tag:theconversation.com,2011:/nz/topics/galaxy-3110/articlesGalaxy – The Conversation2023-09-11T12:34:24Ztag:theconversation.com,2011:article/2113262023-09-11T12:34:24Z2023-09-11T12:34:24ZPowerful black holes might grow up in bustling galactic neighborhoods<figure><img src="https://images.theconversation.com/files/545840/original/file-20230831-17-di646s.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1280%2C1280&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A quasar is a galactic object with a supermassive black hole in the center. </span> <span class="attribution"><a class="source" href="https://noirlab.edu/public/images/noirlab2015a/">International Gemini Observatory/NOIRLab/NSF/AURA/P. Marenfeld</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span></figcaption></figure><p>As people, we are all shaped by the neighborhoods we grew up in, whether it was a bustling urban center or the quiet countryside. Objects in distant outer space are no different. </p>
<p>As an <a href="https://www.as.arizona.edu/people/postdoctoral/jaclyn-champagne">astronomer at the University of Arizona</a>, I like to think of myself as a cosmic historian, tracking how supermassive black holes grew up.</p>
<p>Like you, <a href="https://theconversation.com/say-hello-to-sagittarius-a-the-black-hole-at-the-center-of-the-milky-way-galaxy-183008">every supermassive black hole lives in a home</a> – its host galaxy – and a neighborhood – its local group of other galaxies. A supermassive black hole grows by consuming gas already inside its host galaxy, sometimes reaching a billion times heavier than our Sun. </p>
<p>Theoretical physics predicts that black holes should take billions of years to <a href="https://theconversation.com/new-powerful-telescopes-allow-direct-imaging-of-nascent-galaxies-12-billion-light-years-away-74910">grow into quasars</a>, which are extra bright and powerful objects powered by black holes. Yet astronomers know that many quasars have formed in <a href="https://www.eurekalert.org/news-releases/709408">only a few hundred million years</a>.</p>
<p>I’m fascinated by this peculiar problem of faster-than-expected black hole growth and am working to solve it by zooming out and examining the space around these black holes. Maybe the most massive quasars are city slickers, forming in hubs of tens or hundreds of other galaxies. Or maybe quasars can grow to huge proportions even in the most desolate regions of the universe.</p>
<h2>Galaxy protoclusters</h2>
<p>The largest object that can form in the universe is a galaxy cluster, containing hundreds of galaxies pulled by gravity to a common center. Before these grouped galaxies collapse into a single object, astronomers call them <a href="https://doi.org/10.1093/mnras/stv1449">protoclusters</a>. In these <a href="https://www.scientificamerican.com/article/ancient-galaxy-clusters-offer-clues-about-the-early-universe/">dense galaxy neighborhoods</a>, astronomers see colliding galaxies, growing black holes and great swarms of gas that will eventually become the next generation of stars. </p>
<p>These protocluster structures grow much faster than we thought, too, so we have a second cosmic problem to solve – how do quasars and protoclusters evolve so quickly? Are they connected? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/544797/original/file-20230825-19-i9q2fx.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Red clouds with a bright white center." src="https://images.theconversation.com/files/544797/original/file-20230825-19-i9q2fx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544797/original/file-20230825-19-i9q2fx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=339&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544797/original/file-20230825-19-i9q2fx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=339&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544797/original/file-20230825-19-i9q2fx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=339&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544797/original/file-20230825-19-i9q2fx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=426&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544797/original/file-20230825-19-i9q2fx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=426&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544797/original/file-20230825-19-i9q2fx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=426&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 simulation of a galaxy protocluster forming. In white, clouds of dark matter collapse and merge, while the red shows the motions of gas falling into the gravitational pull of the dark matter halos.</span>
<span class="attribution"><a class="source" href="https://www.tng-project.org/media/">TNG Collaboration</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<p>To look at protoclusters, astronomers ideally <a href="https://theconversation.com/looking-back-toward-cosmic-dawn-astronomers-confirm-the-faintest-galaxy-ever-seen-207602">obtain images</a>, which show the galaxy’s shape, size and color, and a spectrum, which shows the galaxy’s distance from Earth through specific wavelengths of light, for each galaxy in the protocluster. </p>
<p>With telescopes like the James Webb Space Telescope, astronomers can see galaxies and black holes <a href="https://theconversation.com/the-most-powerful-space-telescope-ever-built-will-look-back-in-time-to-the-dark-ages-of-the-universe-169603">as they were billions of years ago</a>, since the light emitted from distant objects must travel billions of light-years to reach its detectors. We can then look at protoclusters’ and quasars’ baby pictures to see how they evolved at early times.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/545633/original/file-20230830-17-gwpqna.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A graph with the y axis reading 'brightness' and the x reading 'wavelength.' A squiggly green line has peaks, with an arrow pointing to the reading 'hydrogen' and 'oxygen.'" src="https://images.theconversation.com/files/545633/original/file-20230830-17-gwpqna.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/545633/original/file-20230830-17-gwpqna.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/545633/original/file-20230830-17-gwpqna.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/545633/original/file-20230830-17-gwpqna.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/545633/original/file-20230830-17-gwpqna.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/545633/original/file-20230830-17-gwpqna.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/545633/original/file-20230830-17-gwpqna.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&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 example of a galaxy image and spectrum from the ASPIRE program at the University of Arizona. The inset shows the infrared image of a galaxy 800 million years after the Big Bang. The spectrum shows signatures of hydrogen and oxygen emission lines, whose wavelengths translate mathematically to a 3D location in space.</span>
<span class="attribution"><span class="source">J. Champagne/ASPIRE/University of Arizona</span></span>
</figcaption>
</figure>
<p>It is only after looking at spectra that astronomers determine whether the galaxies and quasars are actually close together in three-dimensional space. But getting spectra for every galaxy one at a time can take many more hours than any astronomer has, and images can show galaxies that look <a href="https://doi.org/10.3847/1538-4357/acda8d">closer together than they actually are</a>. </p>
<p>So, for a long time, it was only a prediction that massive quasars might be evolving at the centers of vast galactic cities. </p>
<h2>An unprecedented view of quasar environments</h2>
<p>Now, Webb has completely revolutionized the search for galaxy neighborhoods because of an instrument called a <a href="https://webb.nasa.gov/content/observatory/instruments/nircam.html">wide-field slitless spectrograph</a>. </p>
<p>This instrument takes spectra of every galaxy in its field of view simultaneously so astronomers can map out an entire cosmic city at once. It encodes the critical information about galaxies’ 3D locations by capturing the light emitted from gas at specific wavelengths – and in only a few hours of observing time.</p>
<p>The first Webb projects are hoping to look at quasar environments focused on a period about 800 million years after the Big Bang. This time period is a sweet spot in which astronomers can view these monster quasars and their neighbors using the light emitted by hydrogen and oxygen. The wavelengths of these light features show where the objects emitting them are along our line of sight, allowing astronomers to complete the census of where galaxies live relative to bright quasars.</p>
<p>One such ongoing project is led by <a href="https://aspire-quasar.github.io/">the ASPIRE team</a> at the University of Arizona’s Steward Observatory. In an <a href="https://webbtelescope.org/contents/news-releases/2023/news-2023-124?user=choquet">early paper</a>, they found a protocluster around an extremely bright quasar and confirmed it with 12 galaxies’ spectra. </p>
<p><a href="https://doi.org/10.3847/1538-4357/acc588">Another study</a> detected over a hundred galaxies, looking toward the single most luminous quasar known in the early universe. Twenty-four of those galaxies were close to the quasar or in its neighborhood.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/544641/original/file-20230824-23-4uejft.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Many bright dots representing galaxies, against a black backdrop." src="https://images.theconversation.com/files/544641/original/file-20230824-23-4uejft.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544641/original/file-20230824-23-4uejft.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=704&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544641/original/file-20230824-23-4uejft.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=704&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544641/original/file-20230824-23-4uejft.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=704&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544641/original/file-20230824-23-4uejft.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=885&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544641/original/file-20230824-23-4uejft.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=885&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544641/original/file-20230824-23-4uejft.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=885&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 neighborhood of galaxies around J0305-3150, a quasar identified approximately 800 million years after the Big Bang.</span>
<span class="attribution"><a class="source" href="https://webbtelescope.org/contents/news-releases/2023/news-2023-124">STScI/NASA</a></span>
</figcaption>
</figure>
<p>In ongoing work, my team is learning more details about mini galaxy cities like these. We want to figure out if individual galaxies show high rates of new star formation, if they contain large masses of old stars or if they are merging with one another. All these metrics would indicate that these galaxies are still actively evolving but had already formed millions of years before we observed them.</p>
<p>Once my team has a list of the properties of the galaxies in an area, we’ll compare these properties with a control sample of random galaxies in the universe, far away from any quasar. If these metrics are different enough from the control, we’ll have good evidence that quasars do grow up in special neighborhoods – ones developing much faster than the more sparse regions of the universe. </p>
<p>While astronomers still need more than a handful of quasars to prove this hypothesis on a larger scale, Webb has already opened a window into a bright future of discovery in glorious, high-resolution detail.</p><img src="https://counter.theconversation.com/content/211326/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jaclyn Champagne receives funding from the National Science Foundation and the Space Telescope Science Institute. The results from ASPIRE are supported by data and funding from JWST program GO-2078. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. </span></em></p>An astronomer and ‘black hole historian’ explains how the parts of the universe black holes grow in might influence how quickly they become bright, supermassive objects.Jaclyn Champagne, JASPER Postdoctoral Researcher, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1382052020-05-12T19:47:10Z2020-05-12T19:47:10ZExperts solve the mystery of a giant X-shaped galaxy, with a monster black hole as its engine<p>A team of US and South African researchers has <a href="https://arxiv.org/abs/2005.02723">published</a> highly detailed images of the largest X-shaped “radio galaxy” ever discovered – PKS 2014-55.</p>
<p>Notably, they’ve helped resolve ongoing confusion about the galaxy’s unusual shape.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/334265/original/file-20200512-175224-f1dbkn.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/334265/original/file-20200512-175224-f1dbkn.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/334265/original/file-20200512-175224-f1dbkn.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=732&fit=crop&dpr=1 600w, https://images.theconversation.com/files/334265/original/file-20200512-175224-f1dbkn.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=732&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/334265/original/file-20200512-175224-f1dbkn.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=732&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/334265/original/file-20200512-175224-f1dbkn.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=920&fit=crop&dpr=1 754w, https://images.theconversation.com/files/334265/original/file-20200512-175224-f1dbkn.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=920&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/334265/original/file-20200512-175224-f1dbkn.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=920&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 image of the giant X-shaped radio galaxy PKS 2014-55.</span>
<span class="attribution"><span class="source">Courtesy of SARAO and Bill Cotton et al/Author provided (no reuse)</span></span>
</figcaption>
</figure>
<p>The <a href="https://www.sarao.ac.za/media-releases/south-africas-meerkat-solves-mystery-of-x-galaxies/">spectacular new images</a> were taken using the 64-antenna <a href="https://www.sarao.ac.za/science-engineering/meerkat/about-meerkat/">MeerKAT</a> telescope in South Africa, by an international research team led by Bill Cotton of the US National Radio Astronomy Observatory. </p>
<h2>Zooming in on a cosmic giant</h2>
<p>Our research team also took detailed images of galaxy PKS 2014-55 last year, as part of the <a href="https://en.wikipedia.org/wiki/Evolutionary_Map_of_the_Universe">Evolutionary Map of the Universe project</a> led
by astrophysicist <a href="https://www.atnf.csiro.au/people/Ray.Norris/">Ray Norris</a>. We used CSIRO’s <a href="https://www.csiro.au/en/Research/Astronomy/ASKAP-and-the-Square-Kilometre-Array/SKA">Australian Square Kilometre Array Pathfinder</a> (ASKAP) telescope in Western Australia, which just completed its first set of pilot astronomical surveys. </p>
<p>Thanks to its innovative “radio cameras”, ASKAP can rapidly map very large areas of the sky to catalogue millions of objects emitting radio waves, from nearby supernova remnants to distant galaxies.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/334287/original/file-20200512-175219-s8xxo0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/334287/original/file-20200512-175219-s8xxo0.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=782&fit=crop&dpr=1 600w, https://images.theconversation.com/files/334287/original/file-20200512-175219-s8xxo0.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=782&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/334287/original/file-20200512-175219-s8xxo0.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=782&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/334287/original/file-20200512-175219-s8xxo0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=983&fit=crop&dpr=1 754w, https://images.theconversation.com/files/334287/original/file-20200512-175219-s8xxo0.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=983&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/334287/original/file-20200512-175219-s8xxo0.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=983&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Our ASKAP image of the giant X-shaped radio galaxy PKS 2014-55.</span>
<span class="attribution"><span class="source">CSIRO and the EMU team/Author provided (no reuse).</span></span>
</figcaption>
</figure>
<p>The prominent X-shape of PKS 2014-55 is made up of two pairs of <a href="https://blog.galaxyzoo.org/2014/02/03/the-curious-lives-of-radio-galaxies-part-one/">giant lobes</a> consisting of hot jets of electrons. These jets spurt outwards from a <a href="https://astronomy.swin.edu.au/cosmos/S/Supermassive+Black+Hole">supermassive black hole</a> at the galaxy’s heart.</p>
<p>The lobes emit electromagnetic radiation in the form of radio waves, which can only be detected by radio telescopes like <a href="https://www.csiro.au/en/Research/Facilities/ATNF/ASKAP">ASKAP</a>. Humans can’t see radio waves. But if we could, from Earth PKS 2014-55 would look about the same size as the Moon.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-the-universe-looks-like-when-viewed-with-radio-eyes-66381">What the universe looks like when viewed with radio eyes</a>
</strong>
</em>
</p>
<hr>
<h2>What makes a radio galaxy?</h2>
<p>Typically, <a href="https://en.wikipedia.org/wiki/Radio_galaxy">radio galaxies</a> have only one pair of lobes. One is a “jet” and the other a “counter-jet”. </p>
<p>These jets expand into the surrounding space at nearly the speed of light. They initially move in a straight line, but twist and bend into many marvellous shapes as they encounter their surroundings. </p>
