy. </p>
<h2>Breaking the machines</h2>
<p>A distinctive feature of elliptical galaxies is their ellipsoidal shapes, much like an Aussie rules or rugby ball. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/128870/original/image-20160630-30642-1x5u9xi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/128870/original/image-20160630-30642-1x5u9xi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/128870/original/image-20160630-30642-1x5u9xi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=436&fit=crop&dpr=1 600w, https://images.theconversation.com/files/128870/original/image-20160630-30642-1x5u9xi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=436&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/128870/original/image-20160630-30642-1x5u9xi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=436&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/128870/original/image-20160630-30642-1x5u9xi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=548&fit=crop&dpr=1 754w, https://images.theconversation.com/files/128870/original/image-20160630-30642-1x5u9xi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=548&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/128870/original/image-20160630-30642-1x5u9xi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=548&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Many elliptical galaxies have effectively stopped making new stars.</span>
<span class="attribution"><span class="source">NASA Sloan Atlas</span></span>
</figcaption>
</figure>
<p>The Milky Way, and many other large star-forming galaxies, are <a href="http://astronomy.swin.edu.au/cosmos/S/Spiral+Galaxy">spiral galaxies</a>. In spiral galaxies, stars and the gaseous fuel to make new stars circle around the galaxy in a vast flat disk.</p>
<p>Does the formation of new stars critically depend on galaxy shape? It seems plausible given most spiral galaxies are forming stars and most elliptical galaxies aren’t. </p>
<p>But how then do elliptical galaxies grow? Back in 1972, the brothers <a href="https://ned.ipac.caltech.edu/level5/Toomre/Toomre_contents.html">Alar and Juri Toomre</a> showed that new elliptical galaxies could be created by merging spiral galaxies together. Indeed, billions of years from now, <a href="http://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html">our own Milky Way will collide with the Andromeda galaxy</a> to create a new elliptical galaxy. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/fMNlt2FnHDg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The collision of the Milky Way with the Andromeda galaxy will form a new, elliptical galaxy.</span></figcaption>
</figure>
<p>Perhaps it is the process of galaxy mergers that breaks star-making machines. But not all plausible mechanisms for stopping star formation clearly depend on galaxy shape. </p>
<p>For example, galaxies ploughing through hot plasma can have star-forming gas stripped from them, but this process shouldn’t transform spiral galaxies into elliptical galaxies. </p>
<p>There are <a href="http://phys.org/news/2011-05-dead-galaxies.html">some elliptical galaxies that are forming stars</a>, but are there any spiral galaxies without any star formation? Is star formation intimately linked to galaxy shape or not? We decided to find out.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/128872/original/image-20160630-30646-18qvcfb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/128872/original/image-20160630-30646-18qvcfb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/128872/original/image-20160630-30646-18qvcfb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=466&fit=crop&dpr=1 600w, https://images.theconversation.com/files/128872/original/image-20160630-30646-18qvcfb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=466&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/128872/original/image-20160630-30646-18qvcfb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=466&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/128872/original/image-20160630-30646-18qvcfb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=585&fit=crop&dpr=1 754w, https://images.theconversation.com/files/128872/original/image-20160630-30646-18qvcfb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=585&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/128872/original/image-20160630-30646-18qvcfb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=585&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Star-forming galaxy NGC 3310 is blue because it contains short-lived hot blue stars.</span>
<span class="attribution"><span class="source">Sloan Digital Sky Survey</span></span>
</figcaption>
</figure>
<h2>Searching for star formation</h2>
<p>How do you find galaxies that are forming stars versus those that are not? Easy. You look for <a href="http://theconversation.com/explainer-what-are-stars-15235">stars</a> that die young. </p>
<p>Our yellowish sun is about halfway through its 10-billion-year life. But very luminous hot blue stars have lifetimes of just 30 million years. </p>
<p>In cosmological terms, 30 million years is a blink of the eye. Find a galaxy with these blue stars, and you are seeing a galaxy forming stars (or that formed stars very recently). Conversely, a red galaxy may not be forming any new stars. </p>
<p>There are other ways of looking for star-forming galaxies too. Hot stars warm the dust within galaxies, and that warm dust glows in <a href="http://coolcosmos.ipac.caltech.edu/page/what_is_infrared">infrared light</a>. Hot stars also cause surrounding gas to glow, producing a distinctive <a href="https://theconversation.com/explainer-seeing-the-universe-through-spectroscopic-eyes-37759">spectrum of light</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/128918/original/image-20160630-30661-tkmxmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/128918/original/image-20160630-30661-tkmxmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/128918/original/image-20160630-30661-tkmxmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=62&fit=crop&dpr=1 600w, https://images.theconversation.com/files/128918/original/image-20160630-30661-tkmxmh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=62&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/128918/original/image-20160630-30661-tkmxmh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=62&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/128918/original/image-20160630-30661-tkmxmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=77&fit=crop&dpr=1 754w, https://images.theconversation.com/files/128918/original/image-20160630-30661-tkmxmh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=77&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/128918/original/image-20160630-30661-tkmxmh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=77&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Glowing hydrogen gas produces a distinctive spectrum of light.</span>
<span class="attribution"><span class="source">Jan Homann/Wikipedia</span></span>
</figcaption>
</figure>
<h2>Red and dead?</h2>
<p>We weren’t the first to look for spiral galaxies that aren’t forming stars. In 1976, Canadian astronomer <a href="http://gruber.yale.edu/cosmology/sidney-van-den-bergh">Sidney van den Bergh</a> found “anaemic” galaxies that have far less star formation than typical spiral galaxies.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/128875/original/image-20160630-30625-1m1aj66.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/128875/original/image-20160630-30625-1m1aj66.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/128875/original/image-20160630-30625-1m1aj66.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=528&fit=crop&dpr=1 600w, https://images.theconversation.com/files/128875/original/image-20160630-30625-1m1aj66.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=528&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/128875/original/image-20160630-30625-1m1aj66.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=528&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/128875/original/image-20160630-30625-1m1aj66.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=664&fit=crop&dpr=1 754w, https://images.theconversation.com/files/128875/original/image-20160630-30625-1m1aj66.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=664&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/128875/original/image-20160630-30625-1m1aj66.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=664&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sidney van den Bergh identified NGC 718 as an anaemic spiral galaxy, with just a trickle of star formation.</span>
<span class="attribution"><span class="source">Sloan Digital Sky Survey</span></span>
</figcaption>
</figure>
<p>And British astronomer <a href="http://icg.port.ac.uk/%7Emastersk/">Karen Masters</a> has identified thousands of red spiral galaxies using the citizen science <a href="https://theconversation.com/beyond-todays-crowdsourced-science-to-tomorrows-citizen-science-cyborgs-53904">GalaxyZoo Project</a>.</p>
<p>But the spectra of red spiral galaxies identified by van den Bergh and Masters show the distinctive glow of hydrogen gas surrounding hot blue stars. These galaxies must still be forming new stars. </p>
<p>We decided to take a different approach to finding spiral galaxies without star formation, utilising images from NASA’s <a href="http://www.jpl.nasa.gov/wise/">Wide-field Infrared Survey Explorer</a>. </p>
<p>We searched for spiral galaxies without the infrared glow of warm dust heated by short-lived hot blue stars. The galaxies we found turned out to be red in ultraviolet and visible light, as expected if they aren’t forming new stars.</p>
<p>To be totally sure these spiral galaxies are truly dead, we decided to obtain their <a href="http://theconversation.com/explainer-seeing-the-universe-through-spectroscopic-eyes-37759">spectra</a>, using the <a href="http://rsaa.anu.edu.au/observatories/telescopes/anu-23m-telescope">Siding Spring 2.3-metre telescope</a>, near Coonabarabran in New South Wales. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/128880/original/image-20160630-30642-wdlllj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/128880/original/image-20160630-30642-wdlllj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/128880/original/image-20160630-30642-wdlllj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/128880/original/image-20160630-30642-wdlllj.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/128880/original/image-20160630-30642-wdlllj.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/128880/original/image-20160630-30642-wdlllj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/128880/original/image-20160630-30642-wdlllj.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/128880/original/image-20160630-30642-wdlllj.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">We used the Siding Spring 2.3-metre telescope to search for glowing hydrogen gas.</span>
<span class="attribution"><span class="source">Ssopete/Wikipedia</span></span>
</figcaption>
</figure>
<p>None of the six spectra had the distinctive signature of glowing gas heated by short-lived stars. We had finally found spiral galaxies that aren’t forming stars. </p>
<p>Our letter announcing this discovery was recently accepted for publication in <a href="http://adsabs.harvard.edu/abs/2016arXiv160603781F">Monthly Notices of the Royal Astronomical Society</a>. </p>
<h2>So what stops star formation?</h2>
<p>Clearly, star formation can be turned off without transforming spiral galaxies into elliptical galaxies. But just what is stopping star formation? There are several possibilities.</p>
<p>One option is <a href="https://astrobites.org/2013/03/13/ram-pressure-stripping-a-classic-paper/">ram pressure stripping</a>, where gas is stripped from a galaxy plunging through hot plasma. But this process should only work in <a href="https://theconversation.com/giant-galaxies-die-from-the-inside-when-they-stop-making-stars-40310">clusters of galaxies</a>, and many of our galaxies aren’t in galaxy clusters. </p>
<p>Perhaps gas cannot cool to produce new stars because of <a href="https://ned.ipac.caltech.edu/level5/Sept13/Silk/Silk8.html">heating by active galactic nuclei</a>, which are powered by the in-fall of matter towards enormous black holes. This may be true in some instances, but we didn’t see evidence for active galactic nuclei in most of our galaxies.</p>
<p>We now have a new mystery on our hands. What stops star formation in these unusual spiral galaxies?</p>
<p>Funnily enough, galaxy shapes may provide a clue. The British astronomer Karen Masters finds that spiral galaxies with little star formation often feature prominent “<a href="https://blog.galaxyzoo.org/2015/03/20/whats-all-the-fuss-about-bars-in-galaxies/">bars</a>” straddling their centres. This also seems to be true for spiral galaxies without star formation. Perhaps galaxy shape plays a critical role breaking star-making machines after all. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/128871/original/image-20160630-30664-17vdafq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/128871/original/image-20160630-30664-17vdafq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/128871/original/image-20160630-30664-17vdafq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=355&fit=crop&dpr=1 600w, https://images.theconversation.com/files/128871/original/image-20160630-30664-17vdafq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=355&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/128871/original/image-20160630-30664-17vdafq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=355&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/128871/original/image-20160630-30664-17vdafq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=446&fit=crop&dpr=1 754w, https://images.theconversation.com/files/128871/original/image-20160630-30664-17vdafq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=446&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/128871/original/image-20160630-30664-17vdafq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=446&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">NGC 4440, like many spiral galaxies with little or no star formation, features a distinctive bar straddling its centre.</span>
<span class="attribution"><span class="source">Sloan Digital Sky Survey</span></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/61854/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael J. I. Brown receives research funding from the Australian Research Council and Monash University, and has developed space-related titles for Monash University's MWorld educational app.
</span></em></p><p class="fine-print"><em><span>Amelia Fraser-McKelive is the recipient of an Australian Postgraduate Award and receives funding for her research from Monash University.</span></em></p><p class="fine-print"><em><span>Kevin Pimbblet receives research funding from the University of Hull. He is affiliated with Monash University as an adjunct academic. </span></em></p>Galaxies are supposed to be the place where new stars are formed. So what causes some to stop this stellar production line?Michael J. I. Brown, Associate professor, Monash UniversityAmelia Fraser-McKelvie, PhD student in observational astronomy, Monash UniversityKevin Pimbblet, Senior Lecturer in Physics, University of HullLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/527322016-01-28T10:46:32Z2016-01-28T10:46:32ZIs our Milky Way galaxy a zombie, already dead and we don’t know it?<figure><img src="https://images.theconversation.com/files/109408/original/image-20160127-26823-vlapaf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Can a galaxy (like NGC 3810 in this case) have a classical spiral structure and also be already dead?</span> <span class="attribution"><a class="source" href="https://www.spacetelescope.org/images/potw1006a/">ESA/Hubble and NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Like a zombie, the Milky Way galaxy may already be dead but it still keeps going. Our galactic neighbor Andromeda almost certainly expired a few billion years ago, but only recently started showing outward signs of its demise.</p>
<p>Galaxies seem to be able to “perish” – that is, stop turning gas into new stars – via two very different pathways, driven by very different processes. Galaxies like the Milky Way and Andromeda do so very, very slowly over billions of years. </p>
<p>How and why galaxies “quench” their star formation and change their morphology, or shape, is one of the big questions in extragalactic astrophysics. We may now be on the brink of being able to piece together how it happens. And part of the thanks goes to citizen scientists who combed through millions of galactic images to classify what’s out there.</p>
<h2>Galaxies grow by making new stars</h2>
<p>Galaxies are dynamic systems that continually accrete gas and convert some of it into stars.</p>
<p>Like people, galaxies need food. In the case of galaxies, that “food” is a supply of fresh hydrogen gas from the cosmic web, the filaments and halos of dark matter that make up the largest structures in the universe. As this gas <a href="http://www.illustris-project.org/media/">cools and falls into dark matter halos</a>, it turns into a disk that then can cool even further and eventually fragment into stars.</p>
<p>As stars age and die, they can return some of that gas back into the galaxy either via winds from stars or by <a href="https://en.wikipedia.org/wiki/Supernova">going supernova</a>. As massive stars die in such explosions, they heat the gas around them and prevent it from cooling down quite so fast. They provide what astronomers call “feedback”: star formation in galaxies is thus a self-regulated process. The heat from dying stars means cosmic gas doesn’t cool into new stars as readily, which ultimately puts a brake on how many new stars can form. </p>
<p>Most of these star-forming galaxies are disk- or spiral-shaped, like our Milky Way.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/107855/original/image-20160111-6961-1cp7xoq.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/107855/original/image-20160111-6961-1cp7xoq.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/107855/original/image-20160111-6961-1cp7xoq.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=304&fit=crop&dpr=1 600w, https://images.theconversation.com/files/107855/original/image-20160111-6961-1cp7xoq.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=304&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/107855/original/image-20160111-6961-1cp7xoq.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=304&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/107855/original/image-20160111-6961-1cp7xoq.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=381&fit=crop&dpr=1 754w, https://images.theconversation.com/files/107855/original/image-20160111-6961-1cp7xoq.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=381&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/107855/original/image-20160111-6961-1cp7xoq.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=381&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Left: a spiral galaxy ablaze in the blue light of young stars from ongoing star formation; right: an elliptical galaxy bathed in the red light of old stars.</span>
<span class="attribution"><a class="source" href="http://www.sdss3.org/">Sloan Digital Sky Survey</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>But there’s another kind of galaxy that has a very different shape, or morphology, in astronomer-parlance. These massive elliptical galaxies tend to look spheroidal or football-shaped. They’re not nearly so active – they’ve lost their supply of gas and therefore have ceased forming new stars. Their stars move on far more unordered orbits, giving them their bulkier, rounder shape.</p>
<p>These elliptical galaxies differ in two major ways: they no longer form stars and they have a different shape. Something pretty dramatic must have happened to them to produce such profound changes. What?</p>
<h2>Blue=young and red=old?</h2>
<p>The basic division of galaxies into star-forming spiral galaxies blazing in the blue light of massive, young and short-lived stars, on the one hand, and quiescent ellipticals bathed in the warm glow of ancient low-mass stars, on the other, goes back to early galaxy surveys of the 20th century.</p>
<p>But, once modern surveys like the Sloan Digital Sky Survey (<a href="http://www.sdss.org/">SDSS</a>) began to record hundreds of thousands of galaxies, objects started emerging that didn’t quite fit into those two broad categories. </p>
<p>A significant number of red, quiescent galaxies aren’t elliptical in shape at all, but retain roughly a disk shape. Somehow, these galaxies stopped forming stars without dramatically changing their structure.</p>
<p>At the same time, blue elliptical galaxies started to surface. Their structure is similar to that of “red and dead” ellipticals, but they shine in the bright blue light of young stars, indicating that star formation is still ongoing in them.</p>
<p>How do these two oddballs – the red spirals and the blue ellipticals – fit into our picture of galaxy evolution?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/107856/original/image-20160111-6992-18qgpso.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/107856/original/image-20160111-6992-18qgpso.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/107856/original/image-20160111-6992-18qgpso.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=423&fit=crop&dpr=1 600w, https://images.theconversation.com/files/107856/original/image-20160111-6992-18qgpso.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=423&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/107856/original/image-20160111-6992-18qgpso.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=423&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/107856/original/image-20160111-6992-18qgpso.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=532&fit=crop&dpr=1 754w, https://images.theconversation.com/files/107856/original/image-20160111-6992-18qgpso.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=532&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/107856/original/image-20160111-6992-18qgpso.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=532&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Galaxy Zoo allows citizen scientists to classify galaxies.</span>
<span class="attribution"><span class="source">Screenshot by Kevin Schawinski</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Send in the citizen scientists</h2>
<p>As a graduate student in Oxford, I was looking for some of these oddball galaxies. I was particularly interested in the blue ellipticals and any clues they contained about the formation of elliptical galaxies in general.</p>
<p>At one point, I spent a whole week going through almost 50,000 galaxies from SDSS by eye, as none of the available algorithms for classifying galaxy shape was as good as I needed it to be. I found quite a few blue ellipticals, but the value of classifying all of the roughly one million galaxies in SDSS with human eyes quickly became apparent. Of course, going through a million galaxies by myself wasn’t possible.</p>
<p>A short time later, a group of collaborators and I launched <a href="galaxyzoo.org">galaxyzoo.org</a> and invited members of the public – citizen scientists – to participate in astrophysics research. When you logged on to Galaxy Zoo, you’d be shown an image of a galaxy and a set of buttons corresponding to possible classifications, and a tutorial to help you recognize the different classes. </p>
<p>By the time we stopped recording classifications from a quarter-million people, each of the one million galaxies on Galaxy Zoo had been classified over 70 times, giving me <a href="http://doi.org/10.1111/j.1365-2966.2008.13689.x">reliable, human classifications of galaxy shape</a>, including a measure of uncertainty. Did 65 out of 70 citizen scientists agree that this galaxy is an elliptical? Good! If there’s no agreement at all, that’s information too.</p>
<p>Tapping into the “wisdom of the crowd” effect coupled with the unparalleled human ability for pattern recognition helped sort through a million galaxies and unearthed many of the less common blue ellipticals and red spirals for us to study.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/109405/original/image-20160127-26823-1ia00a4.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/109405/original/image-20160127-26823-1ia00a4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/109405/original/image-20160127-26823-1ia00a4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/109405/original/image-20160127-26823-1ia00a4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/109405/original/image-20160127-26823-1ia00a4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/109405/original/image-20160127-26823-1ia00a4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/109405/original/image-20160127-26823-1ia00a4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/109405/original/image-20160127-26823-1ia00a4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The galaxy color-mass diagram. Blue, star-forming galaxies are at the bottom, in the blue cloud. Red, quiescent galaxies are at the top, in the red sequence. The ‘green valley’ is the transition zone in between.</span>
<span class="attribution"><span class="source">Schawinski+14</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Unwittingly living in the green valley?</h2>