<p>Centaurus A, seen below, is an example of a giant elliptical galaxy with two prominent radio lobes. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/334245/original/file-20200512-66657-3w0228.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/334245/original/file-20200512-66657-3w0228.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/334245/original/file-20200512-66657-3w0228.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/334245/original/file-20200512-66657-3w0228.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/334245/original/file-20200512-66657-3w0228.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/334245/original/file-20200512-66657-3w0228.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/334245/original/file-20200512-66657-3w0228.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/334245/original/file-20200512-66657-3w0228.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">This is an artist’s impression of the famous Centaurus A galaxy, which has two prominent radio lobes emerging from its central black hole.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/gsfc/18199018792/in/photolist-tJbJf5-2dNEVuC-29htjhd-EEHmKy-rzqGTD-95Yds7-VWRqoY-9KgqiH-qLsNuo-2hREZpf-2i9UMm7-U7eWMd-2h9dNaZ-2hcZa9a-2gGzwWB-2g2YXPm-26Twqde-2iyBv3a-D2Jexx-2dYDFz5-HbrkoD-2iKYoeb-2ecFGiW-S9bNa5-2hn6G22-2i2DXQD-2icZgrT-2f7Tk25-YW3jMi-dyhNrD-tv7Viw-2ioaJLK-2cPDMFH-2iw39Y4-Nf1txG-wTUY9C-2hmvcEb-25jHWii-2hSYj8B-dxh7au-2iRWf2C-2iw2z2v-YW3DJX-PNyWWK-fue4yp-6JLH7w-2hUxAFv-7Hb1Zt-6Zfmp7-9KgqhX">NASA Goddard Space Flight Center/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Galaxy PKS 2014-55’s <a href="https://blog.galaxyzoo.org/2014/02/04/the-curious-lives-of-radio-galaxies-part-two/">giant X-shape</a>, with two pairs of lobes emerging at very different angles, is highly unusual. </p>
<h2>What makes the lobes?</h2>
<p>To understand why having two pairs of lobes is unusual, we first need to understand what creates the lobes.</p>
<p>Nearly all big galaxies have a supermassive black hole at their centre. </p>
<p>In an active galaxy, powerful jets of charged particles can emerge from the area around the supermassive black hole. Astronomers believe these are emitted from near the poles of the black hole, which is why there are two of them, and they usually point in opposite directions.</p>
<p>When the black hole’s activity stops, the jets stop growing and the material in them flows back towards the centre. Thus, what we see as one lobe of a radio galaxy is made up of both a jet spurting out, and the backflow material.</p>
<h2>A mystery solved</h2>
<p>In the past, there were two major theories for why PKS 2014-55 has two pairs of lobes. </p>
<p>The first suggested there were actually <em>two</em> massive active black holes at the galaxy’s centre, each emitting two <a href="https://blog.galaxyzoo.org/2014/01/22/how-do-black-holes-form-jets/">powerful jets</a>. </p>
<p>The second theory suggested the supermassive black hole had undergone a <a href="https://en.wikipedia.org/wiki/Spin-flip">spin flip</a>. This is when a rotating black hole’s spin axis has a sudden change in orientation, resulting in a second pair of jets at a different angle from the first pair.</p>
<p>But the recent observations from the South African MeerKAT telescope strongly suggest a third possibility: that the two larger lobes are the fast-moving particles zooming out from the black hole, while the two smaller lobes are the backflow looping around to fall back in.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/334263/original/file-20200512-175262-bogw1y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/334263/original/file-20200512-175262-bogw1y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/334263/original/file-20200512-175262-bogw1y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=335&fit=crop&dpr=1 600w, https://images.theconversation.com/files/334263/original/file-20200512-175262-bogw1y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=335&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/334263/original/file-20200512-175262-bogw1y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=335&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/334263/original/file-20200512-175262-bogw1y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=420&fit=crop&dpr=1 754w, https://images.theconversation.com/files/334263/original/file-20200512-175262-bogw1y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=420&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/334263/original/file-20200512-175262-bogw1y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=420&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 South African Radio Astronomy Observatory’s MeerKAT telescope array consists of 64 radio dishes (pictured). Computers combine signals from these antennas to synthesise a telescope eight kilometres in diameter.</span>
<span class="attribution"><span class="source">SARAO/Author provided (no reuse)</span></span>
</figcaption>
</figure>
<p>The MeerKAT team achieved high-resolution images ten times more sensitive than our ASKAP pilot observations conducted here in Australia last year. </p>
<h2>A cosmic wonder</h2>
<p>Using <a href="https://www.csiro.au/en/Research/Facilities/ATNF/ASKAP">CSIRO’s ASKAP</a> telescope, our team observed the “purple butterfly” of PKS 2014-55 to be an enormous cosmic structure. It spans at least five million light years – about 20 times the size of our own Milky Way galaxy. </p>
<p>PKS 2014-55 is located on the outskirts of a massive cluster of galaxies known as Abell 3667. It was discovered more than 60 years ago using the <a href="https://www.atnf.csiro.au/news/newsletter/jun02/Flowering_of_Fleurs.htm">Mills Cross Telescope</a> at CSIRO’s old <a href="https://www.environment.nsw.gov.au/heritageapp/ViewHeritageItemDetails.aspx?id=2260832">Fleurs field station</a> in New South Wales. </p>
<p>The galaxy was first seen by <a href="https://www.atnf.csiro.au/people/rekers/">Ron Ekers</a> using the <a href="https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/parkes-interferometer/9EB4F096050C7F3A8020E3770444C1E7">Parkes Interferometer</a> in 1969.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-brain-transplant-for-one-of-australias-top-telescopes-129138">A brain transplant for one of Australia's top telescopes</a>
</strong>
</em>
</p>
<hr>
<h2>ASKAP</h2>
<p>The ASKAP telescope we used to capture PKS 2014-55 is an array of 36 radio dishes laid out in a pattern six kilometres in diameter. Together, the dishes make up a large radio telescope that uses Earth’s rotation to produce sharp images of astronomical sources near and far. </p>
<p>Each dish is 12m wide and <a href="https://www.csiro.au/en/Research/Astronomy/ASKAP-and-the-Square-Kilometre-Array/PAFs">equipped</a> with new technologies developed by CSIRO and industry partners. ASKAP is a fast survey machine, taking radio images over very wide areas of the sky. Several surveys of the entire sky are expected to start next year.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/333671/original/file-20200508-49546-110hle4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/333671/original/file-20200508-49546-110hle4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=298&fit=crop&dpr=1 600w, https://images.theconversation.com/files/333671/original/file-20200508-49546-110hle4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=298&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/333671/original/file-20200508-49546-110hle4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=298&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/333671/original/file-20200508-49546-110hle4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=375&fit=crop&dpr=1 754w, https://images.theconversation.com/files/333671/original/file-20200508-49546-110hle4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=375&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/333671/original/file-20200508-49546-110hle4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=375&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Australian Square Kilometre Array (ASKAP) radio telescope, located in the Murchison Shire in Western Australia.</span>
</figcaption>
</figure>
<hr>
<p><em>We acknowledge the Wajarri Yamatji as the traditional owners of the Murchison Radio-astronomy Observatory site.</em></p><img src="https://counter.theconversation.com/content/138205/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Baerbel Koribalski 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>Like a cosmic butterfly in the sky, radio galaxy PKS 2014-55 was observed by CSIRO researchers with the Australian SKA Pathfinder telescope.Baerbel Koribalski, Senior research scientist, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1210172019-08-08T09:30:09Z2019-08-08T09:30:09ZKepler’s forgotten ideas about symmetry help explain spiral galaxies without the need for dark matter – new research<figure><img src="https://images.theconversation.com/files/285739/original/file-20190725-136728-aaxtby.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">M81 spiral galaxy.</span> <span class="attribution"><span class="source">NASA/JPL-Caltech/ESA/Harvard-Smithsonian CfA</span></span></figcaption></figure><p>The 17th-century astronomer <a href="https://doi.org/10.3189/S0022143000020013">Johannes Kepler</a> was the first to muse about the structure of snowflakes. Why are they so symmetrical? How does one side know how long the opposite side has grown? Kepler thought it was all down to what we would now call a <a href="https://en.wikipedia.org/wiki/Morphogenetic_field">“morphogenic field”</a> – that things <em>want</em> to have the form they have. Science has since discounted this idea. But the question of why snowflakes and similar structures are so symmetrical is nevertheless not entirely understood.</p>
<p>Modern science shows just how fundamental the question is: look at all the spiral galaxies out there. They can be half a million light years across, but they still preserve their symmetry. How? In our <a href="http://dx.doi.org/10.1038/s41598-019-46765-w">new study</a>, published in <a href="https://www.nature.com/srep/">Scientific Reports</a>, we present an explanation. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/285911/original/file-20190726-43126-170umci.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/285911/original/file-20190726-43126-170umci.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=429&fit=crop&dpr=1 600w, https://images.theconversation.com/files/285911/original/file-20190726-43126-170umci.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=429&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/285911/original/file-20190726-43126-170umci.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=429&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/285911/original/file-20190726-43126-170umci.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=539&fit=crop&dpr=1 754w, https://images.theconversation.com/files/285911/original/file-20190726-43126-170umci.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=539&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/285911/original/file-20190726-43126-170umci.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=539&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Real snowflake.</span>
<span class="attribution"><span class="source">Karen Schanely: https://www.clickinmoms.com/blog/take-macro-snowflakes-pictures/; public domain</span></span>
</figcaption>
</figure>
<p>We have shown that information and “entropy” – a measure of the disorder of a system – are linked together (“info-entropy”) in a way exactly analogous to electric and magnetic fields (“electromagnetism”). Electric currents produce magnetic fields, while changing magnetic fields produce electric currents. Information and entropy influence each other in the same way.</p>
<p>Entropy is a fundamental concept in physics. For example, because entropy can never decrease (disorder always increases) you can turn an egg into scrambled eggs but not the other way around. If you move information around you must also increase entropy – a phone call has <a href="https://eandt.theiet.org/content/articles/2010/07/entropy-analysis-threatens-to-turn-efficient-computing-on-its-head/">an entropy cost</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/287340/original/file-20190808-144888-x8ziyr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/287340/original/file-20190808-144888-x8ziyr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=318&fit=crop&dpr=1 600w, https://images.theconversation.com/files/287340/original/file-20190808-144888-x8ziyr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=318&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/287340/original/file-20190808-144888-x8ziyr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=318&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/287340/original/file-20190808-144888-x8ziyr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=400&fit=crop&dpr=1 754w, https://images.theconversation.com/files/287340/original/file-20190808-144888-x8ziyr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=400&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/287340/original/file-20190808-144888-x8ziyr.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=400&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Light wave with electric (E) and magnetic (B) fields.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We showed that entropy and information can be treated as a field and that they are related to geometry. Think of the two strands of the <a href="https://en.wikipedia.org/wiki/DNA">DNA</a> double helix winding around each other. Light waves <a href="https://en.wikipedia.org/wiki/Electromagnetic_radiation">have the same structure</a>, where the two strands are the electric and magnetic fields. We showed mathematically that the relationship between information and entropy can be visualised using just the same geometry.</p>
<p>We wanted to see if our theory could predict things in the real world, and decided to try and calculate how much energy you’d need to convert one form of DNA to another. DNA is after all a spiral and a form of information. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/285875/original/file-20190726-43114-9fk0s3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/285875/original/file-20190726-43114-9fk0s3.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=252&fit=crop&dpr=1 600w, https://images.theconversation.com/files/285875/original/file-20190726-43114-9fk0s3.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=252&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/285875/original/file-20190726-43114-9fk0s3.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=252&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/285875/original/file-20190726-43114-9fk0s3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=316&fit=crop&dpr=1 754w, https://images.theconversation.com/files/285875/original/file-20190726-43114-9fk0s3.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=316&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/285875/original/file-20190726-43114-9fk0s3.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=316&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Two forms of DNA.</span>
<span class="attribution"><span class="source">Parker & Jeynes, Fig.1 of Scientific Reports 9|10779 (2019); Modified from Fig. 5 of Allemand et al. Proc. Natl. Acad. Sci. USA 95, 14152–14157 (1998)</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>This was actually done in extraordinarily precise <a href="http://dx.doi.org/10.1038/nature01810">measurements</a> some 16 years ago. The researchers pulled a DNA molecule straight (DNA likes to curl up), and twisted it 4,800 turns while holding the ends with <a href="https://theconversation.com/arthur-ashkins-optical-tweezers-the-nobel-prize-winning-technology-that-changed-biology-104282">optical tweezers</a>. The DNA flipped from one form to another, as in the picture above. The researchers could then calculate the energy difference between the two forms. </p>
<p>But our theory could calculate this energy difference, too. We knew the entropy of each of the two versions of this DNA molecule, and the energy is simply the product of entropy and temperature. Our result was spot on – the theory seemed to hold up.</p>
<h2>From tiny to enormous</h2>
<p>Spiral galaxies are double spirals just as DNA is a double helix – mathematically speaking they have similar geometries. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/285831/original/file-20190726-43153-1ru6eaz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/285831/original/file-20190726-43153-1ru6eaz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=383&fit=crop&dpr=1 600w, https://images.theconversation.com/files/285831/original/file-20190726-43153-1ru6eaz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=383&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/285831/original/file-20190726-43153-1ru6eaz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=383&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/285831/original/file-20190726-43153-1ru6eaz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/285831/original/file-20190726-43153-1ru6eaz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/285831/original/file-20190726-43153-1ru6eaz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=482&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A spiral galaxy with an overlaid double-armed logarithmic spiral.</span>
<span class="attribution"><span class="source">Parker & Jeynes, Fig.2 of Scientific Reports 9|10779 (2019)</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Our theory shows directly why the two arms of the spiral galaxies are symmetrical – it’s because info-entropy fields give rise to forces (like other fields). The stars in the galaxy are simply choreographed by an entropic force to line up into a pair of such spirals to maximise entropy.</p>
<p>But we wanted to get some real numbers, too. We therefore decided to try to calculate the mass of our galaxy from our theory. We know how heavy the Milky Way appears to be from how fast the stars move near the galactic edge – it is about 1.3 trillion sun masses.</p>
<p>Strangely, this is actually much more than the mass of all the visible stars in the galaxy. To be able to explain this discrepancy and account for why stars move so much faster than expected, astronomers came up with the idea of “<a href="https://theconversation.com/from-machos-to-wimps-meet-the-top-five-candidates-for-dark-matter-51516">dark matter</a>” – unseen mass lurking in the galaxy, increasing its gravitational pull on the stars.</p>
<p>We needed to know the entropy of the galaxy for our calculations. Luckily, the mathematical physicist <a href="https://en.wikipedia.org/wiki/Roger_Penrose">Roger Penrose</a> showed that <a href="https://en.wikipedia.org/wiki/Cycles_of_Time">this entropy</a> is dominated by the entropy of its central <a href="https://en.wikipedia.org/wiki/Supermassive_black_hole">super-massive black hole</a>.</p>
<p>We know the mass of this black hole (4.3m sun masses). And amazingly, when you know the mass of a black hole, there is an <a href="http://www.scholarpedia.org/article/Bekenstein-Hawking_entropy">equation</a>, discovered by the late physicist <a href="https://en.wikipedia.org/wiki/Stephen_Hawking">Stephen Hawking</a>, that calculates its entropy. Hawking also discovered how to calculate the <a href="https://en.wikipedia.org/wiki/Hawking_radiation">“temperature” at its surface, or “event horizon”</a>.</p>