<p>The crossroads of galaxy evolution is a place called the “<a href="https://en.wikipedia.org/wiki/Galaxy_color%E2%80%93magnitude_diagram">green valley</a>.” This may sound scenic, but refers to the population between the blue star-forming galaxies (the “blue cloud”) and the red, passively evolving galaxies (the “red sequence”). Galaxies with “green” or intermediate colors should be those galaxies in which star formation is in the process of turning off, but which still have some ongoing star formation – indicating the process only shut down a short while ago, perhaps a few hundred million years.</p>
<p>As a curious aside, the origin of the term “green valley” may actually go back to a talk given at the University of Arizona on galaxy evolution where, when the speaker described the galaxy color-mass diagram, a member of the audience called out: “the green valley, where galaxies go to die!” Green Valley, Arizona, is a retirement community just outside of the university’s hometown, Tucson.</p>
<p>For our project, the really exciting moment came when we looked at the <a href="http://doi.org/10.1093/mnras/stu327">rate at which various galaxies were dying</a>. We found the slowly dying ones are the spirals and the rapidly dying ones are the ellipticals. There must be two fundamentally different evolutionary pathways that lead to quenching in galaxies. When we explored these two scenarios – dying slowly, and dying quickly – it became obvious that these two pathways have to be tied to the gas supply that fuels star formation in the first place.</p>
<p>Imagine a spiral galaxy like our own Milky Way merrily converting gas to stars as new gas keeps flowing in. Then something happens that turns off that supply of fresh outside gas: perhaps the galaxy fell into a massive cluster of galaxies where the hot intra-cluster gas cuts off fresh gas from the outside, or perhaps the dark matter halo of the galaxy grew so much that gas falling into it gets shock heated to such a high temperature that it cannot cool down within the age of the universe. In any case, the spiral galaxy is now left with just the gas it has in its reservoir. </p>
<p>Since these reservoirs can be enormous, and the conversion of gas to stars is a very slow process, our spiral galaxy could go on for quite a while looking “alive” with new stars, while the actual rate of star formation declines over several billion years. The glacial slowness of using up the remaining gas reservoir means that by the time we realize that a galaxy is in terminal decline, the “trigger moment” occurred billions of years ago.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/109406/original/image-20160127-26817-1h9dhs2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/109406/original/image-20160127-26817-1h9dhs2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/109406/original/image-20160127-26817-1h9dhs2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=192&fit=crop&dpr=1 600w, https://images.theconversation.com/files/109406/original/image-20160127-26817-1h9dhs2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=192&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/109406/original/image-20160127-26817-1h9dhs2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=192&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/109406/original/image-20160127-26817-1h9dhs2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=241&fit=crop&dpr=1 754w, https://images.theconversation.com/files/109406/original/image-20160127-26817-1h9dhs2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=241&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/109406/original/image-20160127-26817-1h9dhs2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=241&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A Hubble image of part of the Andromeda galaxy, which like our Milky Way may be a galactic zombie.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/content/goddard/hubble-s-high-definition-panoramic-view-of-the-andromeda-galaxy">NASA, ESA, J. Dalcanton, B.F. Williams and L.C. Johnson (University of Washington), the PHAT team, and R. Gendler</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The Andromeda galaxy, our nearest massive spiral galaxy, is in the green valley and likely began its decline eons ago: it is a zombie galaxy, according to our latest research. It’s dead, but keeps on moving, still producing stars, but at a diminished rate compared to what it should if it were still a normal star-forming galaxy. Working out whether the Milky Way is in the green valley – in the process of shutting down – is much more challenging, as we are in the Milky Way and cannot easily measure <a href="http://doi.org/10.1088/0004-637X/736/2/84">its integrated properties</a> the way we can for distant galaxies.</p>
<p>Even with the more uncertain data, it looks like the Milky Way is just at the edge, ready to tumble into the green valley. It’s entirely possible that the Milky Way galaxy is a zombie, having died a billion years ago.</p><img src="https://counter.theconversation.com/content/52732/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kevin Schawinski receives funding from the Swiss National Fund. He is the co-founder of Galaxy Zoo. </span></em></p>Extragalactic astrophysicists want to know how and why galaxies stop forming stars, change their shape and fade away. With help from citizen scientists, they’re figuring it out.Kevin Schawinski, Assistant Professor of Galaxy & Black Hole Astrophysics, Swiss Federal Institute of Technology ZurichLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/483842015-11-03T02:32:18Z2015-11-03T02:32:18ZCold light: astronomers go to the ends of the Earth to see cosmic carbon<figure><img src="https://images.theconversation.com/files/99631/original/image-20151026-18424-cwlw88.jpg?ixlib=rb-1.1.0&rect=93%2C238%2C2562%2C1627&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The edge of the Horsehead nebula, where it touches the empty space outside it, is rich in carbon.</span> <span class="attribution"><a class="source" href="http://www.nasa.gov/mission_pages/hubble/science/horsehead-different.html">NASA, ESA, and the Hubble Heritage Team (STScI/AURA)</a></span></figcaption></figure><p>The <a href="http://www.esrl.noaa.gov/research/themes/carbon/">carbon cycle</a> is central to life on Earth. It describes how carbon flows between living organisms, and the ocean, atmosphere and rock of our planet, and is driven by the energy from our sun.</p>
<p>But a carbon cycle also exists for our galaxy, and astronomers are opening new windows into space that let us watch this galactic <a href="http://soral.as.arizona.edu/HEAT/science/">carbon ecosystem</a> in action.</p>
<p>However, the light from carbon in space can be very hard to see because most of it is blocked by the Earth’s atmosphere. But now a new telescope built in one of the most remote regions of our planet is letting us see cosmic carbon in a new light.</p>
<h2>Game of millimetres</h2>
<p>All elements in the universe emit light with a characteristic fingerprint in the form of <a href="http://physics.ucr.edu/%7Ewudka/Physics7/Notes_www/node107.html">emission lines</a>. So just by teasing apart the spectrum of the light received from space, astronomers can determine what elements are out there.</p>
<p>Interstellar carbon comes in several forms. It is sometimes missing an electron, making it <a href="http://www.bbc.co.uk/bitesize/intermediate2/physics/radioactivity/ionisation/revision/1/">ionised</a>. In this state it emits the brightest single spectral line produced by entire galaxies. </p>
<p>Carbon can also be found in atomic form as single atoms. Such atoms reside in the surfaces of molecular clouds, near to the interfaces with atomic gas. Or the carbon can be incorporated into molecules. Here it is primarily found as carbon monoxide, CO, the second most abundant molecule in the universe after hydrogen in the form of H₂.</p>
<p>Carbon monoxide emits in the <a href="http://ethw.org/Millimeter_Waves">millimetre portion</a> of the electromagnetic spectrum. This can be readily studied, such as by the <a href="https://theconversation.com/scientists-turn-to-crowdfunding-to-save-australias-space-research-from-cutbacks-47107">Mopra telescope in Australia</a>, which is <a href="http://newt.phys.unsw.edu.au/mopraco/">charting a new map</a> of the molecular clouds of our galaxy.</p>
<p>However, water absorbs the wavelengths of light emitted by ionised or atomic carbon, which makes it hard to see it from here on Earth. This means we must use airborne or space telescopes, which is an expensive proposition.</p>
<p>A small amount of terahertz radiation does penetrate to the ground at the driest locations on the Earth’s surface. One example is the high Altiplano of Chile, where the giant <a href="http://www.almaobservatory.org/">ALMA radio telescope</a> is being built. But the transmission is patchy and the signal variable. </p>
<h2>Cold heights</h2>
<p>The very driest and coldest place on Earth surface is the summit of the <a href="https://en.wikipedia.org/wiki/Antarctic_Plateau">Antarctic plateau</a>. Here, through the long darkness of winter, the terahertz windows are opened. But this is a challenging environment to work in, to say the least. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/97889/original/image-20151009-23860-pb2h80.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/97889/original/image-20151009-23860-pb2h80.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/97889/original/image-20151009-23860-pb2h80.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/97889/original/image-20151009-23860-pb2h80.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/97889/original/image-20151009-23860-pb2h80.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/97889/original/image-20151009-23860-pb2h80.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/97889/original/image-20151009-23860-pb2h80.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The astronomical observatory at Ridge A, near the summit of the Antarctic plateau. The yellow box is the PLATO-R instrument module. The HEAT telescope is to the left and the solar cube to right.</span>
<span class="attribution"><span class="source">Craig Kulesa/University of Arizona</span></span>
</figcaption>
</figure>
<p>Two decades of Antarctic development at the University of New South Wales, and three generations of autonomous laboratories have led to PLATO, the PLATeau Observatory. One module is now operating at <a href="http://mcba11.phys.unsw.edu.au/%7Eplato-r/">Ridge A</a> on top of the Antarctic plateau. With our partners at the University of Arizona building a new telescope to go with it, <a href="http://soral.as.arizona.edu/heat/">HEAT, the High Elevation Antarctic Terahertz telescope</a>, we now are able to exploit the spectacularly dry, cold and stable conditions for astronomy.</p>
<p>HEAT can measure the terahertz lines of carbon. The telescope is fixed on the ice and records the signal as the sky rotates about it. HEAT is building up a map of carbon in the galaxy in strips, “day” by “day”. </p>
<p>After two years of mapping the team have produced the <a href="http://adsabs.harvard.edu/abs/2014ApJ...782...72B">first</a> high resolution <a href="http://adsabs.harvard.edu/abs/2015ApJ...811...13B">maps</a> of carbon in the galaxy.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/97892/original/image-20151009-23875-1mstr1j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/97892/original/image-20151009-23875-1mstr1j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/97892/original/image-20151009-23875-1mstr1j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/97892/original/image-20151009-23875-1mstr1j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/97892/original/image-20151009-23875-1mstr1j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/97892/original/image-20151009-23875-1mstr1j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/97892/original/image-20151009-23875-1mstr1j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Craig Kulesa hard at work on the HEAT terahertz telescope at Ridge A near to the 4,000m summit of the Antarctic plateau.</span>
<span class="attribution"><span class="source">Craig Kulesa/University of Arizona</span></span>
</figcaption>
</figure>
<p>These maps need to be compared to other species in the interstellar medium. We use the <a href="https://www.narrabri.atnf.csiro.au/mopra/">Mopra</a> telescope to see carbon monoxide. And the <a href="http://www.parkes.atnf.csiro.au/">Parkes</a> and Australia Telescope Compact Array (<a href="https://www.narrabri.atnf.csiro.au/">ATCA</a>) for <a href="http://www.atnf.csiro.au/research/HI/sgps/queryForm.html/">atomic hydrogen</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/97882/original/image-20151009-23860-101t462.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/97882/original/image-20151009-23860-101t462.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=305&fit=crop&dpr=1 600w, https://images.theconversation.com/files/97882/original/image-20151009-23860-101t462.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=305&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/97882/original/image-20151009-23860-101t462.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=305&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/97882/original/image-20151009-23860-101t462.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=383&fit=crop&dpr=1 754w, https://images.theconversation.com/files/97882/original/image-20151009-23860-101t462.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=383&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/97882/original/image-20151009-23860-101t462.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=383&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Carbon monoxide measured by the Mopra telescope is in the top row (blue & red), carbon measured by the HEAT telescope in Antarctica is in green and the atomic hydrogen measured by the Parkes and ATCA telescopes is in yellow.</span>
<span class="attribution"><span class="source">Michael Burton/UNSW</span></span>
</figcaption>
</figure>
<p>Using these tools we have been able to see where clouds of atomic carbon transition into clouds to molecular carbon. In one location, a filamentary molecular cloud over 200 light years in extent but no more than 10 light years across appears to be condensing out of a surrounding atomic substrate. </p>
<p>No clear sign of star formation is seen in this cloud. Its gas is incredibly cold and quiescent. It could be the first molecular cloud to be seen still in the process of formation.</p>
<p>We are also beginning to learn about a new component of the interstellar medium: the dark molecular gas. Here carbon exists but carbon monoxide is absent. Perhaps one-third of the molecular gas resides in this dark form.</p>
<p>One major element is still missing from this puzzle: the contribution from ionised carbon, because its emission occurs in an even harder part of the terahertz window to monitor. The next stage in our venture will open that window. </p>
<p>The USA will launch a <a href="http://soral.as.arizona.edu/STO/Welcome.html">balloon-borne telescope</a> that will circumnavigate the Antarctic continent, driven by the winds of the polar vortex. It will be followed by a telescope built by <a href="http://english.pmo.cas.cn/rh/dra/mcsf2/201109/t20110914_75047.html">China</a> on the very summit of the Antarctic plateau, at the new <a href="http://www.nature.com/news/china-aims-high-from-the-bottom-of-the-world-1.11291">Kunlun Observatory</a> at <a href="http://mcba11.phys.unsw.edu.au/%7Eplato/">Dome A</a>. </p>
<p>Bit by bit, we’re building the telescopes necessary to help shed light on carbon in space, and thus illuminate the grand carbon cycle that influences the evolution of the galaxy around us.</p><img src="https://counter.theconversation.com/content/48384/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Burton works for the University of New South Wales. He receives funding UNSW, the Australian Research Council and the Australian Antarctic Division. He is the President of Team Mopra Inc. He is on the Council of the Royal Society of New South Wales and the Editor of the Journal and Proceedings of the RSNSW.</span></em></p>Astronomers have built a new observatory in the cold dry air of a high plateau in Antarctica to peer through our atmosphere and observe carbon in our galaxy.Michael Burton, Professor in Physics and Astronomy, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/469882015-09-14T20:16:51Z2015-09-14T20:16:51ZWe are lucky to live in a universe made for us<figure><img src="https://images.theconversation.com/files/94602/original/image-20150914-1210-1et5w5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Like a cosmic roulette wheel, we exist because of a very lucky combination of factors.</span> <span class="attribution"><span class="source">NASA/JPL-Caltech</span></span></figcaption></figure><p>To a human, the universe might seem like a very inhospitable place. In the vacuum of space, you would rapidly suffocate, while on the surface of a star you would be burnt to a crisp. As far as we know, all life is confined to a sliver of an atmosphere surrounding the rocky planet we inhabit.</p>
<p>But while the origin of life on Earth remains mysterious, there are bigger questions to answer. Namely: why do the laws of physics permit any life at all? </p>
<p>Hang on, <em>the laws of physics</em>? Surely they are a universal given and life just gets on with it? </p>
<p>But remember that the universe is built of fundamental pieces, particles and forces, which are the building blocks of everything we see around us. And we simply don’t know why these pieces have the properties they do. </p>
<p>There are many observational facts about our universe, such as electrons weighing almost nothing, while some of their quark cousins are thousands of times more massive. And gravity being incredibly weak compared to the immense forces that hold atomic nuclei together. </p>
<p>Why is our universe built this way? We just don’t know.</p>
<h2>But what if…?</h2>
<p>This means we can ask “what if” questions. What if the electron was massive and quarks were fleeting? What if electromagnetism was stronger than the nuclear strong force? If so, what would that universe be like?</p>
<p>Let’s consider <a href="http://www.rsc.org/periodic-table/element/6/carbon">carbon</a>, an element forged in the hearts of massive stars, and an element essential to life as we know it.</p>
<p>Initial calculations of such stellar furnaces showed that they were apparently inefficient in making carbon. Then the British astronomer <a href="http://www.scientificamerican.com/article/hoyle-state-primordial-nucleus-behind-elements-life/">Fred Hoyle realised</a> the carbon nucleus possesses a special property, a resonance, that enhanced the efficiency.</p>
<p>But if the strength of the <a href="http://www.livescience.com/48575-strong-force.html">strong nuclear force</a> was only fractionally different, it would wipe out this property and leave the universe relatively devoid of carbon – and, thus, life. </p>
<p>The story doesn’t end there. Once carbon is made, it is ripe to be transmuted into heavier elements, particularly <a href="http://www.rsc.org/periodic-table/element/8/oxygen">oxygen</a>. It turns out that oxygen, due to the strength of the strong nuclear force, lacks the particular resonance properties that enhanced the efficiency of carbon creation.</p>
<p>This prevents all of the carbon being quickly consumed. The specific strength of the strong force has thus resulted in a universe with an almost equal mix of carbon and oxygen, a bonus for life on Earth. </p>
<h2>Death of a universe</h2>
<p>This is but a single example. We can play “what if” games with the properties of all of the fundamental bits of the universe. With each change we can ask, “What would the universe be like?”</p>
<p>The answers are quite stark. Straying just a little from the convivial conditions that we experience in our universe typically leads to a sterile cosmos. </p>
<p>This might be a bland universe, without the complexity required to store and process the information central to life. Or a universe that expands too quickly for matter to condense into stars, galaxies and planets. Or one that completely re-collapses again in a matter of moments after being born. Any complex life would be impossible!</p>
<p>The questions do not end there. In our universe, we live with the comfort of a certain mix of space and time, and a seemingly understandable mathematical framework that underpins science as we know it. Why is the universe so predictable and understandable? Would we be able to ask such a question if it wasn’t?</p>
<p>Our universe appears to balance on a knife-edge of stability. But why?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=386&fit=crop&dpr=1 600w, https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=386&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=386&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=485&fit=crop&dpr=1 754w, https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=485&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/94599/original/image-20150914-1212-875wb8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=485&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">We appear to be very lucky to live in a universe that accommodates life.</span>
<span class="attribution"><span class="source">Zdenko Zivkovic/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>One of a multiverse</h2>
<p>To some, science will simply fix it all. Perhaps, if we discover the “Theory of Everything”, uniting quantum mechanics with Einstein’s relativity, all of the relative masses and strengths of the fundamental pieces will be absolutely defined, with no mysteries remaining. To others, this is little more than wishful thinking.</p>
<p>Some seek solace in a creator, an omnipotent being that finely-tuned the properties of the universe to allow us to be here. But the move from the scientific into the supernatural leaves many uncomfortable.</p>
<p>There is, however, another possible solution, one guided by the murky and confused musings at the edge of science. Super-strings or M-theory (or whatever these will evolve into) suggest that the fundamental properties of the universe are not unique, but are somehow chosen by some cosmic roll of the dice when it was born. </p>
<p>This gives us a possible explanation of the seemingly special properties of the universe in which we live.</p>