<p>If you can assign a “temperature” to the black hole event horizon – which has no stuff in it to have temperature – why not also assign a temperature to a galaxy? We argue in our paper that this is reasonable (using what’s known as the <a href="https://www.scientificamerican.com/article/sidebar-the-holographic-p/">“holographic principle”</a>). So we used our info-entropy equations to calculate the galaxy’s holographic temperature. </p>
<p>Then it gets easy. We know that the galactic energy is given by the product of its entropy and temperature. And when we know the energy we can find out the mass thanks to <a href="https://www.britannica.com/science/E-mc2-equation">Einstein’s famous equation</a>: E=mc<sup>2</sup>.</p>
<p>This time the result was not exactly spot on, but it was reasonably close given our highly simplified model of the galaxy. The info-entropic geometry of a galaxy not only explains how entropic forces create the beautifully symmetric shape and keep it, but also accounts for all the mass that appears to be evident in it. </p>
<p>This means that we don’t actually need dark matter after all. According to our model, the galactic entropy gives rise to such a large quantity of additional energy that it modifies the observed dynamics of the galaxy – making stars at the edge move faster than expected. This is exactly what dark matter was meant to explain. The energy isn’t directly observable as mass, but its presence is certainly supported by the astronomical observations – explaining why dark matter searches have so far found nothing. </p>
<p>There is a lot of research supporting the idea of dark matter though. Our theory suggests an alternative explanation of the observations, and needs no new physics. Of course, more detailed work is needed to verify that the true complexity of the observations can also be modelled successfully.</p>
<p>We think that the “morphogenic field” Kepler was seeking really does exist, and is actually the effect of the intertwining of information and entropy. After four long centuries, it seems Kepler has finally been vindicated.</p><img src="https://counter.theconversation.com/content/121017/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors 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>New research does away with dark matter by putting ‘entropy’, a measure of disorder, at the heart of the universe.Chris Jeynes, Senior researcher, University of SurreyMichael Parker, Visiting Fellow, University of EssexLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1198612019-07-11T12:55:43Z2019-07-11T12:55:43ZJoy Division: 40 years on from ‘Unknown Pleasures’, astronomers have revisited the pulsar from the iconic album cover<figure><img src="https://images.theconversation.com/files/283650/original/file-20190711-173325-1oj4n2t.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C6000%2C3314&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">'Unknown Pleasures' as you've never seen it before...</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/3d-illustration-rendering-black-white-line-1308510430?src=E285f9LBp2pjGmUMJk8lMw-1-49&studio=1">Freeda/Shutterstock</a></span></figcaption></figure><p>The English rock band Joy Division released their debut studio album “Unknown Pleasures” 40 years ago. The front cover doesn’t feature any words, only a now iconic black and white data graph showing 80 wiggly lines representing a signal from a pulsar in space. To mark the anniversary of the album, we recorded a signal from the same pulsar with a radio telescope in Jodrell Bank Observatory, only 14 miles (23 km) away from Strawberry Studios where the album was recorded.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"497303154279845888"}"></div></p>
<p>Peter Saville – graphic designer and co-founder of Factory Records – designed the album cover based on a picture spotted by band member Bernard Sumner in an encyclopaedia. The picture itself can be traced to the work of the postgraduate student Harold Craft, who published the image in his PhD thesis in 1970. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Recording of the same pulsar, exactly 40 years after the album was released.</span>
<span class="attribution"><span class="source">Jodrell Bank Centre for Astrophysics, University of Manchester</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Unknown treasures in space</h2>
<p>What we see in this enigmatic image is the signal produced by a pulsar known as B1919+21, the first pulsar ever discovered. A pulsar is formed during the violent death of a star several times more massive than our sun. These stars go out with a bang known as a “supernova explosion”, during which the core of the exploding star is compressed in an almost perfect sphere with a radius of little more than 10 km. What’s formed is called a neutron star.</p>
<p>This stellar remnant, still more massive than our sun, is so extremely dense that the atoms from the original star cannot maintain their structure – they fall apart leaving smaller particles called neutrons, which form a vast ocean beneath the star’s crust. Pulsars are rapidly spinning neutron stars that can be observed from Earth. Thanks to their rotation and a magnetic field which is a trillion times stronger than that of the Earth, the magnetic north and south poles of these super magnets shine like a lighthouse. After having travelled for many hundreds of years, flashes of radiation from B1919+21 reach the Earth every 1.34 seconds.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1140000363367546882"}"></div></p>
<p>These flashes from pulsars are especially bright at radio wavelengths, so their signals can be recorded using radio telescopes. A radio telescope works similar to a radio in your car – its antenna focuses radio waves from space onto a point where they can be detected and turned into an electric signal, which can then be converted into sound. We used the Mark II radio telescope of the <a href="http://www.jb.man.ac.uk/research/pulsar/Education/Sounds/">Jodrell Bank Observatory</a> at the University of Manchester for our recording.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.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">The Mark II telescope at the Jodrell Bank Observatory which made a 47-minute recording of B1919+21.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Mark_II_(radio_telescope)#/media/File:Jodrell_Bank_Mark_II.jpg">Mike Peel/Jodrell Bank Centre for Astrophysics, University of Manchester</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The album cover shows 80 wiggly lines which correspond to 80 flashes of radio waves from B1919+21, as the neutron star made 80 turns in 107 seconds. Unlike lighthouses on Earth, each flash is unique. Some flashes are bright – these are denoted in the image by their large spikes – and some are dim. </p>
<p>The shape of the pulses are ever changing. At first glance, they seem irregular and chaotic, but our new imaging reveals some order in the chaos. It’s the same number of pulses from the same pulsar and observed at the same frequency as the diagram from the album cover, but in the image below, a diagonal pattern of stripes emerges.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=914&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=914&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=914&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1148&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1148&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1148&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 signal of the same pulsar as featured on the album cover. The lighter the colour is, the more intense the radio waves are.</span>
<span class="attribution"><span class="source">Jodrell Bank Centre for Astrophysics, University of Manchester</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>When the original signal was recorded, it was not known why some pulsars showed this kind of pattern. We now believe that the radio waves are produced by particles which shoot away from the neutron star at nearly the speed of light. The particles are created by electric discharges between the ionised gas surrounding these objects and the surface of the star itself. So, in essence, the radio waves on the album cover and in our new imaging are caused by lightning in outer space, observed many light years away. </p>
<p>A “weather map” can help visualise the vast lightning systems which circulate the magnetic poles of pulsars. The pattern of their lightning changes continuously and the shape of the observed pulses appear somewhat erratic – but observing over a longer period allows a pattern to emerge.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=599&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=599&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=599&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=752&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=752&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=752&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Looking down on the magnetic pole of pulsar B1919+21 which is encircled by lightning.</span>
<span class="attribution"><span class="source">Jodrell Bank Centre for Astrophysics, University of Manchester</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Four decades after the release of the Unknown Pleasures album we now understand much better what those wiggly lines on its cover mean. But many questions remain about these enigmatic objects, which in many respects are nature’s most extreme creation. Something which remained true for all these years is that pulsar recordings push us to explore the limits of our understanding of the laws of physics.</p><img src="https://counter.theconversation.com/content/119861/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Patrick Weltevrede receives funding from the UK Science and Technology Facilities Council (STFC)</span></em></p>When you look at the squiggly lines on Joy Division’s famous album cover, you’re seeing a record of lightning in outer space.Patrick Weltevrede, Lecturer In Pulsar Astrophysics, University of ManchesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1067272018-11-14T12:10:09Z2018-11-14T12:10:09ZHow we discovered that supermassive black holes can power enormous ‘galactic fountains’<figure><img src="https://images.theconversation.com/files/245518/original/file-20181114-194497-1ecfea6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist impression of Abell 2597.</span> <span class="attribution"><span class="source">NRAO AUI NSF D Berry</span></span></figcaption></figure><p>A fountain in a garden pond could shoot a plume of water to roughly three metres in height. By comparison, the <a href="https://www.thelocal.ch/20171027/ten-facts-about-genevas-famous-jet-deau">famous fountain on Lake Geneva</a> launches a plume of water up to 140m into the air. Now imagine a fountain launched from the centre of a galaxy, with a <a href="http://astronomy.swin.edu.au/cosmos/S/Supermassive+Black+Hole">supermassive black hole</a> acting as the pump. How far do you think this plume would extend? The answer is over 100,000 light years.</p>
<p>We know this as we have just spotted such a fountain – spewing out <a href="http://astronomy.swin.edu.au/cosmos/M/Molecular+Cloud">incredibly cold gas</a> rather than water – in a <a href="http://astronomy.swin.edu.au/cosmos/B/Brightest+Cluster+Galaxies">giant galaxy at the centre of a cluster of galaxies</a> known as Abell 2597. Astronomers have long believed that such fountains must exist in some galaxies – continually circulating fuel that can form stars. Now our findings, <a href="http://iopscience.iop.org/article/10.3847/1538-4357/aad6dd">published in The Astrophysical Journal</a>, finally prove they do exist in nature.</p>
<p>We were able to view this spectacle in its full glory by combining observations from two of the worlds most powerful telescopes, the Atacama Large Millimetre Array (<a href="https://www.eso.org/public/unitedkingdom/teles-instr/alma/">ALMA</a>) and the Multi Unit Spectroscopic Explorer (<a href="https://www.eso.org/sci/facilities/paranal/instruments/muse/overview.html">MUSE</a>). MUSE showed the gas being pumped out and reaching the top of the plume, while ALMA revealed how it thereafter rained back down into the supermassive black hole (an extremely large black hole), triggering the whole process over again. The power of the event is phenomenal. The fountain is in fact lifting more than 3 billion <a href="http://astronomy.swin.edu.au/cosmos/S/Solar+Mass">solar masses</a> of cold gas from its centre.</p>
<h2>Galaxy maintenance</h2>
<p>Our international team of astronomers chose to look at this particular galaxy, which is located a billion light years away from us, because of its position at the centre of a cluster of galaxies. Such clusters are <a href="http://chandra.harvard.edu/learn_galaxyCluster.html">filled with extremely hot gas</a> at more than 10m degrees, known as the <a href="https://en.wikipedia.org/wiki/Intracluster_medium">intracluster medium</a>. We know that this hot gas can cool very quickly – and when it does it produces massive amounts of star forming fuel for galaxies at the centre of the cluster, such as this one.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/245519/original/file-20181114-194488-1m2q2ex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/245519/original/file-20181114-194488-1m2q2ex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=602&fit=crop&dpr=1 600w, https://images.theconversation.com/files/245519/original/file-20181114-194488-1m2q2ex.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=602&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/245519/original/file-20181114-194488-1m2q2ex.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=602&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/245519/original/file-20181114-194488-1m2q2ex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=756&fit=crop&dpr=1 754w, https://images.theconversation.com/files/245519/original/file-20181114-194488-1m2q2ex.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=756&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/245519/original/file-20181114-194488-1m2q2ex.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=756&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Image of the Abell 2597 galaxy cluster showing the fountain-like flow of gas in the central galaxy. The yellow is ALMA data showing cold gas.</span>
<span class="attribution"><span class="source">ALMA (ESO/NAOJ/NRAO), Tremblay et al.; NRAO/AUI/NSF, B. Saxton; NASA/Chandra; ESO/VLT</span></span>
</figcaption>
</figure>
<p>Left unchecked, this can result in an enormous burst of star formation within the central galaxy, producing up to <a href="https://astronomynow.com/2017/02/16/astronomers-observe-black-hole-producing-cold-starmaking-fuel/">1,000 new stars the size of our sun every year</a>. But astronomers typically only measure star formation rates at <a href="http://iopscience.iop.org/article/10.1086/588212/meta">less than 1% of this in such galaxies</a> . Our discovery finally demonstrates why – it’s the effect of the fountain continually cycling the star forming fuel. This stops the gas forming stars and <a href="https://www.annualreviews.org/doi/full/10.1146/annurev.astro.45.051806.110625">keeps the galaxy from growing too big</a> too fast.</p>
<p>The process, called mechanical feedback, takes place when the black hole <a href="https://theconversation.com/how-we-discovered-the-strange-physics-of-jets-from-supermassive-black-holes-92390">launches “jets”</a> – two streams of plasma (matter made up of electrically charged particles despite having no overall charge), travelling in opposite directions at velocities very close to the speed of light. The jets, which astronomers have known about for some time, inflate enormous bubbles in the surrounding hot gas. As these bubbles rise, they lift the colder gas out of the galaxy, producing the plume of the fountain. But the gas does not move quickly enough to escape the galaxy’s gravity, eventually raining back down onto it.</p>
<p>What was lacking from this picture though, was knowledge about how the jets from the black hole were powered. Some gas had to be falling into the black hole, releasing huge amounts of energy and driving the outbursts. With ALMA we were able to complete the picture, showing that gas clouds at less than 300 light years from the black hole are falling towards it due to its immense gravity. Taken together with the MUSE data, our study is the first compelling evidence for the simultaneous inflow and outflow of gas around a supermassive black hole – representing the full cycle of the fountain. </p>
<h2>More fountains?</h2>
<p>While we’ve only spotted one fountain, the process is likely to be at play in other similar galaxies at the centre of clusters. We know these galaxies have changed little over the past few billion years, despite the abundance of fuel to potentially form stars. By continually cycling the star forming fuel, galaxy fountains help to keep them so stable.</p>
<p>The process may actually affect all galaxies at some point in their lives. That’s because all galaxies have some cooling gas to fuel such fountains. However galaxies far from the centre of a cluster are likely to have less cooling gas available, so their fountains will be smaller and only shortlived. </p>
<p>Still, given there could be more than 200 billion galaxies in the universe, there are probably a lot of galaxy fountains out there.</p><img src="https://counter.theconversation.com/content/106727/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stephen Hamer works for the University of Bath in the Department of Physics. He has previously received funding from the European Research Council to study feedback in galaxies and galaxy clusters. He is affiliated with the MUSE consortium, an international team of scientists who support MUSE development and work to utilize the data it provides to further our understanding of the Universe. </span></em></p>Astronomers have suspected them for ages –now a team as finally spotted a ‘fountain’ in a galaxy far, far away.Stephen Hamer, Postdoctoral Researcher of Astrophysics, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/985622018-11-06T23:06:51Z2018-11-06T23:06:51ZCurious Kids: Are there living things on different galaxies?<figure><img src="https://images.theconversation.com/files/223749/original/file-20180619-126537-5l632j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Nobody knows for sure - but it's possible. </span> <span class="attribution"><a class="source" href="http://www.shutterstock.com">Shutterstock</a></span></figcaption></figure><p><em>This is an article from <a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a>, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!</em> </p>