<p>We are not the only universe, but just one in a semi-infinite sea of universes, each with their own peculiar set of physical properties, laws and particles, lifetimes and ultimately mathematical frameworks. As we have seen, the vast majority of these other universes in the overall multiverse are dead and sterile. </p>
<p>They only way we can exist to ask the question “why are we here?” is that we happen to find ourselves in a universe conducive to our very existence. In any other universe, we simply wouldn’t be around to wonder why we didn’t exist.</p>
<p>If the multiverse picture is correct, we have to accept that the fundamental properties of the universe were ultimately dished out in a game of cosmic roulette, a spin of the wheel that we appear to have won.</p>
<p>Thus we truly live in a fortunate universe.</p><img src="https://counter.theconversation.com/content/46988/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Geraint Lewis receives funding from the Australian Research Council.</span></em></p>If some of the laws of physics were only infinitesimally different, we would simply not exist. It almost looks like the universe itself was built for life. But how can that be?Geraint Lewis, Professor of Astrophysics, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/293412015-09-01T03:50:35Z2015-09-01T03:50:35ZExplainer: what is a neutron star?<figure><img src="https://images.theconversation.com/files/92871/original/image-20150825-17799-1waz2hg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">NASA artists' interpretation of the neutron star Swift J1749.4-2807 (left) with it's companion star (right).</span> <span class="attribution"><a class="source" href="http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=10625">NASA/Goddard Space Flight Center </a></span></figcaption></figure><p>Neutron stars are arguably the most exotic objects in the universe. Like one of those annoying friends who seemingly must overachieve in every aspect of life, neutron stars exceed in almost every category: surface gravity; magnetic field strength; density; and temperature.</p>
<p>“But wait,” I hear you say, “black holes are much denser!” In one sense that’s true, but we can’t actually determine the interior structure of a black hole, as it’s forever hidden behind the <a href="http://astronomy.swin.edu.au/cosmos/E/Event+Horizon">event horizon</a>.</p>
<p>Neutron stars, with a solid crust (and even oceans and an atmosphere!) are the densest solid object we can observe, reaching a few times the density of an atomic nucleus at their core. A sample of neutron star material the size of a grain of sand would weigh roughly the same as the <a href="http://www.largestships.com/seawise-giant/">largest ship</a> ever to sail the seas – more than 500,000 tonnes.</p>
<p>Neutron stars also offer a wealth of extreme behaviour which makes them a compelling target for astrophysicists. For the public, however, they seem to suffer from an image problem, lacking the visual appeal of objects that we can image directly, or the otherworldly weirdness of black holes.</p>
<h2>Origin of a neutron star</h2>
<p>Neutron stars are thought to be formed from the supernova explosion that ends the life of a medium-sized star, roughly eight to 20 times the mass of our sun. Once its nuclear fuel is consumed, the star explodes, losing most of its material into space.</p>
<p>What’s left collapses into a tiny object (by astronomical standards) around 22km across, the size of a large city, but still about one-and-a-half times the mass of our sun. </p>
<p>While the crust is composed mainly of crystalline iron, such atoms cannot survive deeper in the star, and the material transitions via a bizarre “nuclear pasta” phase (region A in the image, below) into the neutron fluid of the core (regions B and C).</p>
<p>The conditions in the core cannot be reproduced in any terrestrial experiments, and the uncertainty about this region – perhaps comprising exotic hyperons or even “strange quark matter” – is a prime motivator for studying these objects.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/92972/original/image-20150826-3245-klhvpa.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/92972/original/image-20150826-3245-klhvpa.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/92972/original/image-20150826-3245-klhvpa.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=675&fit=crop&dpr=1 600w, https://images.theconversation.com/files/92972/original/image-20150826-3245-klhvpa.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=675&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/92972/original/image-20150826-3245-klhvpa.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=675&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/92972/original/image-20150826-3245-klhvpa.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=848&fit=crop&dpr=1 754w, https://images.theconversation.com/files/92972/original/image-20150826-3245-klhvpa.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=848&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/92972/original/image-20150826-3245-klhvpa.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=848&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Anatomy of a neutron star.</span>
<span class="attribution"><a class="source" href="http://www.astroscu.unam.mx/neutrones/NS-Picture/NStar/NStar.html">Dany P Page</a></span>
</figcaption>
</figure>
<p>Neutron stars give off little visible light, making them practically impossible to detect in blind searches. Most of the few-thousand known examples have been discovered instead via their radio pulsations.</p>
<p>Like cosmic lighthouses, the paired radio beams from these pulsars sweep out across the universe. If the beam crosses the Earth, they may be detected with ground-based radio telescopes such as <a href="http://www.parkes.atnf.csiro.au">the Dish</a> at Parkes, New South Wales. The nearest pulsar, <a href="http://www.atnf.csiro.au/people/Simon.Johnston/papers/0437.html">PSR J0437-4715</a> is about 500 light-years away.</p>
<p>Of course, there are many more examples with beams that don’t reach the Earth, so the observed sample is a small fraction of the total galactic population. As well as these ordinary radio pulsars, there are several other more interesting flavours, also with rather quirky names:</p>
<ul>
<li>Rotating RAdio Transients (<a href="http://astronomy.swin.edu.au/cosmos/R/RRATs">RRATs</a>) are pulsars with (apparently!) wonky beams that flicker on and off</li>
<li><a href="http://astronomy.swin.edu.au/cosmos/M/Magnetar">magnetars</a> are pulsars with incredibly strong magnetic fields</li>
<li>microquasars are pulsars with <a href="http://www.astronomy.com/news/2015/08/neutron-stars-strike-back-at-black-holes-in-jet-contest">jets reaching relativistic speeds</a></li>
</ul>
<h2>All in a spin</h2>
<p>Typical pulsating neutron stars spin about once per second, which is remarkably fast for such a massive, dense object. But if the star happens to have a normal binary companion (see top image) the neutron star can “spin up” to more than ten times the speed of a typical washing machine on the spin cycle.</p>
<p>The process by which this occurs is called accretion. Over the thousand-million year lifetimes of these objects, the companion star evolves (and expands) until the outer layers feel the gravitational pull of the neutron star.</p>
<p>Gas from the companion star can then flow onto the neutron star, spinning it up, the same way that you can spin a free bicycle wheel with the stream from a garden hose.</p>
<p>This process has some remarkable side effects. The gas falling onto the neutron star is heated to tens of millions of degrees, and the neutron star will begin to shine brightly, in X-rays rather than radio waves. Such radiation is blocked by the Earth’s atmosphere, but can be detected by <a href="http://www.nasa.gov/press-release/nasa-selects-proposals-to-study-neutron-stars-black-holes-and-more">satellite-based telescopes</a> like those operated by NASA and the European Space Agency (ESA).</p>
<p>In fact, the brightest object in the X-ray sky, apart from the sun, is a likely neutron star, <a href="http://chandra.harvard.edu/xray_sources/sco/sco.html">Scorpius X-1</a> (the first X-ray source discovered in the constellation of Scorpius), which orbits it’s mass donor companion once every 19 hours.</p>
<h2>Fusion occurs</h2>
<p>The gas which collects on the surface of the neutron star via the accretion process is likely similar to the composition of our own sun – primarily hydrogen and helium, with a few per cent of other elements.</p>
<p>The neutron star’s enormous gravity – a few hundred billion times stronger than Earth’s – will compress and heat the gas, leading after a few hours or days to the point at which nuclear fusion can occur.</p>
<p>But this burning isn’t as well-behaved as in stars like the sun. Instead, the burning is unstable, and proceeds in just a few seconds to completely engulf the neutron star’s surface, exhausting all the accumulated fuel and giving rise to an X-ray burst visible across the galaxy.</p>
<p>These bursts have been observed in about 100 systems since the first X-ray telescopes were launched in the 1960s. Occurring once every few hours to days (depending upon the accretion rate), they are by far the most frequent thermonuclear explosions in the universe.</p>
<p>Of course, the supply of gas from the companion will eventually run out. And when that occurs, the neutron star may reprise it’s role as a radio pulsar, although now spinning hundreds of times every second. The current record-holder <a href="https://www.nrao.edu/pr/2006/mspulsar">PSR J1748-2446ad</a> spins 716 times every second!</p>
<p>But even neutron stars cannot remain active forever. Ultimately the spin energy will dissipate and without a companion to recycle it, the pulsar will cross the death line beyond which it is no longer detectable.</p>
<p>After that, the neutron star will gradually cool until the end of time. Until then, neutron stars will continue to serve as extraordinary laboratories for the study of matter under extreme densities and temperatures.</p><img src="https://counter.theconversation.com/content/29341/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Duncan Galloway has received funding from the Australian Research Council, and is the vice-president of the Astronomical Society of Australia.</span></em></p>They’re are the overachievers of the universe: incredibly dense but very small when compared to others stars. So how much do we know about the extreme behaviour of neutron stars?Duncan Galloway, PhD; Senior Lecturer in Astrophysics, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/457792015-08-10T20:11:13Z2015-08-10T20:11:13ZDon’t panic, but the universe is slowly dying<figure><img src="https://images.theconversation.com/files/91256/original/image-20150810-12450-5106w.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A colour image of G63349, one of the galaxies in the survey, created using near-infrared (VISTA telescope) and optical (Sloan telescope) data collated by the GAMA survey. (The bright green object is a nearby star.) </span> <span class="attribution"><span class="source">ICRAR/GAMA</span>, <span class="license">Author provided</span></span></figcaption></figure><p>We know that our universe has already lived through great number of exciting phases. But new <a href="http://www.icrar.org/news/news_items/media-releases/the-universe-is-dying2">research released overnight</a> shows the universe has long passed its peak and is slowly but surely dying.</p>