<hr>
<blockquote>
<p><strong>Are there living things on different galaxies? – Annabel, age 6, Turramurra.</strong> </p>
</blockquote>
<hr>
<p>That’s a fantastic question, Annabel – and one scientists are desperate to answer. The short answer is that we simply don’t know. Many people suspect there must be life beyond the Earth, but we haven’t found any evidence yet.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-what-plants-could-grow-in-the-goldilocks-zone-of-space-76918">Curious Kids: What plants could grow in the Goldilocks zone of space?</a>
</strong>
</em>
</p>
<hr>
<p>The fact that we haven’t found life elsewhere <em>yet</em> <strong>doesn’t</strong> mean that such life does not exist. Searching for life is really hard, even in the Solar system, so it could be that there is life very near by. We just haven’t found it yet.</p>
<p>My own guess is that there probably is life elsewhere in the Universe – and the reason for that is just how ginormous the universe is. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-why-do-stars-twinkle-81188">Curious Kids: Why do stars twinkle?</a>
</strong>
</em>
</p>
<hr>
<h2>In our Solar system alone, there are lots of places life could exist</h2>
<p>Let’s go for a tour of the Universe, starting at home, <a href="https://solarsystem.nasa.gov/">in the Solar system</a>…</p>
<p>When you learn about the Solar system at school, you’ll learn about the eight planets – <a href="https://solarsystem.nasa.gov/planets/mercury/overview/">Mercury</a>, <a href="https://solarsystem.nasa.gov/planets/venus/overview/">Venus</a>, <a href="https://solarsystem.nasa.gov/planets/earth/overview/">Earth</a>, <a href="https://solarsystem.nasa.gov/planets/mars/overview/">Mars</a>, <a href="https://solarsystem.nasa.gov/planets/jupiter/overview/">Jupiter</a>, <a href="https://solarsystem.nasa.gov/planets/saturn/overview/">Saturn</a>, <a href="https://solarsystem.nasa.gov/planets/uranus/overview/">Uranus</a> and <a href="https://solarsystem.nasa.gov/planets/neptune/overview/">Neptune</a> – and that’s probably about it. </p>
<p>In fact, the Solar system contains an immense number of objects. We know of hundreds of thousands of <a href="https://solarsystem.nasa.gov/small-bodies/asteroids/overview">asteroids</a>, and think there may be more than ten trillion <a href="https://solarsystem.nasa.gov/small-bodies/comets/overview">comets</a>, held in cold storage around the Sun, halfway to the nearest star. Ten trillion is 10,000,000,000,000. That’s a lot of comets, all made of ice and dust! </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/239274/original/file-20181004-52695-1qeg3rh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/239274/original/file-20181004-52695-1qeg3rh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/239274/original/file-20181004-52695-1qeg3rh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/239274/original/file-20181004-52695-1qeg3rh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/239274/original/file-20181004-52695-1qeg3rh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/239274/original/file-20181004-52695-1qeg3rh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/239274/original/file-20181004-52695-1qeg3rh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/239274/original/file-20181004-52695-1qeg3rh.jpg?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">Comet McNaught is one of an estimated ten trillion dirty snowballs, all circling the Sun.</span>
<span class="attribution"><span class="source">ESO/Sebastian Deiries</span></span>
</figcaption>
</figure>
<p>Of the many objects in the Solar system, we think the best places to look for life are <a href="https://theconversation.com/water-water-everywhere-in-our-solar-system-but-what-does-that-mean-for-life-76315">those that have liquid water</a>, or had it in the past. Why? Well, on Earth, everywhere we find water we find life, so it seems natural to search where liquid water is present!</p>
<p>Mars is our main target, and we keep <a href="https://mars.nasa.gov/programmissions/missions/">sending spacecraft</a> to try to find out if there was ever life there. </p>
<p>But there are a growing number of other targets – moons orbiting the giant planets that have vast oceans of liquid water, buried deep underground. </p>
<p>Around Jupiter, we know that <a href="https://solarsystem.nasa.gov/moons/jupiter-moons/europa/in-depth/">Europa</a>, <a href="https://solarsystem.nasa.gov/moons/jupiter-moons/ganymede/in-depth/">Ganymede</a> and <a href="https://solarsystem.nasa.gov/moons/jupiter-moons/callisto/in-depth/">Callisto</a> have oceans, each of which has more water than the Earth. Saturn’s moons, too, have oceans – with tiny <a href="https://solarsystem.nasa.gov/moons/saturn-moons/enceladus/in-depth/">Enceladus</a> perhaps the most surprising place that we’ve found liquid water.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/239087/original/file-20181003-719-11q5upj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/239087/original/file-20181003-719-11q5upj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/239087/original/file-20181003-719-11q5upj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=867&fit=crop&dpr=1 600w, https://images.theconversation.com/files/239087/original/file-20181003-719-11q5upj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=867&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/239087/original/file-20181003-719-11q5upj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=867&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/239087/original/file-20181003-719-11q5upj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1089&fit=crop&dpr=1 754w, https://images.theconversation.com/files/239087/original/file-20181003-719-11q5upj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1089&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/239087/original/file-20181003-719-11q5upj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1089&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Saturn’s moon Enceladus – a surprising target in the search for life.</span>
<span class="attribution"><span class="source">NASA/JPL/Space Science Institute</span></span>
</figcaption>
</figure>
<p>So, in our Solar system alone, there are loads of places that we think life could exist – and we’re busy looking to see if it is there.</p>
<h2>A Universe full of planets</h2>
<p>But the Solar system is just one of an immense number of planetary systems. The Sun is one of around 400 billion stars in our galaxy, <a href="https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html">the Milky Way</a>. That’s 400,000,000,000 stars. And since I was a kid, we’ve learned that almost every star has planets.</p>
<p>What does this mean? Well, if we guess that each star has eight planets (like the Sun), then if there are 400,000,000,000 stars in the galaxy, there will be 3.2 trillion planets (3,200,000,000,000, which is 200 billion groups of eight). </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/239275/original/file-20181004-52695-dat4el.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/239275/original/file-20181004-52695-dat4el.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/239275/original/file-20181004-52695-dat4el.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/239275/original/file-20181004-52695-dat4el.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/239275/original/file-20181004-52695-dat4el.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/239275/original/file-20181004-52695-dat4el.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=498&fit=crop&dpr=1 754w, https://images.theconversation.com/files/239275/original/file-20181004-52695-dat4el.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=498&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/239275/original/file-20181004-52695-dat4el.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=498&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 now know that every star has planets - so there could be 3.2 trillion worlds out there in our galaxy - lots of room for life to thrive!</span>
<span class="attribution"><span class="source">ESO/M. Kornmesser</span></span>
</figcaption>
</figure>
<p>That’s a huge number of alien worlds to search, places where there could be life.</p>
<h2>A Universe full of galaxies</h2>
<p>But that’s still just the start. Our galaxy, the Milky Way, is a single “city” of stars, all clustering together.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/239276/original/file-20181004-52672-1glp4s0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/239276/original/file-20181004-52672-1glp4s0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/239276/original/file-20181004-52672-1glp4s0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=548&fit=crop&dpr=1 600w, https://images.theconversation.com/files/239276/original/file-20181004-52672-1glp4s0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=548&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/239276/original/file-20181004-52672-1glp4s0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=548&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/239276/original/file-20181004-52672-1glp4s0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=688&fit=crop&dpr=1 754w, https://images.theconversation.com/files/239276/original/file-20181004-52672-1glp4s0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=688&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/239276/original/file-20181004-52672-1glp4s0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=688&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 the Hubble Space Telescope stared at an ‘empty’ piece of the sky, it saw galaxies everywhere – just a tiny fraction of all those spread through the Universe!</span>
<span class="attribution"><span class="source">NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)</span></span>
</figcaption>
</figure>
<p>But there are many more galaxies out there. In fact, scientists think that there could be 3.2 septillion (3,200,000,000,000,000,000,000,000) planets, just in the bit of the universe we can see. </p>
<p>How big is that number? Well, that means there are more than a million planets in the universe for <em>every single grain of sand on our planet</em>.</p>
<h2>What does that mean for life?</h2>
<p>With so many planets, it’s hard to imagine that there is no life beyond Earth. There are simply so many places that could have life that I, personally, think there must be a ginormous number of inhabited planets through the universe. Probably billions, trillions, or even quadrillions!</p>
<p>But will we ever find out?</p>
<p>I’d really like to think so – but space is enormous, and the search will be really hard. If we find life in the near future, I’d bet on us finding it close to home, somewhere in the Solar system.</p>
<hr>
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<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Please tell us your name, age and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/98562/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner 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>There are probably more than a million planets in the universe for every single grain of sand on Earth. That’s a lot of planets. My guess is that there probably is life elsewhere in the Universe.Jonti Horner, Professor (Astrophysics), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1006582018-07-27T03:55:37Z2018-07-27T03:55:37ZEinstein’s theory of gravity tested by a star speeding past a supermassive black hole<figure><img src="https://images.theconversation.com/files/229532/original/file-20180727-106514-sfkcvb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist’s impression of the path of star S2 as it passes very close to the supermassive black hole at the centre of the Milky Way. The very strong gravitational field causes the colour of the star to shift slightly to the red. (Size and colour exaggerated for clarity.)</span> <span class="attribution"><a class="source" href="https://www.eso.org/public/images/eso1825a/">ESO/M. Kornmesser</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Astronomers have found evidence that the supermassive black hole thought to lurk at the heart of our galaxy displays the gravitational properties dictated by the <a href="https://www.newscientist.com/round-up/instant-expert-general-relativity/">general theory of relativity</a>. </p>
<p>The news was announced overnight at the European Southern Observatory (<a href="https://www.eso.org/public/australia/">ESO</a>), with the work published in the scientific journal <a href="https://arxiv.org/abs/1807.09409">Astronomy and Astrophysics</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/sizes-matters-for-black-hole-formation-but-theres-something-missing-in-the-middle-ground-79576">Sizes matters for black hole formation, but there's something missing in the middle ground</a>
</strong>
</em>
</p>
<hr>
<p>By accurately tracing the position and speed of a single star (known as S2), astronomers have detected the telltale signature of Einstein’s gravity in action. </p>
<h2>Newton vs Einstein: weak vs strong</h2>
<p>Newton’s <a href="https://science.howstuffworks.com/environmental/earth/geophysics/question2321.htm">mathematical description of gravity</a> reigned for 250 years, but a century ago Einstein’s insights into the nature of space and time rewrote our gravitational understanding. </p>
<p>For most places in the universe, where gravitational fields are weak, the mathematics of Newton and Einstein give identical results for the motion of galaxies, stars and planets. </p>
<p>But as the strength of gravity increases, subtle differences between the two theories emerge. </p>
<p>In fact, Einstein was guided by small but significant discrepancies in the <a href="http://physics.ucr.edu/%7Ewudka/Physics7/Notes_www/node98.html">orbit of Mercury</a> about the Sun while reworking his vision of gravity.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/229541/original/file-20180727-106521-1r9ujk3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229541/original/file-20180727-106521-1r9ujk3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229541/original/file-20180727-106521-1r9ujk3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=366&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229541/original/file-20180727-106521-1r9ujk3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=366&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229541/original/file-20180727-106521-1r9ujk3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=366&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229541/original/file-20180727-106521-1r9ujk3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=460&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229541/original/file-20180727-106521-1r9ujk3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=460&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229541/original/file-20180727-106521-1r9ujk3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=460&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Stars in orbit around a supermassive black hole, the ideal laboratory to test Einstein’s general theory of relativity.</span>
<span class="attribution"><a class="source" href="https://www.eso.org/public/images/eso1825d/">ESO/L. Calçada/spaceengine.org</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>For more than two decades astronomers have charted the orbits of stars around an apparent nothingness lurking at the heart of our Milky Way. An immense amount of mass, more than four million times the mass of the Sun, must be present to keep the stars on course.</p>
<p>That mass is concentrated into a tiny volume. Astronomers have only one candidate for such a monster: a black hole. This is a region of completely collapsed mass, known to exist as a consequence of Einstein’s vision of gravity. </p>
<h2>The star to follow</h2>
<p>While the motions of stars at the galaxy’s centre revealed the presence of the black hole, astronomers wondered if they could search for particular signatures of Einstein’s gravity by tracking their orbits. </p>
<p>For most stars this isn’t possible as they are far enough away from the black hole, where the gravitational pull weakens. Their orbits should therefore agree with both Newton and Einstein. </p>
<p>But one star, S2, possessed a tantalising, highly elliptical orbit. It passes close to the black hole every 16 years, at a distance of less than 20 billion km (only three times the orbit of Pluto within our Solar System). That’s a tiny distance on galactic scales.</p>
<p>The star travels at a blistering 7,600km per second, roughly 3% of the speed of light.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Eysecnh7yqc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">ESO/L. Calçada/spaceengine.org.</span></figcaption>
</figure>
<p>If astronomers could accurately trace S2 through the closest approach of its orbit - where the effects of general relativity should be strongest - the differences between the gravitational theories of Newton and Einstein should become apparent. </p>
<h2>Pushing telescopes to the limit</h2>
<p>Observing stars at the centre of the Milky Way is not easy. It’s a dusty and crowded field of view and the blurring of the Earth’s atmosphere introduces too much distortion. Could measurements be made that were precise enough to test the nature of gravity?</p>
<p>Astronomers are not easily daunted and they had time to prepare. They called on the Very Large Telescope (<a href="http://www.eso.org/public/australia/teles-instr/paranal-observatory/vlt/">VLT</a>), consisting of four 8-metre telescopes in the mountains of Chile. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/229546/original/file-20180727-106524-6ximzy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229546/original/file-20180727-106524-6ximzy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229546/original/file-20180727-106524-6ximzy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229546/original/file-20180727-106524-6ximzy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229546/original/file-20180727-106524-6ximzy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229546/original/file-20180727-106524-6ximzy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229546/original/file-20180727-106524-6ximzy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229546/original/file-20180727-106524-6ximzy.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">The Very Large Telescope using a Laser Guide Star (artificial star) as part of its adaptive optics system.</span>