<p>The research was presented at the year’s largest gathering of astronomers at the <a href="http://www.iau.org/">International Astronomical Union</a>’s <a href="http://astronomy2015.org/">General Assembly in Hawaii</a>. But before we start writing any obituaries, let’s have a quick recap of the good times.</p>
<p>When the universe was less than a second old and more than a billion degrees Celsius, it was hot enough for exotic particles to freely pop in and out of existence. As the universe expanded, it cooled and was no longer able to produce hugely energetic particles.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/91133/original/image-20150807-27593-1n4hhws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/91133/original/image-20150807-27593-1n4hhws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/91133/original/image-20150807-27593-1n4hhws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=432&fit=crop&dpr=1 600w, https://images.theconversation.com/files/91133/original/image-20150807-27593-1n4hhws.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=432&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/91133/original/image-20150807-27593-1n4hhws.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=432&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/91133/original/image-20150807-27593-1n4hhws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=543&fit=crop&dpr=1 754w, https://images.theconversation.com/files/91133/original/image-20150807-27593-1n4hhws.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=543&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/91133/original/image-20150807-27593-1n4hhws.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=543&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A representation of the evolution of the universe over 13.77 billion years.</span>
<span class="attribution"><a class="source" href="http://map.gsfc.nasa.gov/media/060915/index.html">NASA / WMAP Science Team</a></span>
</figcaption>
</figure>
<p>After a few seconds, the universe was a sea of protons and neutrons, and after a few minutes it was mostly a dense fog of hydrogen and helium. In terms of building more complex matter, that was pretty much the end of the action for 400,000 years.</p>
<p>Then, quite suddenly, matter and radiation were decoupled and photons of light were able to free-stream across the universe for the first time. This is all very exciting for cosmology, but something important had also happened to the hydrogen and helium: it could now hold onto electrons and create neutral atoms.</p>
<h2>Early building blocks of life</h2>
<p>This is another step on the path to making you and me: we need neutral hydrogen in order to form molecular hydrogen, we need this to efficiently cool pockets of gas that collapse rapidly to form the first stars, and we need stars to form the heavy elements such as carbon and oxygen that are the building blocks of life.</p>
<p>By this stage the universe was a few hundred million years old, and it was now busy heating itself back up as these first stars irradiated the surrounding material.</p>
<p>These stars were blowing themselves apart and dumping large quantities of heavy atomic species into space, producing many of the heavier elements we see today. Some of them may also have collapsed into black holes, sowing the seeds of some of the most massive galaxies that exist in the present day universe.</p>
<p>After this early phase of forming the first stars, we began to see the first structures that resemble modern galaxies, but in a very messy and violent form. For the next few billion years galaxies smashed together to form more massive systems and star formation was rapidly turned on and off.</p>
<p>This activity continued until the universe was about 3 billion years old, a period we know as the peak of cosmic star formation. So the universe got most of the exciting stuff out of the way really early on.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/91144/original/image-20150807-27568-hsvjcg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/91144/original/image-20150807-27568-hsvjcg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/91144/original/image-20150807-27568-hsvjcg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/91144/original/image-20150807-27568-hsvjcg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/91144/original/image-20150807-27568-hsvjcg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/91144/original/image-20150807-27568-hsvjcg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/91144/original/image-20150807-27568-hsvjcg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/91144/original/image-20150807-27568-hsvjcg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A top down view of the major 3D redshift surveys of the local universe with the Earth at the centre. Each dot represents a single galaxy, and the direction shows their location on the sky. The distance from the centre shows the light travel time from Earth. Here we see the most recent 5 billion years of the universe, which has taken thousands of nights of observing on some of the most massive telescopes to construct.</span>
<span class="attribution"><span class="source">ICRAR/GAMA</span></span>
</figcaption>
</figure>
<p>What has it been doing since then? It is slowly but steadily dying. It is still producing new stars every now and again, but the rate at which old stars are fading outstrips these bright young things.</p>
<h2>Enter the dark stuff</h2>
<p>To exacerbate things even further, about 3 billion years ago a mysterious (and much studied) entity called <a href="https://theconversation.com/au/topics/dark-energy">dark energy</a> began to dominate the energy contents of the universe and accelerate everything apart (measuring this acceleration won Australian researcher <a href="https://theconversation.com/profiles/brian-schmidt-4963">Brian Schmidt</a> and others a <a href="https://theconversation.com/australian-astrophysicist-wins-nobel-prize-3707">Nobel prize</a>).</p>
<p>The universe had already started cooling off by this stage, so dark energy arriving on the scene really twisted the knife.</p>
<p>How do we know all of this? Well, we have been building the evidence for a while and careful models of galaxy evolution have already suggested that the <a href="http://www.theguardian.com/science/2003/aug/18/universe.sciencenews">universe is fading</a>, but we wanted to directly observe this effect over many billions of years.</p>
<p>In the past few years a large Australian led project called the Galaxy And Mass Assembly (<a href="http://www.gama-survey.org/">GAMA</a>) survey invested huge effort into measuring most of the energy output from stars.</p>
<p>We had to observe nearby galaxies from the far-ultraviolet (where young stars produce much of their light) through the optical and the near-infrared (where most stars peak in energy output) all the way into the far-infrared (where star light absorbed by dust is re-emitted).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/91137/original/image-20150807-27568-1nz7s36.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/91137/original/image-20150807-27568-1nz7s36.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/91137/original/image-20150807-27568-1nz7s36.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/91137/original/image-20150807-27568-1nz7s36.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/91137/original/image-20150807-27568-1nz7s36.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/91137/original/image-20150807-27568-1nz7s36.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/91137/original/image-20150807-27568-1nz7s36.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/91137/original/image-20150807-27568-1nz7s36.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A galaxy from the GAMA survey observed at different wavelengths from the far ultraviolet to the far infrared. The inset graph shows how much energy is being generated at different wavelengths.</span>
<span class="attribution"><span class="source">ICRAR/GAMA</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>GAMA has been able to measure this huge span of radiation over the past 5 billion years for almost 200,000 galaxies, categorically establishing that the energy output of stars in the universe is winding down.</p>
<h2>The end of the universe?</h2>
<p>The good news is that the stars made to date will still last many billions of years yet (including our own sun). Some of the smaller stars should keep shining for longer than the current age of the universe.</p>
<p>There are questions over what exactly the dominance of dark energy will mean in the long term, with some of more exotic theories speculating that it could tear everything apart in a “<a href="http://www.theguardian.com/science/2015/jul/02/not-with-a-bang-but-with-a-big-rip-how-the-world-will-end">Big Rip</a>”.</p>
<figure>
<iframe src="https://player.vimeo.com/video/88412829" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">Fly through of the GAMA Galaxy Survey.</span></figcaption>
</figure>
<p>Less dramatic, and more likely given our current knowledge, is the theory that the universe will continue to cool forever, and non gravitationally bound structures will steadily move apart from each other. After trillions of years we will only be able to see our own galaxy as the others will have raced too far away. After hundreds of trillions of years no new stars will be made anywhere at all.</p>
<p>Next our galaxy will eject most of its remaining stars into the cosmic void, and what is left will collapse into our central black hole. All matter as we know it will eventually decay, the black holes will evaporate and what is left will be a very lonely and empty place.</p>
<p>The universe will have ceased converting mass into light, and it will be left in almost total darkness. Every once in a while the remaining photons, electrons, positrons and neutrinos will meet and dance, but they will soon continue their solitary journeys. The universe, in any sense that we know it today, will be over.</p>