<span class="attribution"><a class="source" href="https://www.eso.org/public/images/vlt-brunier-nuit/">ESO/S. Brunier</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The light from the individual telescopes is combined to act as one immense mirror, a technique known as <a href="http://www.eso.org/public/australia/teles-instr/technology/interferometry/">interferometry</a>. This sharpens the resolution of the images and provides much needed fine-level detail.</p>
<p>To improve accuracy even further, the telescopes were fitted with <a href="https://www.eso.org/public/australia/teles-instr/technology/adaptive_optics/">adaptive optics</a> to counter the effect of atmospheric blurring. They are also fitted with sensitive detectors to collect the light from individual stars. </p>
<p>With names such as <a href="http://www.eso.org/public/australia/teles-instr/paranal-observatory/vlt/vlt-instr/gravity/">GRAVITY</a>, <a href="http://www.eso.org/public/australia/teles-instr/paranal-observatory/vlt/vlt-instr/sinfoni/">SINFONI</a> and <a href="http://www.eso.org/public/australia/teles-instr/paranal-observatory/vlt/vlt-instr/naco/">NACO</a>, each represents an immensely complex instrument, built through the efforts of large teams of astronomers and engineers over many years. </p>
<h2>Let the observations begin</h2>
<p>In May 2018, when S2 was passing closest to the black hole, the team of astronomers were prepared.</p>
<p>The speed of S2 was monitored using <a href="http://astronomy.swin.edu.au/cosmos/D/Doppler+Shift">Doppler shift</a>, which tracks changes in the speed of the star by detecting small shifts in the wavelength of light emitted by the star. </p>
<p>The Doppler shift increased as the star approached the black hole and its motion initially agreed with the predictions of Newtonian gravity.</p>
<p>But as it drew closer still, the star seemed to increase in speed, peaking at more than 200km/s faster than expected.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/229543/original/file-20180727-106496-1f5211o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229543/original/file-20180727-106496-1f5211o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229543/original/file-20180727-106496-1f5211o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229543/original/file-20180727-106496-1f5211o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229543/original/file-20180727-106496-1f5211o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229543/original/file-20180727-106496-1f5211o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=473&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229543/original/file-20180727-106496-1f5211o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=473&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229543/original/file-20180727-106496-1f5211o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=473&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Under extreme gravity as it passes the black hole, the star S2 is slightly reddened (exaggerated here) just as Einstein predicted.</span>
<span class="attribution"><a class="source" href="https://www.eso.org/public/images/eso1825b/">ESO/M. Kornmesser</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>This extra speed was not due to an actual increase in motion. Another effect was in play, as the light from the star had to fight against the increased pull of gravity. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-where-do-black-holes-lead-to-98557">Curious Kids: Where do black holes lead to?</a>
</strong>
</em>
</p>
<hr>
<p>Called <a href="http://astronomy.swin.edu.au/cosmos/G/Gravitational+Redshift">gravitational redshift</a>, this effect was predicted by Einstein more than a century ago. The star’s light was being stretched to longer (or redder) wavelengths, and the detected distortion matched expectations of a high-speed star zooming past a black hole. </p>
<p>These new observations are exciting and show that we are entering a new era of black hole research. With ever increasing accuracy, the general theory of relativity can be tested with more precision.</p>
<p>Some astronomers hope that these measurements will become so precise as to eventually show discrepancies that go against the general theory of relativity, ushering in a revolution in our understanding of gravity. Until that day, Einstein’s vision of space and time reigns supreme.</p><img src="https://counter.theconversation.com/content/100658/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tanya Hill is the Australian representative of the European Southern Observatory's Science Outreach Network.</span></em></p><p class="fine-print"><em><span>Geraint Lewis receives funding from the Australian Research Council.</span></em></p>Astronomers traced a single star as it passed close to the black hole at the centre of our galaxy, and detected the telltale signature of Einstein’s gravity in action.Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museums Victoria Research InstituteGeraint Lewis, Professor of Astrophysics, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/997852018-07-12T15:03:53Z2018-07-12T15:03:53ZScientists discover a new source of neutrinos in space – opening up another window into the universe<figure><img src="https://images.theconversation.com/files/227377/original/file-20180712-27015-1c0dy1f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression based on real picture of Icecube lab.</span> <span class="attribution"><span class="source">IceCube/NSF</span></span></figcaption></figure><p>Neutrinos – extremely light, ghostly particles that barely interact with matter – have so far only been observed originating from supernovae (exploding stars) and the sun. Now a giant detector at the South Pole has discovered that a “blazar”, a galaxy with a supermassive black hole at its centre, also produces neutrinos.</p>
<p>This is the first time a source of neutrinos in space has been discovered in more than 30 years. What’s more, it’s the first time scientists have observed a neutrino particle with high energy associated with an astrophysical event. This is really exciting news. The observation, <a href="http://science.sciencemag.org/cgi/doi/10.1126/science.aat2890">just published in Science</a>, opens a completely new chapter in neutrino astronomy.</p>
<p>Neutrinos are fundamental matter particles. The ordinary matter that we are all familiar with is made out of electrons and quarks. We do not observe neutrinos in daily life as they are extremely hard to detect. Theoretical physicist <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1945/pauli-bio.html">Wolfgang Pauli</a> suggested their existence in 1930, but it took until 1956 before they were first seen by experimental physicists <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1995/illpres/neutrino.html">coming from a nuclear reactor</a>.</p>
<p>The reason that they are so hard to detect is because they only weakly interact with ordinary matter. Most neutrinos fly straight through the Earth: they do not interact at all. They do, however, play a very important role in the universe. </p>
<p>For example, when a heavy star explodes at the end of its life, it is known as a supernova – as it shows up as an extremely bright and seemingly new star in the sky. We now know that supernovae emit many more neutrinos than photons (light particles), which we cannot see by eye. Scientists detected the first <a href="https://www.nasa.gov/feature/goddard/2017/the-dawn-of-a-new-era-for-supernova-1987a">neutrinos from a supernova in 1987</a> when a star collapsed just outside our Milky Way.
This unique observation has given us a better understanding of supernovae, as well as the properties of neutrinos themselves. </p>
<p>This event marked the birth of what we call neutrino astronomy. Powerful neutrino telescopes were built soon after. One of them was the <a href="https://www.sno.phy.queensu.ca/">Sudbury Neutrino Observatory (SNO)</a>. Physicist Art McDonald <a href="https://theconversation.com/how-the-neutrino-could-solve-great-cosmic-mysteries-and-win-its-next-nobel-prize-48789">received the Nobel Prize for Physics in 2015</a> for the detailed studies of solar neutrinos that he and his team did using this observatory, and the insights this gave us into the properties of the neutrino particles. </p>
<h2>Arctic analysis</h2>
<p>Another telescope has now grown to be the largest of them all. <a href="https://icecube.wisc.edu/">The IceCube experiment at the South Pole</a> is a cubic kilometre in size and uses deep arctic ice as a target for the neutrinos. Although neutrinos typically don’t interact with anything, they can produce a charged particle when they occasionally do interact with the fundamental particles that make up ice. In IceCube, this resulting particle travels through the ice and produces a trail of faint light. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/227379/original/file-20180712-27021-1p7f1nz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/227379/original/file-20180712-27021-1p7f1nz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=159&fit=crop&dpr=1 600w, https://images.theconversation.com/files/227379/original/file-20180712-27021-1p7f1nz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=159&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/227379/original/file-20180712-27021-1p7f1nz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=159&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/227379/original/file-20180712-27021-1p7f1nz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=199&fit=crop&dpr=1 754w, https://images.theconversation.com/files/227379/original/file-20180712-27021-1p7f1nz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=199&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/227379/original/file-20180712-27021-1p7f1nz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=199&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">IceCube drilling tower and hose reel in December 2009.</span>
<span class="attribution"><span class="source">Amble/wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>This trail is captured by a large array of sensitive photodetectors that are mounted up to three kilometres deep into the ice. With this information, IceCube can detect high energy neutrinos, measure their energy and determine where they came from. Other cosmic particles only travel a few kilometres through the Earth, at most. So, if the particle is seen to come up from below, it must have been produced by a neutrino interaction, as it is the only particle that can travel such a large distance through the planet.</p>
<p>The neutrino that was observed by IceCube in September 2017 is very special. This neutrino must have had an extremely high energy – IceCube scientists estimate between 183 and 290 trillion electron volts (a unit of energy). That is 28-45 times more energy than the particles in the beam of the <a href="https://theconversation.com/explainer-how-does-an-experiment-at-the-large-hadron-collider-work-42846">Large Hadron Collider </a> at CERN, the world’s most powerful particle accelerator. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/227380/original/file-20180712-27012-1m957qz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/227380/original/file-20180712-27012-1m957qz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/227380/original/file-20180712-27012-1m957qz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/227380/original/file-20180712-27012-1m957qz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/227380/original/file-20180712-27012-1m957qz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/227380/original/file-20180712-27012-1m957qz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/227380/original/file-20180712-27012-1m957qz.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">Sensors below the ice detected the neutrino, which was registered by computers in the IceCube building.</span>
<span class="attribution"><span class="source">IceCube/NSF</span></span>
</figcaption>
</figure>
<p>However, neutrinos with even higher energies have been observed by IceCube before. The exciting thing about the new discovery is that it has been shown to come from a blazar, which has been observed by other experiments, such as the <a href="https://www-glast.stanford.edu/instrument.html">FermiLAT satellite</a> and the <a href="https://magic.mpp.mpg.de/">MAGIC telescope</a>. In a <a href="https://www.youtube.com/watch?time_continue=2&v=DK9TMnC7n8E">blazar</a>, it is thought that the supermassive black hole at the centre absorbs matter to produce two extremely powerful jets of radiation. These jets could act as powerful particle accelerators. </p>
<p>Blazars were long suspected as a possible source of very high energy neutrinos in the universe, but we now have firm evidence. Together with IceCube, observations of this blazar have been made using telescopes that are sensitive to different types of electromagnetic radiation: radio, optical, gamma ray, and X-ray. </p>
<p>With this observation, IceCube has made a significant step forward in neutrino astronomy. Its neutrino adds new information to the observation of the blazar, helping us to understand these fascinating objects better. It can tell us about the mechanism of particle acceleration in blazars and more about how blazars produce such tremendous amounts of energy. We may even learn something new about the universe, or neutrinos, that we didn’t expect.</p><img src="https://counter.theconversation.com/content/99785/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Peeters 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 giant detector at the South Pole has observed a neutrino from a black hole in a distant galaxy for the first time.Simon Peeters, Reader (Physics and Astronomy), University of SussexLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/984812018-06-21T18:05:17Z2018-06-21T18:05:17ZHow we proved Einstein right on a galactic scale – and what it means for dark energy and dark matter<figure><img src="https://images.theconversation.com/files/224077/original/file-20180620-137717-wwwnon.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When galaxies align.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>Gravity may be the weakest of the <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/funfor.html">fundamental forces</a> in nature, but it is ultimately what enabled life on Earth to evolve. Thanks to its weak attractiveness over long distances, mass in the early universe could clump together and form galaxies, stars and planets such as our own.</p>
<p>Our working theory for gravity comes from <a href="https://theconversation.com/how-einsteins-general-theory-of-relativity-killed-off-common-sense-physics-50042">Albert Einstein’s general theory of relativity</a>, which states that gravity is a consequence of massive objects warping the very fabric of spacetime. Scientists have validated the theory with great precision in our solar system, but we haven’t been able to do the same on larger distances – until now. </p>
<p>Our new study, <a href="http://science.sciencemag.org/cgi/doi/10.1126/science.aao2469">published in Science</a>, shows that general relativity also holds true on the scale of entire galaxies. The findings strengthen the popular view in cosmology that 95% of the universe is made up of invisible substances dubbed <a href="https://theconversation.com/from-machos-to-wimps-meet-the-top-five-candidates-for-dark-matter-51516">dark matter</a> and <a href="https://theconversation.com/the-experiments-trying-to-crack-physics-biggest-question-what-is-dark-energy-52917">dark energy</a> – ruling out several competing theories.</p>
<p>The first ever test of general relativity was carried out by <a href="https://www.wired.com/2009/05/dayintech-0529/">Arthur Eddington in 1919</a>. As massive objects bend spacetime, light rays should be deflected as they pass the object rather than travelling in a straight line. Eddington managed to show that this was the case for light bending around the sun during a solar eclipse. Perhaps surprisingly, it has taken exactly 99 years for us to do the same for an entire galaxy.</p>
<h2>Cosmic alignment</h2>
<p>The galaxy we investigated has the catchy name <a href="https://www.spacetelescope.org/images/opo0708b/">ESO 325-G004</a> – let’s call it E325. Located some 450m light years away, it is one of the closest examples of a rare cosmic alignment – sitting directly between us and a second, more distant, galaxy. The background galaxy in this case is some 17 billion light years further behind. The centres of these two galaxies are aligned to better than one ten-thousandth of a degree. </p>
<p>Because light rays from the distant galaxy are deflected as they travel through the curved spacetime around E325, we see images of it that are slightly distorted from what we would otherwise see – an effect 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>. It’s a bit like looking at an object through the stem of a wine glass. The deflection of light passing E325 is about 1/1200 of a degree. </p>
<p>If the curvature of spacetime near the first galaxy is great enough – and in the case of E325 it is – then multiple images of the background galaxy will form on either side of the lens galaxy when looking at it with a telescope. The image below shows this effect as we observed it with the <a href="https://theconversation.com/telescopes-on-the-ground-may-be-cheaper-but-hubble-shows-why-they-are-not-enough-40724">Hubble Space Telescope</a>. The size of this so-called “Einstein ring” tells us how much spatial curvature there is around E325 – more curvature means a bigger ring.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/224079/original/file-20180620-137714-14624ca.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/224079/original/file-20180620-137714-14624ca.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/224079/original/file-20180620-137714-14624ca.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/224079/original/file-20180620-137714-14624ca.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/224079/original/file-20180620-137714-14624ca.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/224079/original/file-20180620-137714-14624ca.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/224079/original/file-20180620-137714-14624ca.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">
<figcaption>
<span class="caption">The gravitational lens ESO325-G004. After subtracting the light of the galaxy, a blue Einstein ring becomes visible in the centre.</span>
<span class="attribution"><span class="source">NASA/Hubble</span></span>
</figcaption>
</figure>
<p>We also measured the amount of mass in E325 by looking at how fast the stars are moving in the galaxy. Similar to the Earth orbiting the sun, the stars in E325 orbit around the galaxy’s centre of mass, with gravity holding them in their trajectories. More mass in the galaxy means a stronger gravitational force and so the stars orbit faster. </p>