<p>The phase we are in now could be considered to be the slow death throes of the universe. But on a more upbeat note, this is its Indian summer. After those hectic early days I think we can all agree that it deserves a good rest.</p><img src="https://counter.theconversation.com/content/45779/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Aaron Robotham works at ICRAR UWA, a major centre for work using GAMA data. He receives funding from the ARC for research related to GAMA.</span></em></p>Our universe’s most exciting days are well behind us, with new research showing the universe is now slowly but surely dying.Aaron Robotham, Research Associate Professor & UWA Research Fellow, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/448622015-07-20T13:20:55Z2015-07-20T13:20:55ZWhy is life left-handed? The answer is in the stars<figure><img src="https://images.theconversation.com/files/88972/original/image-20150720-12527-zsov20.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A needle in a haystack? Search for the first ever biological molecule.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/hubble-heritage/3195127686/in/photolist-bzHLe1-pRmoBZ-8cNsDh-5SkS9o-vdGXRR-qGTuRP-cAtpZw-mcn7tg-krBMuv-gfvMZg-7oqYzo-8ifuyk-cPfnQ5-7VGxyE-hyzMyT-r6hhL6-5SDGMX-8pHHKM-9a2kmG-5Zv7DK-6Z68Po-9a2i63-dWfLLA-8ifUyx-99Yay2-5ScPu6-5Snpeb-5SGJQF-5SnpeY-5S3FxJ-bjDabU-5Snp8W-efWFpq-42J3BP-d4VvWq-nteJ2t-r3yXtG-v1FVCo-5S4DAu-uoeg85-hEWtfw-fTVzqs-f3g2Tk-eRuG22-j7RzoQ-m5ojsM-m5nSqr-fbwjeP-cZdTA5-cA7y8W">Hubble Heritage/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>While most humans are right-handed, our proteins are made up of lefty molecules. In the same way your left and right hands mirror one another, molecules can assemble in two reflected structures. Life prefers the left-handed version, which is puzzling since both mirrored types form equally in the laboratory. But a new study suggests that this may be because the star-forming cloud that created the <a href="http://www.sciencedirect.com/science/article/pii/S0009261415004133">first-ever biological molecule</a>, before our sun was even born, made it left-handed.</p>
<p>In 2004, NASA’s Stardust spacecraft <a href="http://stardust.jpl.nasa.gov/news/news116.html">swept through the nebulous halo surrounding a comet</a>. What it found was the simplest of life’s building blocks: the <a href="http://www.biology.arizona.edu/biochemistry/problem_sets/aa/glycine.html">amino acid glycine</a>. Comets are <a href="http://solarsystem.nasa.gov/planets/profile.cfm?Object=Comets">frozen remnants</a> from the earliest days in our solar system. Their material is therefore not made in planets, but likely originates in the natal gas cloud that formed our sun.</p>
<p>A <a href="http://www.lowtem.hokudai.ac.jp/astro/index_e.html">research team</a> recently recreated the freezing conditions inside such a star-forming cloud. In apparatus sealed completely from the already crisp air in the laboratory, the temperature can be brought down to -263 degrees Celsius, just ten degrees above absolute zero where even molecules stop vibrating. They believed that on the surface of dust grains suspended in this chilly gas, glycine may have undergone a change that made it left-handed. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/88848/original/image-20150717-21031-1rntkfz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88848/original/image-20150717-21031-1rntkfz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=407&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88848/original/image-20150717-21031-1rntkfz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=407&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88848/original/image-20150717-21031-1rntkfz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=407&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88848/original/image-20150717-21031-1rntkfz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=512&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88848/original/image-20150717-21031-1rntkfz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=512&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88848/original/image-20150717-21031-1rntkfz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=512&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Protein molecules: just a bunch of lefties.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Chirality_%28chemistry%29#/media/File:Chirality_with_hands.svg">Perhelion/wikimedia</a></span>
</figcaption>
</figure>
<p>At the core of the glycine molecule is a carbon atom with four bonds. If two of these bonds attach to hydrogen atoms, then the molecule is symmetric and neither right nor left handed. However, swap a hydrogen for a heavier atom and this symmetry is broken. The molecule can then form two mirrored versions, giving it handedness or “<a href="http://www.chirality.org/homepage.htm">chirality</a>” as it is called in chemistry. </p>
<p>The experiments suggest that a glycine hydrogen atom could be displaced by an atom of deuterium, which is a heavier version of hydrogen that contains an extra neutron in its nucleus, doubling its weight. It is abundant inside star-forming clouds, which is why they create <a href="http://www.astrobio.net/news-exclusive/cosmic-chemistry-gave-rise-water/">many deuterium-enriched compounds</a>, including heavy water. Once a deuterium atom has replaced a hydrogen, it is very hard to dislodge. This means that the fraction of chiral glycine steadily increases, until the main species of glycine inside the cloud shows left or right handedness.</p>
<p>Chiral glycine is very similar to original glycine, but with an important extra property. Laboratory experiments have shown that chiral glycine <a href="http://www.rsc.org/Publishing/ChemScience/Volume/2009/08/achiral_key.asp">is a catalyst for other chiral molecules</a>. That is, it promotes the production of other species with the same handedness as itself. </p>
<p>The result is that if glycine became a left-handed molecule, then future biological molecules would also be predominantly left-handed. When life developed on Earth, it would therefore build from a pool of left-handed molecules, giving it the bias we observe today.</p>
<h2>Pinning down glycine in space</h2>
<p>This discovery potentially resolves another issue. While glycine is expected to be abundant inside star-forming clouds, it has never actually been observed. Individual molecules absorb different wavelengths of the starlight passing through them. Which wavelengths are absorbed depends on the atoms and their arrangement, providing a fingerprint for the presence of a particular molecule. Glycine’s fingerprint has never been seen. However, these searches have been looking for the symmetric version of glycine, not its left-handed twin. If most of the glycine was left-handed, it would absorb different wavelengths and be missed. </p>
<p>It is an exciting idea, but many questions still remain. In the new experiment, the scientists could tell that deuterium had replaced hydrogen to form chiral glycine, but the quantities were too small to see which mirrored version had formed. </p>
<p>It could be that the dust grain structure favours left or right handedness. Alternatively, both types could form but one might be more easily destroyed. The answer to this would tell us if life beyond our own solar system is expected to share our left-handed bias.</p><img src="https://counter.theconversation.com/content/44862/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Elizabeth Tasker is a faculty member at Hokkaido University. </span></em></p>Researchers have created a star-forming cloud in the laboratory to try to recreate the first-ever biological molecule. The study could explain why such molecules are left-handed.Elizabeth Tasker, Assistant Professor, Hokkaido UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/403102015-04-17T02:37:10Z2015-04-17T02:37:10ZGiant galaxies die from the inside when they stop making stars<figure><img src="https://images.theconversation.com/files/78225/original/image-20150416-5654-8vvagi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Elliptical galaxies, like this one, are burnt out and no longer making stars.</span> <span class="attribution"><a class="source" href="http://www.eso.org/public/australia/images/eso1516b/">Judy Schmidt and J Blakeslee (Dominion Astrophysical Observatory)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Galaxies are star factories. But for some, such as massive <a href="http://astronomy.swin.edu.au/cosmos/E/Elliptical+Galaxy">elliptical galaxies</a>, their star-forming days are now over. All of their available gas has already been turned into more than a hundred billion stars. </p>
<p>Collectively, these galaxies contain about half of all the stars that have ever existed in the universe.</p>
<p>In a new study, published in <a href="http://www.sciencemag.org/content/348/6232/314.abstract?sid=98160635-c374-4238-9d6b-e48d01924083">Science</a>, astronomers have tracked down how the fire of star formation burnt out within these galaxies.</p>
<p>It appears that most of the time, the star formation is first quenched within the heart of the galaxy, and it’s not until a few billion years later that the outer regions run out of gas and stop producing stars.</p>
<p>This discovery that giant galaxies die from the inside-out is useful for astronomers trying to understand the mechanisms that promote and hinder star formation. And, ultimately, it’s about unravelling the history of the universe and understanding why we see the kinds of galaxies that exist today. </p>
<h2>Our universe, the time machine</h2>
<p>It’s one of the mind-boggling things about astronomy that every time we look into space, we are looking back in time. The universe is so vast, that even though light hurtles across space at 300,000 km/s, its journey can last billions of years. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78224/original/image-20150416-30509-vy7t4l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78224/original/image-20150416-30509-vy7t4l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78224/original/image-20150416-30509-vy7t4l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78224/original/image-20150416-30509-vy7t4l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78224/original/image-20150416-30509-vy7t4l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78224/original/image-20150416-30509-vy7t4l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78224/original/image-20150416-30509-vy7t4l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78224/original/image-20150416-30509-vy7t4l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">At 65 million light years away, the light of the Virgo Cluster began its journey around the same time that the dinosaurs became extinct.</span>
<span class="attribution"><span class="source">NASA, ESA</span></span>
</figcaption>
</figure>
<p>The light emitted from the 22 galaxies investigated in this study has taken more than 10 billion years to reach us. We are seeing these galaxies from a time when the universe was around three billion years old. </p>
<p>It was the heyday of the universe, when galaxies were vigorously forming stars at a rate about 20 times faster than occurs today. Each year, massive galaxies were producing the equivalent of hundreds of sun-like stars. In comparison, our Milky Way Galaxy creates just four sun-like stars a year. </p>
<p>And when the universe was young, it was the most massive galaxies that were undergoing <a href="http://arxiv.org/abs/1306.2424">the fastest growth</a>, as confirmed by the Galaxy and Mass Assembly (<a href="http://www.gama-survey.org/">GAMA</a>) project, a major study being undertaken in Australia with the <a href="http://www.aao.gov.au/">Anglo-Australian Telescope</a>.</p>
<p>So how does the growth slow down? </p>
<h2>Steady as she goes</h2>
<p>To answer this, PhD student <a href="http://www.astro.ethz.ch/carollo/the-group/people/person-details.html?persid=144978">Sandro Tacchella</a> (<a href="https://www.ethz.ch/en.html">ETH Zurich</a>, Switzerland) and colleagues used observations from both the Hubble Space Telescope (<a href="http://hubblesite.org/">HST</a>) and the European Southern Observatory’s Very Large Telescope (<a href="http://www.eso.org/public/teles-instr/vlt/">VLT</a>). Images from the HST, were used to trace the distribution of older stars within the galaxies – the locations where star formation had previously occurred. </p>
<p>Using an instrument known as <a href="http://www.eso.org/sci/facilities/paranal/instruments/sinfoni.html">SINFONI</a> on the VLT, the astronomers looked for regions where star formation was actively occurring. This is done by searching for hydrogen gas that has been excited or <a href="http://astronomy.swin.edu.au/cosmos/I/ionised+hydrogen">ionised</a> by the radiation emitted from young, hot stars.</p>
<p>To be useful, both sets of observations needed to track changes across small spatial scales. The HST can do this because it’s in space and doesn’t have to deal with the blurring effects of the Earth’s atmosphere. </p>
<p>It’s harder for the VLT to resolve small parts of the distant galaxies because the telescope sits on Earth’s surface, in Chile, and must cancel out Earth’s atmospheric effects. The VLT does this by monitoring an artificial star (<a href="https://theconversation.com/laser-helps-find-supermassive-black-hole-in-a-small-galaxy-31744">produced by a laser</a>), then keeps the starlight steady by <a href="https://www.eso.org/public/australia/teles-instr/technology/adaptive_optics/">deforming its mirrors</a>, making the results even more impressive. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78232/original/image-20150416-30509-1p72e4u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78232/original/image-20150416-30509-1p72e4u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78232/original/image-20150416-30509-1p72e4u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78232/original/image-20150416-30509-1p72e4u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78232/original/image-20150416-30509-1p72e4u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78232/original/image-20150416-30509-1p72e4u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78232/original/image-20150416-30509-1p72e4u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78232/original/image-20150416-30509-1p72e4u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The VLT uses an artificial star to track turbulence in the atmosphere.</span>
<span class="attribution"><span class="source">ESO/G Hüdepohl</span></span>
</figcaption>
</figure>
<h2>Red and dead</h2>
<p>Together, the observations showed that among the most massive galaxies of the sample, stars built-up quickly in the central regions of the galaxy but then stopped. While slow and steady star formation lingered in the galaxy’s outskirts.</p>
<p>A comparison was made with galaxies of similar mass that are much closer and therefore have been around for a far longer time since the <a href="http://astronomy.swin.edu.au/cosmos/B/Big+Bang">Big Bang</a>. </p>
<p>These are the “<a href="https://www.nasa.gov/mission_pages/chandra/news/red-and-dead-galaxies.html">red and dead</a>” galaxies, so called because they contain only red stars (which are cooler and more evolved, than young, hot blue stars) and the star formation has all dried up. A galaxy that is no longer forming stars is no longer growing, and therefore “dead”.</p>
<p>The central bulges of the massive galaxies – both the young (or distant) and the old (or nearby) – are very similar. These nearby galaxies are modern-day equivalents; they reveal to us that their central bulges were already in their current form 10 billion years ago. </p>
<h2>What can kill a galaxy?</h2>
<p>The key factor in understanding the shut-off of star formation in a galaxy is to know where its gas lives. Gas is the fuel from which new stars form, like the logs added to a campfire to keep it burning. Not only must the logs be present in order to burn, they have to be thrown on to the fire in order to ignite. </p>
<p>There are a number of mechanisms that could potentially strip gas from a galaxy or prevent the gas from getting onto the galaxy’s disk where is where it needs to be to create stars. Some of these processes are internal to the galaxy itself, while others depend on how crowded the neighbourhood is where the galaxy lives. </p>
<p>Many galaxies, especially ellipticals, are found in dense cities of galaxies called clusters. It has been suggested that within these dense environments <a href="http://www.swinburne.edu.au/chancellery/mediacentre/media-centre/news/2013/11/galaxies-in-groups-are-running-out-of-fuel">gas can be stripped away</a> from a galaxy via processes such as <a href="http://astronomy.swin.edu.au/cosmos/R/Ram+Pressure+Stripping">ram pressure stripping</a> and <a href="http://astronomy.swin.edu.au/cosmos/G/Galaxy+Strangulation">galaxy strangulation</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78234/original/image-20150416-5622-bgciy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78234/original/image-20150416-5622-bgciy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78234/original/image-20150416-5622-bgciy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=623&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78234/original/image-20150416-5622-bgciy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=623&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78234/original/image-20150416-5622-bgciy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=623&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78234/original/image-20150416-5622-bgciy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=783&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78234/original/image-20150416-5622-bgciy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=783&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78234/original/image-20150416-5622-bgciy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=783&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Galaxy clusters are impressive but do they hinder star formation?</span>
<span class="attribution"><span class="source">NASA, N Benitez (JHU), T Broadhurst (Racah Institute of Physics/The Hebrew University), H Ford (JHU), M Clampin (STScI), G Hartig (STScI), G Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA</span></span>
</figcaption>
</figure>
<p>But such processes remove gas from the outer regions of a galaxy and are at odds with Tacchella’s discovery, that star-forming gas survives the longest at a galaxy’s periphery. </p>
<p>A GAMA study of nearby galaxies with slightly less mass than our Milky Way Galaxy also showed <a href="http://arxiv.org/pdf/1308.2985v1.pdf">no evidence</a> that star formation is quenched by a galaxy’s local environment. The galaxies in that study continue to form stars at a rate of a few sun-like stars per year and could indicate that an environmental shut down of star formation is a very rapid process.</p>
<p>It’s not possible to rule out external factors completely – mechanisms that could stop the flow of gas into a galaxy and starve it of new fuel for stars. But with the kind of inside-out quenching that is observed, Tacchella and colleagues suggest that the process is likely internal to the galaxy. </p>
<h2>Bring in the black hole</h2>
<p>What’s going on in a galaxy’s core? A <a href="https://theconversation.com/scary-monsters-and-supermassive-black-holes-4661">big black hole</a>, that’s what. Astronomer’s call them supermassive, because they typically harbour as much mass as a few million or even a billion suns.</p>
<p>Black holes are known for their ability to draw material in, a result of their strong gravitational pull. But they also stir up powerful winds and jets that can push gas out of a galaxy. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78231/original/image-20150416-30509-1yb4e4n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78231/original/image-20150416-30509-1yb4e4n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78231/original/image-20150416-30509-1yb4e4n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=352&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78231/original/image-20150416-30509-1yb4e4n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=352&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78231/original/image-20150416-30509-1yb4e4n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=352&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78231/original/image-20150416-30509-1yb4e4n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=443&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78231/original/image-20150416-30509-1yb4e4n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=443&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78231/original/image-20150416-30509-1yb4e4n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=443&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An outflow from a supermassive black hole can suppress star formation within a galaxy.</span>
<span class="attribution"><span class="source">ESA/ATG medialab</span></span>
</figcaption>
</figure>
<p>Just last month, <a href="http://www.nature.com/nature/journal/v519/n7544/full/nature14261.html">Nature</a> published the first detection of a supermassive black hole <a href="http://www.esa.int/Our_Activities/Space_Science/Herschel/Black_hole_winds_pull_the_plug_on_star_formation">blasting out winds</a> that stripped the galaxy of its potential to form stars.</p>
<p>In addition, it is only within the most dense galaxy cores that star-formation is being quenched, which may suggest that once a critical density is reached, the galaxy stabilises, no longer lets fresh gas into its centre and <a href="http://arxiv.org/abs/1406.5372">self-quenches star formation</a>. </p>
<p>It’s an amazing thing to be able to observe a set of galaxies that are 10 billion light years away and dissect them to figure out what regions are still active, compared to other areas where galaxy growth has ended. This result provides new information on the lasting question of why and how massive galaxies stop forming new stars.</p><img src="https://counter.theconversation.com/content/40310/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tanya Hill is the Australian representative for the European Southern Observatory (ESO) Science Outreach Network.</span></em></p><p class="fine-print"><em><span>Amanda Bauer previously received funding from the Australian Research Council. She works for the Australian Astronomical Observatory.</span></em></p><p class="fine-print"><em><span>Sarah Brough receives funding from the Australian Research Council and the Australian Astronomical Observatory.</span></em></p>What happens to a galaxy when it runs out of the stuff needed to forge new stars?Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museums Victoria Research InstituteAmanda Bauer, PhD; Astronomer and Outreach Officer, Australian Astronomical ObservatorySarah Brough, Future Fellow, Australian Astronomical ObservatoryLicensed as Creative Commons – attribution, no derivatives.