<p>To measure their speed, we used the “<a href="https://theconversation.com/explainer-the-doppler-effect-7475">Doppler effect</a>” – the stretching or squashing of waves because of motion. A radar speed camera makes use of it by detecting the change in the radio frequency from signals bounced off cars to measure their speed. In a similar way, we measured the change in frequency in the light from stars to estimate their speed. The light from stars moving towards us is slightly shifted to the blue (a specific frequency), and stars moving away are shifted to the red. The faster they move, the bigger the shift.</p>
<p>Because E325 is so distant, it’s not possible to measure the Doppler effect for individual stars. We instead measured the light from all the stars in a patch and estimated the different velocities using statistical methods. These observations were made using the <a href="http://www.eso.org/public/unitedkingdom/teles-instr/paranal-observatory/vlt/">Very Large Telescope</a> in Chile.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/224180/original/file-20180621-137725-87czkm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/224180/original/file-20180621-137725-87czkm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/224180/original/file-20180621-137725-87czkm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/224180/original/file-20180621-137725-87czkm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/224180/original/file-20180621-137725-87czkm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/224180/original/file-20180621-137725-87czkm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/224180/original/file-20180621-137725-87czkm.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">Moonset over the Very Large Telescope.</span>
<span class="attribution"><span class="source">G.Gillet/ESO</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Once we had measured the velocities of the stars and the radius of the “Einstein ring”, we combined the two results to see if the amount of spatial curvature was consistent with the total mass of the galaxy. We found that it was, with a mere 9% total uncertainty. This is the most precise test of general relativity over length scales larger than the solar system. Although scientists have made similar measurements previously, they have never managed to achieve the precision we did.</p>
<h2>Dark energy and matter</h2>
<p>But why should we care so much about whether Einstein was right or wrong? There’s actually a lot at stake – much of our cosmological understanding comes from interpretation of observations of the universe that depend on general relativity being correct. If general relativity didn’t hold up, cosmology would truly be in crisis.</p>
<p>According to most cosmologists, the vast majority of our universe is made up of dark matter and dark energy. Dark matter is needed to explain the observed motions of stars in galaxies. While we can’t see it directly, we can see that it has a gravitational pull on stars. Meanwhile, dark energy – which exerts an expansive force on the universe – is needed to explain the fact that the expansion of the universe is speeding up. </p>
<p>But there are <a href="https://theconversation.com/new-theory-of-general-relativity-casts-doubt-on-dark-matter-16446">alternative theories of gravity</a> that can explain away these mysterious substances. They typically tweak how gravity works over long distances so that dark energy isn’t needed to explain the observations. </p>
<p>But our result poses a problem for these alternative theories by showing that gravity does behave the way general relativity expects on scales of up to 6,000 light years. Not only does our study therefore validate Einstein, it also shows that either dark energy and dark matter are real (whatever they are), or general relativity needs to be amended only on length scales that are larger than galaxies. </p>
<p>In the next decade, two new telescopes – the <a href="http://sci.esa.int/euclid/?secured=-1">Euclid satellite</a> and the <a href="https://www.lsst.org/">Large Synoptic Survey Telescope</a> – will be able to detect deviations from general relativity on scales more than 1,000 times longer than probed in E325. If general relativity also passes these tests we will know it is the right theory to describe gravity’s effects on the universe as a whole. So far, it is looking good for Einstein.</p><img src="https://counter.theconversation.com/content/98481/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Collett receives funding from the University of Portsmouth.</span></em></p>Exactly 99 years after Einstein’s theory of general relativity was proven right in our own solar system, scientists show that it also holds true for entire galaxies.Thomas Collett, Research Fellow in Astrophysics, University of PortsmouthLicensed 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/952802018-05-14T10:38:19Z2018-05-14T10:38:19ZThe next big discovery in astronomy? Scientists probably found it years ago – but they don’t know it yet<figure><img src="https://images.theconversation.com/files/217776/original/file-20180504-166887-8ht3tz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's illustration of a black hole "eating" a star.</span> <span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA20027">NASA/JPL-Caltech</a></span></figcaption></figure><p>Earlier this year, astronomers stumbled upon a fascinating finding: <a href="https://www.nature.com/articles/nature25029#main">Thousands of black holes likely exist</a> near the center of our galaxy. </p>
<p>The X-ray images that enabled this discovery <a href="http://chandra.harvard.edu/">weren’t from some state-of-the-art new telescope</a>. Nor were they even recently taken – some of the data was collected nearly 20 years ago. </p>
<p>No, the researchers discovered the black holes by digging through old, long-archived data. </p>
<p>Discoveries like this will only become more common, as the era of “big data” changes how science is done. Astronomers are gathering an exponentially greater amount of data every day – so much that it will take years to uncover all the hidden signals buried in the archives. </p>
<h2>The evolution of astronomy</h2>
<p>Sixty years ago, the typical astronomer worked largely alone or in a small team. They likely had access to a respectably large ground-based optical telescope at their home institution. </p>
<p>Their observations were largely confined to optical wavelengths – more or less what the eye can see. That meant they missed signals from a host of astrophysical sources, which can emit non-visible radiation from <a href="https://astrobites.org/guides/astronomy-the-electromagnetic-spectrum/">very low-frequency radio all the way up to high-energy gamma rays</a>. For the most part, if you wanted to do astronomy, you had to be an <a href="https://books.google.com/books/about/Edwin_Hubble.html?id=ts5-CrkyJnIC">academic or eccentric rich person</a> with access to a good telescope.</p>
<p>Old data was stored in the form of photographic plates or published catalogs. But accessing archives from other observatories could be difficult – and it was virtually impossible for amateur astronomers. </p>
<p>Today, there are observatories that cover the <a href="https://science.nasa.gov/ems/01_intro">entire electromagnetic spectrum</a>. No longer operated by single institutions, these state-of-the-art observatories are usually launched by space agencies and are often <a href="http://www.almaobservatory.org/en/about-alma-at-first-glance/global-collaboration/">joint efforts involving many countries</a>. </p>
<p>With the coming of the digital age, almost all data are publicly available shortly after they are obtained. This makes astronomy very democratic – anyone who wants to can reanalyze almost any data set that makes the news. (You too can look at the Chandra data that led to the discovery of thousands of black holes!) </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/217993/original/file-20180507-46338-au8brc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/217993/original/file-20180507-46338-au8brc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/217993/original/file-20180507-46338-au8brc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=462&fit=crop&dpr=1 600w, https://images.theconversation.com/files/217993/original/file-20180507-46338-au8brc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=462&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/217993/original/file-20180507-46338-au8brc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=462&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/217993/original/file-20180507-46338-au8brc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=581&fit=crop&dpr=1 754w, https://images.theconversation.com/files/217993/original/file-20180507-46338-au8brc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=581&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/217993/original/file-20180507-46338-au8brc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=581&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.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/centers/marshall/history/this-week-in-nasa-history-hubble-space-telescope-deployed-april-25-1990.html">NASA</a></span>
</figcaption>
</figure>
<p>These observatories generate a staggering amount of data. For example, the Hubble Space Telescope, operating since 1990, has made over <a href="https://www.nasa.gov/mission_pages/hubble/story/index.html">1.3 million observations</a> and transmits around 20 GB of raw data every week, which is impressive for a telescope first designed in the 1970s. The <a href="http://www.almaobservatory.org/en/home/">Atacama Large Millimeter Array</a> in Chile now anticipates adding <a href="https://science.nrao.edu/facilities/alma/naasc-memo-series/naasc-memos/110.naasc-data-rates">2 TB of data</a> to its archives every day.</p>
<h2>Data firehose</h2>
<p>The archives of astronomical data are already impressively large. But things are about to explode. </p>
<p>Each generation of observatories are usually at least <a href="http://ecuip.lib.uchicago.edu/multiwavelength-astronomy/infrared/tools/15.html">10 times more sensitive than the previous</a>, either because of improved technology or because the mission is simply larger. Depending on how long a new mission runs, it can detect hundreds of times more astronomical sources than previous missions at that wavelength. </p>
<p>For example, compare the early EGRET gamma ray observatory, which flew in the 1990s, to NASA’s flagship mission Fermi, which turns 10 this year. <a href="https://arxiv.org/abs/0806.0113">EGRET detected only about 190 gamma ray sources</a> in the sky. Fermi has seen <a href="https://fermi.gsfc.nasa.gov/ssc/data/access/lat/fl8y/">over 5,000</a>. </p>
<p>The Large Synoptic Survey Telescope, an optical telescope <a href="https://www.lsst.org/gallery/collection/construction-update-4">currently under construction in Chile</a>, will image the entire sky every few nights. It will be so sensitive that it will <a href="https://www.lsst.org/scientists/keynumbers">generate 10 million alerts per night</a> on new or transient sources, leading to a catalog of over 15 petabytes after 10 years.</p>
<p>The Square Kilometre Array, when completed in 2020, will be the most sensitive telescope in the world, capable of <a href="https://www.astrobio.net/alien-life/seti-on-the-ska/">detecting airport radar stations</a> of alien civilizations up to 50 light-years away. In just one year of activity, it will <a href="https://www.computerworld.com.au/article/392735/ska_telescope_generate_more_data_than_entire_internet_2020/">generate more data than the entire internet</a>.</p>
<p>These ambitious projects will test scientists’ ability to handle data. Images will need to be automatically processed – meaning that the data will need to be reduced down to a manageable size or transformed into a finished product. The new observatories are pushing the envelope of computational power, requiring facilities capable of processing <a href="https://www.lsst.org/about/dm/technology">hundreds of terabytes per day</a>. </p>
<p>The resulting archives – all publicly searchable – will contain 1 million times more information that what can be stored on your typical 1 TB backup disk.</p>
<h2>Unlocking new science</h2>
<p>The data deluge will make astronomy become a more collaborative and open science than ever before. Thanks to internet archives, <a href="https://photographingspace.com/download-hubble-data/">robust learning communities</a> and <a href="https://www.zooniverse.org/projects/zookeeper/galaxy-zoo/">new outreach initiatives</a>, citizens can now participate in science. For example, with the computer program <a href="https://einsteinathome.org/">Einstein@Home</a>, anyone can use their computer’s idle time to help search for rapidly-rotating neutron stars. </p>
<p>It’s an exciting time for scientists, too. Astronomers like myself often study physical phenomena on timescales so wildly beyond the typical human lifetime that watching them in real-time just isn’t going to happen. Events like a typical galaxy merger – <a href="https://phys.org/news/2017-10-image-hubble-captures-collision-galaxies.html">which is exactly what it sounds like</a> – can take hundreds of millions of years. All we can capture is a snapshot, like a single still frame from a video of a car accident. </p>
<p>However, there are some phenomena that occur on shorter timescales, taking just a few decades, years <a href="http://iopscience.iop.org/article/10.1088/0034-4885/69/8/R01/meta">or even seconds</a>. That’s how scientists discovered those thousands of black holes in the new study. It’s also how they <a href="http://iopscience.iop.org/article/10.1088/2041-8205/792/2/L29/meta">recently realized</a> that the X-ray emission from the center of a nearby dwarf galaxy has been fading since first detected in the 1990s. These new discoveries suggest that more will be found in archival data spanning decades. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/218114/original/file-20180508-184630-13uu4fd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/218114/original/file-20180508-184630-13uu4fd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/218114/original/file-20180508-184630-13uu4fd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/218114/original/file-20180508-184630-13uu4fd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/218114/original/file-20180508-184630-13uu4fd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/218114/original/file-20180508-184630-13uu4fd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/218114/original/file-20180508-184630-13uu4fd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/218114/original/file-20180508-184630-13uu4fd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&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 black-hole-powered jet of hot gas in the giant elliptical galaxy M87.</span>
<span class="attribution"><a class="source" href="http://hubblesite.org/image/3228/news_release/2013-32">NASA, ESA, E. Meyer, W. Sparks, J. Biretta, J. Anderson, S.T. Sohn, and R. van der Marel (STScI), C. Norman (Johns Hopkins University), and M. Nakamura (Academia Sinica)</a></span>
</figcaption>
</figure>
<p>In my own work, I use Hubble archives to make <a href="http://hubblesite.org/news_release/news/2015-19">movies of “jets,”</a> high-speed plasma ejected in beams from black holes. I used over 400 raw images spanning 13 years to make a <a href="http://hubblesite.org/news_release/news/2013-32">movie of the jet in nearby galaxy M87</a>. That movie showed, for the first time, the twisting motions of the plasma, suggesting that the jet has a helical structure. </p>
<p>This kind of work was only possible because other observers, for other purposes, just happened to capture images of the source I was interested in, back when I was in kindergarten. As astronomical images become larger, higher resolution and ever more sensitive, this kind of research will become the norm.</p>
<p><em>This article has been updated to correct what Einstein@Home searches for.</em></p><img src="https://counter.theconversation.com/content/95280/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Eileen Meyer receives funding from NASA and the National Science Foundation. </span></em></p>Astronomers are gathering an exponentially greater amount of data every day – so much that it will take years to uncover all the hidden signals buried in the archives.Eileen Meyer, Assistant Professor of Physics, University of Maryland, Baltimore CountyLicensed 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/795762018-02-19T18:47:30Z2018-02-19T18:47:30ZSizes matters for black hole formation, but there’s something missing in the middle ground<figure><img src="https://images.theconversation.com/files/206898/original/file-20180219-75990-oiivgr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of a supermassive black hole at the centre of a galaxy.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/jpl/nustar/pia18919">NASA/JPL-Caltech</a></span></figcaption></figure><p>So far, all <a href="http://astronomy.swin.edu.au/cosmos/B/Black+Hole">black holes</a> discovered by astronomers fall into two broad categories: “stellar mass” black holes and “supermassive” black holes.</p>
<p>But what puzzles astronomers is why the two extremes – what about intermediate-sized black holes?</p>
<p>Black holes were predicted by Albert Einstein’s general theory of relativity. Their gravity is so strong that no material object, not even light, can escape from their vicinity. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/something-big-exploded-in-a-galaxy-far-far-away-what-was-it-74372">Something big exploded in a galaxy far, far away: what was it?</a>
</strong>
</em>
</p>
<hr>
<p>Astronomers have only been able to obtain evidence for their existence in recent decades by studying black holes accreting (attracting) gas from nearby stars and finding fast-moving stars in the vicinity of black holes. </p>
<p>But since 2015 an exciting third way to detect black holes has become available: gravitational waves from merging black holes.</p>
<h2>From one extreme…</h2>
<p><a href="http://astronomy.swin.edu.au/cosmos/S/Stellar+Black+Hole">Stellar mass black holes</a> can have masses between a few to a few tens of solar masses – the mass of our Sun. They are thought to form at the end of the lives of massive stars. When these stars run out of gas from which to produce energy, they leave behind massive remnants that can only collapse into black holes. </p>
<p>So far, astronomers have discovered a dozen stellar mass black hole candidates in the Milky Way, most of which accrete matter from nearby companion stars. </p>
<p>They also detected gravitational waves from several merging stellar mass black hole pairs in distant galaxies. </p>
<p>It’s <a href="https://news.uci.edu/2017/08/07/uci-celestial-census-indicates-that-black-holes-pervade-the-universe/">estimated that our Milky Way alone</a> should contain about 100 million stellar mass black holes, most of which do not have close companions from which they can accrete matter, and which therefore stay invisible.</p>
<h2>… to the other</h2>
<p>At the other end of the mass scale are what astronomers call <a href="http://astronomy.swin.edu.au/cosmos/S/Supermassive+Black+Hole">supermassive black holes</a>. These are about a million to a few billion times more massive than our Sun.</p>
<p>Astronomers think that almost every large galaxy <a href="https://www.sciencealert.com/supermassive-black-hole-mass-galactic-star-formation">contains a supermassive black hole at its centre</a>.</p>
<p>The Milky Way, for example, contains a black hole of about 4 million solar masses, called <a href="https://www.nasa.gov/mission_pages/chandra/multimedia/black-hole-SagittariusA.html">Sagittarius A*</a> (Sgr A*), in its centre. Astronomers can study this black hole by looking at the motion of stars that are close to Sgr A* and are flung through space by the huge gravitational attraction of the black hole. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/sls28MTNFm0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Is that a supermassive black hole?</span></figcaption>
</figure>
<p>Although astronomers have gained a good understanding of the distribution and masses of supermassive black holes in galaxies in the nearby universe, they still do not know where supermassive black holes come from.</p>
<p>Observations show that some supermassive black holes already existed and were actively accreting gas from their surroundings when the universe was just a few hundred million years old.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/206895/original/file-20180219-75990-1ethgpm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/206895/original/file-20180219-75990-1ethgpm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/206895/original/file-20180219-75990-1ethgpm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=433&fit=crop&dpr=1 600w, https://images.theconversation.com/files/206895/original/file-20180219-75990-1ethgpm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=433&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/206895/original/file-20180219-75990-1ethgpm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=433&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/206895/original/file-20180219-75990-1ethgpm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=545&fit=crop&dpr=1 754w, https://images.theconversation.com/files/206895/original/file-20180219-75990-1ethgpm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=545&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/206895/original/file-20180219-75990-1ethgpm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=545&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 composite x-ray and infrared image of the supermassive black hole Sagittarius A* at the centre of the Milky Way.</span>
<span class="attribution"><a class="source" href="http://www.chandra.harvard.edu/photo/2013/sgra_gas/">NASA/UMass/D.Wang et al., IR: NASA/STScI</a></span>
</figcaption>
</figure>
<p>In 2011 a team of astronomers said they had <a href="https://www.eso.org/public/news/eso1122/">found evidence</a> of a supermassive black hole that existed only 770 million years after the Big Bang. Then, last month, another team of <a href="https://www.space.com/39000-oldest-farthest-monster-black-hole-yet.html">astronomers revealed</a> what they think could be evidence of a supermassive black hole from when the universe was only 690 million years old.</p>
<p>This creates a problem for theories that assume that supermassive black holes grew out of the stellar-mass black holes left behind by the first generation of stars in the early universe.</p>
<p>There is not enough time for these black holes to have grown to reach the huge masses that we can see in observations of the first galaxies.</p>
<h2>The middle ground for black holes</h2>
<p>An alternative theory is that supermassive black holes form from so-called intermediate-mass black holes. These hypothetical black holes could have masses from a few hundred to a few hundred thousand solar masses. </p>
<p>Starting more massive, supermassive black holes would need less time to grow to their present sizes. They could also accrete mass more efficiently since the maximum amount of mass that a black hole can accrete is directly proportional to its size.</p>
<p>Intermediate mass black holes could form out of the collapse of <a href="http://www.sciencemag.org/news/2015/06/astronomers-spot-first-generation-stars-made-big-bang">very massive stars</a> that might have existed in the very early universe.</p>
<p>Nowadays stars form with an upper mass limit of at most a <a href="http://iopscience.iop.org/article/10.1088/1361-6552/aa70d5/meta">few 100 solar masses</a>. Conditions in the very early universe might have been more favourable towards building more massive stars and might have allowed the formation of stars of a few thousand or maybe even up to a million times the mass of our sun. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/206897/original/file-20180219-75961-p6m81x.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/206897/original/file-20180219-75961-p6m81x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/206897/original/file-20180219-75961-p6m81x.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=333&fit=crop&dpr=1 600w, https://images.theconversation.com/files/206897/original/file-20180219-75961-p6m81x.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=333&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/206897/original/file-20180219-75961-p6m81x.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=333&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/206897/original/file-20180219-75961-p6m81x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=419&fit=crop&dpr=1 754w, https://images.theconversation.com/files/206897/original/file-20180219-75961-p6m81x.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=419&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/206897/original/file-20180219-75961-p6m81x.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=419&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 chart illustrates the relative masses of stellar black holes and supermassive black holes, and the mystery of the intermediate-mass black holes, with masses up to more than 100,000 times that of our sun, remains unsolved.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/jpl/nustar/pia18842">NASA/JPL-Caltech (edited)</a></span>
</figcaption>
</figure>
<h2>The hunt is on</h2>
<p>Astronomers are currently searching for intermediate mass black holes and there are <a href="http://www.skyandtelescope.com/astronomy-news/new-candidates-for-midsize-black-holes/">a few potential candidates</a>. Like their more massive cousins they could reveal their existence by accreting material from nearby stars or by the fast motion of nearby stars. </p>
<p>A prime place to look for intermediate mass black holes could be globular clusters, dense clusters of a few hundred thousand of stars to a few million of stars. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/black-holes-are-even-stranger-than-you-can-imagine-72743">Black holes are even stranger than you can imagine</a>
</strong>
</em>
</p>
<hr>
<p>Like supermassive black holes, globular clusters are old and are among the first objects which have formed in the universe. </p>
<p>Astronomers – including at the University of Queensland – recently <a href="https://www.uq.edu.au/news/article/2017/02/astronomers-find-evidence-of-missing-link%E2%80%99-black-hole">found evidence</a> that such an intermediate mass black hole with about 2,200 times the mass of our Sun could exist at the centre of the globular cluster 47 Tucanae.</p>
<p>They did this by studying the acceleration of pulsars (compact remnants of dead stars that formed with about 20 times the mass of our Sun) in the globular cluster.</p>
<p>If more of these can be found, they might provide the missing link between stellar mass and supermassive black holes and could shed light on how supermassive black holes have formed.</p><img src="https://counter.theconversation.com/content/79576/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Holger Baumgardt received funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Michael Drinkwater receives funding from Astronomy Australia Limited and the Australian Research Council.</span></em></p>Black holes may come in many sizes, but there’s still a gap in the middle. The hunt is on to solve the mystery of where are the intermediate size black holes.Holger Baumgardt, Associate Professor, The University of QueenslandMichael Drinkwater, Professor of Astrophysics, The University of QueenslandLicensed 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/846702017-10-05T21:56:57Z2017-10-05T21:56:57ZStar Trek discovery of alien life veers away from likely reality<figure><img src="https://images.theconversation.com/files/189053/original/file-20171005-9753-itcvsp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Here, an alien crew member, Saru on Star Trek: Discovery. We often rely on science fiction to guide our expectations of alien life. We can hope lessons about accepting beings very different from yourself can be extracted by the series end. </span> <span class="attribution"><span class="source">(Courtesy of CBS Studios)</span></span></figcaption></figure><p>Imagine yourself on the USS Enterprise. Your captain (James Kirk, Jean-Luc Picard, Kathryn Janeway… take your pick!) asks you to scan a nearby planet: Could it harbour life? </p>
<p>You go down your checklist: Oxygen, liquid water, land mass, food. These are the markers science fiction and much of science has looked for during our search for alien life, but is it accurate? </p>
<p>The perfect environment in which life can thrive may not be as simple as we initially thought. And it may not look anything like our own Earth.</p>
<p>To figure out where to look for life, we can start at large scales. Just like animals, <a href="https://www.space.com/22437-main-sequence-stars.html">stars change</a> over their lifetimes. The stability and age of any given star can give us a clue into how likely it may have a planet with life in its system. Very bright, blue stars that tend to populate spiral galaxies will usually only last a few hundreds of millions of years. </p>
<p>In contrast, smaller, dimmer red stars that are common in elliptical galaxies can last for tens of billions of years. The rule is simple: The more massive a star, the shorter and more turbulent its life tends to be. And life will have a hard go at it if the system’s star goes <a href="https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-supernova.html">supernova</a> before anything can even get started.</p>
<h2>Habitable planets</h2>
<p>If we look at our own story nestled in our little solar neighbourhood, the very first humans (by the broadest definition of the term) didn’t appear until a few million years ago. </p>
<p>If we follow Star Trek’s date of 2063 for <a href="http://memory-alpha.wikia.com/wiki/Star_Trek:_First_Contact">first contact</a> with another alien race, the Vulcans, that’s basically 4.5 billion years between the creation of our solar system and making our first alien friends. It took the very simplest forms of life nearly 750 million years before appearing on Earth. Luckily for us, our quite averagely sized Sun has a lifespan of about 10 billion years. This gave complex life ample time to develop.</p>
<p>In February 2017, NASA made an incredible announcement. They had detected a system 39 light years away with seven exoplanets: TRAPPIST-1. Three of the planets were in the “Goldilocks zone.” This zone covers the region where liquid water can exist, and depends on the size and temperature of the parent star. </p>
<p>All seven planets orbit a type of star called an ultra-cool dwarf, about 1/13th the size of our Sun. These types of stars can live a relatively stable life for hundreds of billions of years. Simulations of planet formation have also shown that their small size and low temperatures make them more likely to host Earth-like planets. </p>
<p>Dedicated telescopes such as the Kepler Telescope and the upcoming James Webb Space Telescope are building an impressive catalogue of thousands of these exoplanets. Surely, we’re bound to find something out there with alien life! But what if we didn’t have to look so far?</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/187670/original/file-20170926-22303-e9z9ta.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/187670/original/file-20170926-22303-e9z9ta.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/187670/original/file-20170926-22303-e9z9ta.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/187670/original/file-20170926-22303-e9z9ta.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/187670/original/file-20170926-22303-e9z9ta.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=466&fit=crop&dpr=1 754w, https://images.theconversation.com/files/187670/original/file-20170926-22303-e9z9ta.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=466&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/187670/original/file-20170926-22303-e9z9ta.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=466&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Cassini image showcasing Enceladus’ plumes of ice water. Molecular hydrogen was detected within these plumes by the probe’s specialized instruments.</span>
<span class="attribution"><span class="source">NASA/JPL/STScI</span></span>
</figcaption>
</figure>
<h2>Life in our solar neighbourhood?</h2>
<p>NASA made another incredible announcement only two months after the TRAPPIST-1 news. The Cassini spacecraft had detected a possible chemical food source for alien life in the form of molecular hydrogen on Saturn’s sixth moon, Enceladus — the energy equivalent of 300 pizzas per hour, no less! </p>
<p>The future exploration of Enceladus and other “Ocean Worlds” such as Jupiter’s moon, Europa, and Saturn’s largest moon, Titan, is currently the most promising prospect of finding alien life in our own solar system. But our first forays onto these worlds have shown us landscapes very unlike Earth’s: oceans of methane, surfaces entirely covered in cracked ice, endless underground oceans with no land masses in sight. This puts into question our previously determined list of “must-haves” to find alien life.</p>
<p>That being said, life forms on our very own home planet continue to surprise us by their resilience, robustness and alien-like qualities. We are always discovering new organisms that thrive in extreme conditions we would have otherwise thought completely deadly. </p>
<p>In 2010, NASA made a breakthrough discovery. An “Arsenic Bug” microorganism was found feeding off the toxic arsenic in Mono Lake, Calif. These incredibly sturdy organisms known as <a href="https://oceanservice.noaa.gov/facts/extremophile.html">extremophiles</a> may even tie back to the very origins of life on Earth.</p>
<h2>Unusual life</h2>
<p>In 1977, scientists made a stunning discovery at the bottom of the Pacific Ocean. Hydrothermal vents were heating the frigid deep sea waters and ejecting impressive amounts of chemicals into their surroundings. These dissolved chemicals provide the necessary energy to support bacteria that form the base of the food chain of an impressively diverse underwater ecosystem. </p>
<p>Scientists now suggest that ancient hydrothermal vents found on Earth billions of years ago may have populated our world with its very first blips of life. This ecosystem may be very similar to the one hidden at the bottom of Enceladus’ oceans! These revelations have expanded our very definition of life. If we are to detect life elsewhere in the universe, it’s clear we must cast a wide net. </p>
<p>As we continue our tireless search for someone or something out there in the great dark void, we need to stop and ask ourselves: “What are we even looking for?” A survey of the general population will show that we often rely on pieces of science fiction such as <em>Star Trek</em> to guide our expectations of alien life. </p>
<p>The great majority of these works portray aliens as humanoid beings. This makes for compelling story-telling; can you imagine Capt. Jean-Luc Picard having an intellectual showdown with a colony of bacteria? Perhaps not as interesting as discoursing with an intelligent bipedal reptilian creature who happens to speak English. Using a universal translator helps, I’m sure.</p>
<h2>Evolution</h2>
<p>But even <em>Star Trek</em> has been keeping up with the times. The best example of this is the portrayal of Klingons over the years. When they first appeared in the original series, they were merely people with disconcerting tans and facial hair.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/189061/original/file-20171005-6575-14a8bt7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/189061/original/file-20171005-6575-14a8bt7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/189061/original/file-20171005-6575-14a8bt7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/189061/original/file-20171005-6575-14a8bt7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/189061/original/file-20171005-6575-14a8bt7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/189061/original/file-20171005-6575-14a8bt7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/189061/original/file-20171005-6575-14a8bt7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/189061/original/file-20171005-6575-14a8bt7.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">Klingon in <em>Star Trek: Discovery</em>.</span>
<span class="attribution"><span class="source">(Handout)</span></span>
</figcaption>
</figure>
<p>As they evolved through <em>The Next Generation</em> and beyond, they gained facial ridges to differentiate them from humans. This came with a very rich culture and language, but not unlike some found throughout human history (the Vikings come to mind). </p>
<p>In the newly released <em>Star Trek: Discovery</em>, you will be hard-pressed to find Lt. Commander Worf’s face in the Klingons’ much more alien appearance. While this may solidify their role as the Federation’s main antagonists for now, we can hope a lesson about accepting beings very different from yourself can be extracted by the series’ end. As special effects have improved, so too have our idea of what alien life could look like.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"886987911270473736"}"></div></p>
<p>If we consider the variety of planets and moons we’ve discovered that could harbour life, we realize that “habitable” does not need to mean Earth-like. Thus, how can we expect life to evolve exactly as it did on Earth when these alien landscapes are so different from our own? </p>
<p>The theory of evolution has showcased with what skill life manages to adapt itself to its surroundings. A more probable depiction of the Klingons could be intelligent octopus-like creatures that thrive on a purely aquatic world such as Enceladus. </p>
<p>Alien life may solely exist in the form of viruses with which communication would be impossible: Not exactly the kind of fodder <em>Star Trek</em> has historically fed off for plot. It may even take a form we have not yet obtained the capacity to imagine. At the end of it all, when we do finally reach the point of first contact, it may not be as simple as a Vulcan salute.</p><img src="https://counter.theconversation.com/content/84670/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nathalie Nguyen-Quoc Ouellette 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>Star Trek: Discovery explores our corner of the block – just a fraction of the galaxy. Some stars are better candidates for intelligent alien life, and it may not be anything like we imagine.Nathalie Nguyen-Quoc Ouellette, Astronomer | Education & Outreach Officer, Queen's University, OntarioLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/757742017-04-11T20:10:52Z2017-04-11T20:10:52ZLive fast, die young: a massive ‘dead red’ galaxy seen for the first time in the early Universe<figure><img src="https://images.theconversation.com/files/164770/original/image-20170411-31875-s8np91.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist’s impression of ZF-COSMOS-20115, a galaxy that stopped making new stars and rapidly turned into a compact red galaxy. </span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><p>The discovery of massive galaxy that stopped making any new stars by the time the Universe was only 1.65 billion years old means we may have to rethink our theories on how galaxies formed.</p>
<p>The galaxy, known as ZF-COSMOS-20115, formed all of its stars (more than three times as many as our Milky Way has today) through an extreme starburst event.</p>
<p>But it stopped forming stars to become a “red and dead” galaxy not much more than a billion years after the Big Bang. Such galaxies are common in our Universe today but not expected to have existed at this ancient epoch. Galaxies turn red when they stop forming stars due to the resulting absence of hot, blue stars that have very short lifetimes.</p>
<p>This discovery by <a href="http://zfire.swinburne.edu.au/team.html">our team</a> sets a new record for the earliest massive red galaxy, with details <a href="http://www.nature.com/nature/journal/v544/n7648/full/nature21680.html">published in Nature</a> this month.</p>
<p>It is an incredibly rare find that poses a new challenge to galaxy evolution models to accommodate the existence of such galaxies much earlier in the Universe.</p>
<h2>An earlier discovery</h2>
<p>To put this discovery in context, I’d like to give a short, personal history of research on early massive galaxies.</p>
<p>In 2004 I wrote an uncannily similar <a href="http://www.nature.com/nature/journal/v430/n6996/full/nature02667.html">Nature paper</a> about the existence of massive, old galaxies in the early Universe that were discovered in deep near-infrared surveys. At that time we were peering back across space to 3 billion years after the Big Bang. </p>
<p>These were a challenge for the models of <a href="https://astronomy.swin.edu.au/cosmos/G/Galaxy+Formation">galaxy formation</a> that scientists were working with at the time, the start of a period where our pictures of how galaxies formed were rapidly being rewritten. </p>
<p>At the time, a picture of galaxies forming by lots of <a href="http://astronomy.swin.edu.au/cosmos/H/Hierarchical+Clustering">mergers in hierarchical assembly</a> was in vogue. The problem was that this meant that today’s massive galaxies were in little bits billions of years ago. </p>
<p>But significant changes were made – driven in part by observations of the abundance of early massive galaxies, the observations of large gas-rich disk galaxies at these epochs and the discovery of “red nuggets” – extremely compact massive elliptical galaxies which stopped forming stars early on. </p>
<p>We moved to a picture where most galaxy growth and formation was driven by the formation of stars within the galaxy itself, from cosmic gas coming in to the galaxy. </p>
<p>This gas is fed into galaxies along the cosmic web by cold streams that are effective early on and allow us to grow massive galaxies more quickly in the computer modelling.</p>
<p>Many, many astronomers contributed to these developments and it was fun to play a minor role.</p>
<h2>The new discovery</h2>
<p>So what about this new discovery? This stems from the <a href="http://zfourge.tamu.edu/">ZFOURGE</a> survey, a deep near-infrared imaging survey we have been conducting on the <a href="http://obs.carnegiescience.edu/Magellan">Magellan telescopes</a> in Chile, since 2010. </p>
<p>Back in 2013, one of our students, Caroline Straatman of Leiden University, <a href="http://dx.doi.org/10.1088/2041-8205/783/1/L14">discovered</a> a population of pale red dots in the ZFOURGE survey. </p>
<p>These dots were bright in the near-infrared but very faint in the 35 other wavelength bands we observed. This peak suggested the presence of roughly 500 million year old stars but at a huge cosmic redshift.</p>
<p>In the local Universe this peak appears in blue light, so the redshift points to a time around 1.5 billion years after the Big Bang. The light suggested that no young stars were present, and the near-infrared brightness suggested these were massive objects (10<sup>11</sup> solar masses).</p>
<p>To put this in context, our Milky Way has been growing continuously for 12 billion years but is 3-5 times less massive.</p>
<p>Even more remarkably, the galaxies looked like <a href="http://astronomy.swin.edu.au/cosmos/E/elliptical+galaxy">ellipticals</a> and were almost point sources, even with high-resolution Hubble Space Telescope observations. They were less than 5,000 light years across. Extremely dense red nuggets at an earlier time than anyone had suspected.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/164767/original/image-20170411-31911-tlw9pa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/164767/original/image-20170411-31911-tlw9pa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/164767/original/image-20170411-31911-tlw9pa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=597&fit=crop&dpr=1 600w, https://images.theconversation.com/files/164767/original/image-20170411-31911-tlw9pa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=597&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/164767/original/image-20170411-31911-tlw9pa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=597&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/164767/original/image-20170411-31911-tlw9pa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=750&fit=crop&dpr=1 754w, https://images.theconversation.com/files/164767/original/image-20170411-31911-tlw9pa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=750&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/164767/original/image-20170411-31911-tlw9pa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=750&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 is what ZF-COSMOS-20115 really looks like (compared to the artist’s impression, top) in a close-up view. Even with Hubble’s 0.2-arcsec spatial resolution the object appears barely resolved due to its extreme compactness.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Lines in the spectrum</h2>
<p>In 2012 a powerful new near-infrared spectrograph was commissioned on the <a href="http://www.keckobservatory.org/">W M Keck telescopes</a> in Hawaii. Last year we used it to get a two-night exposure on some of these objects. </p>
<p>We were amazed when we got a spectrum of the brightest (and most massive). They showed the distinct signature of <a href="http://astronomy.swin.edu.au/cosmos/B/Balmer+series">Balmer absorption lines</a> of stars around 500 million years old. Importantly there was no sign of current star-formation.</p>
<p>This galaxy was already massive and between 500 million and 1 billion years old.</p>
<p>It must have formed extremely fast, and then its star formation died quickly. This extreme behaviour could require significant rewriting of our pictures of galaxy formation in the first billion years of cosmic history. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/GNsM60JBa9I?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Why? Well, we think galaxies form in the centres of halos of cold dark matter. Dark matter particles is not made of ordinary atoms, and particle physicists are still trying to detect these in the laboratory.</p>
<p>These halos can form very early and act as seeds for galaxy formation giving it a kick start. Without dark matter it would be difficult to form any galaxy. </p>
<p>The problem is at this early time there are barely enough massive dark matter halos to accommodate such massive galaxies. As a consequence in simulated Universes we don’t find this population of non-star forming galaxies so early, nor do we find the massive ancestors with extreme star-formation rates a billion years earlier.</p>
<p>So, do we need two recipes for galaxy formation where some form extremely quickly and the rest take 12 billion years?</p>
<p>Time will tell. The history of this field has shown that the theoretical community has a very strong record of postdiction (as opposed to prediction), and I expect a slew of papers will turn up in the next few weeks to explain this object!</p>
<p>Teasing of theorists aside, galaxy formation is a very difficult field to work in; the astrophysics are complex and it is very much driven by new observations which is why it is so much fun to work in.</p>
<p>Meanwhile our groups are pursuing the quest for massive galaxies to even earlier times. We have designed new filters to identify these and hope to start a new survey using the <a href="https://www.gemini.edu">Gemini telescopes</a> this year. Theorists, get your predictions in now.</p><img src="https://counter.theconversation.com/content/75774/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Karl Glazebrook receives funding from the Australian Research Council. </span></em></p>The recipe book for galaxy formation may need to be rewritten after the discovery of a massive galaxy that stopped making new stars early in the Universe’s history.Karl Glazebrook, Director & Distinguished Professor, Centre for Astrophysics & Supercomputing, Swinburne University of TechnologyLicensed 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/743522017-03-15T18:03:16Z2017-03-15T18:03:16ZLack of ‘dark matter’ in early galaxies perplexes astronomers<figure><img src="https://images.theconversation.com/files/160933/original/image-20170315-5364-1j7op1g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Most modern spiral galaxies, such as NGC 1300, are thought to have loads of dark matter in their outer regions.</span> <span class="attribution"><span class="source">NASA, ESA, and The Hubble Heritage Team STScI/AURA)</span></span></figcaption></figure><p>It may seem like we’ve got the universe pretty much figured out. We have a relatively good idea about how it started and how it is evolving. We’ve sent probes to neighbouring planets, discovered an increasing number of exoplanets and are cataloguing the family tree of galaxies.</p>
<p>But there is some pretty basic stuff that we just don’t have a clue about – such as what the <a href="https://theconversation.com/the-search-for-dark-matter-and-dark-energy-just-got-interesting-46422">vast majority of the cosmos</a> is actually made of. For example, for all the matter we can see in the universe, there is at least five times more invisible material called “dark matter”. We know it is there because of the gravitational pull it has on surrounding matter. The matter we can see in a galaxy or galaxy cluster, such as stars, isn’t enough to hold it together by gravity alone, meaning some “dark” material must be lurking there, too. </p>
<p>So far, we have not been able to work out <a href="https://theconversation.com/from-machos-to-wimps-meet-the-top-five-candidates-for-dark-matter-51516">what this substance is</a> and where it came from. And now our new study, <a href="http://nature.com/articles/doi:10.1038/nature21685">published in Nature</a>, is making the matter even more confusing by suggesting that in early galaxies it was present only in tiny amounts.</p>
<h2>Galaxy puzzle</h2>
<p>Much of astronomy is the study of a battle against gravity. Stars shine so as not to succumb to gravitational collapse under their own weight. The Milky Way rotates as a means of supporting itself against gravity. Some more massive galaxies show less or no coherent rotation, but they feature random motions to balance gravity. This is why measuring the movement of galaxies is an efficient way to determine the amount of gravitational pull – or the total mass present within a certain area of space.</p>
<p>This year marked the <a href="https://www.theguardian.com/science/2016/dec/26/vera-rubin-pioneering-astronomer-dark-matter-died-aged-88">passing of one of the pioneers of galaxy dynamics</a>, Vera Rubin. She discovered that the outer regions of nearby spiral galaxies spin just as fast as the regions near the centre. This contributed greatly to our modern-day picture of dark matter in the universe. When rotational velocities stay high far away from the central regions of nearby spiral galaxies – where most of the stars reside – this provides a direct clue that dark matter is there. In fact, scientists believe that each galaxy has a “dark matter halo” that envelops its disc.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/160932/original/image-20170315-5321-1nwse3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/160932/original/image-20170315-5321-1nwse3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=182&fit=crop&dpr=1 600w, https://images.theconversation.com/files/160932/original/image-20170315-5321-1nwse3d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=182&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/160932/original/image-20170315-5321-1nwse3d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=182&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/160932/original/image-20170315-5321-1nwse3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=228&fit=crop&dpr=1 754w, https://images.theconversation.com/files/160932/original/image-20170315-5321-1nwse3d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=228&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/160932/original/image-20170315-5321-1nwse3d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=228&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Dark matter seems to be hiding in our own Milky Way galaxy.</span>
<span class="attribution"><a class="source" href="http://www.eso.org/public/images/milkyway/">Bruno Gilli/ESO -</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Forty years on, and powerful instruments on the <a href="http://www.eso.org/public/unitedkingdom/teles-instr/e-elt/">European Very Large Telescope</a> now allow us to probe extremely distant galaxies: those at the peak epoch of galaxy formation 10 billion years ago. Not only that, by taking deep exposures we can probe the motions of gas all the way out to the outer disk regions of the galaxy. </p>
<p>My colleagues at the Max Planck Institute for Extraterrestrial Physics and I were able to extract the individual rotation curves of six ancient galaxies. And for another 100 galaxies, we managed to combine their measurements into an average curve. Both approaches yielded the same surprising result: in early disk galaxies, the rotation of the outer parts decreases steadily – suggesting there is little or no dark matter there to speed things up.</p>
<h2>The role of dark matter halos</h2>
<p>So how can we explain the findings? Well, we know that there was a lot of gas present in these early galaxies, constantly flowing in from the intergalactic medium. These gas reservoirs make ordinary matter effectively sink to the centres of the dark matter halos that host them, piling up.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/160931/original/image-20170315-5324-6hz7zx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/160931/original/image-20170315-5324-6hz7zx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=563&fit=crop&dpr=1 600w, https://images.theconversation.com/files/160931/original/image-20170315-5324-6hz7zx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=563&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/160931/original/image-20170315-5324-6hz7zx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=563&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/160931/original/image-20170315-5324-6hz7zx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=707&fit=crop&dpr=1 754w, https://images.theconversation.com/files/160931/original/image-20170315-5324-6hz7zx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=707&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/160931/original/image-20170315-5324-6hz7zx.png?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">
<figcaption>
<span class="caption">A simulation of what a dark matter halo might look like, with a galaxy at the dense centre. There are also many satellite galaxies, each with its own subhalo which is visible as a region of high dark matter density in the image.</span>
<span class="attribution"><span class="source">wikipedia</span></span>
</figcaption>
</figure>
<p>It could also be that during these early times the dark matter halos were growing rapidly and were not yet in equilibrium. This means that the odds that galaxies could form in regions of lower dark matter concentration were higher.</p>
<p>Cosmic time scales are long. Mapping the evolutionary paths of galaxies throughout the history of the universe requires piecing together snapshots of their lives, as observed at different epochs. Undoubtedly, our new findings will add a valuable piece to this puzzle. What we can say for now is that the disk galaxies we observed three billion years after the Big Bang are markedly different compared to Milky Way type galaxies today.</p>
<p>But it’s important to remember that when comparing these ancient galaxies to ones ten billion years later, one should also take into account that new stars will be formed in the meantime. In the search for descendant galaxies, it therefore seems more relevant to look at modern galaxies that are more massive than the Milky Way. Those are often <a href="http://astronomynow.com/news/n1106/23galaxies/">spheroidal in shape</a> (they lack spiral arms). Interestingly, their dynamics also point at low dark matter concentrations.</p>
<p>Looking ahead, we want to uncover the physics behind such evolution, and explore how our findings can inform the theory on how normal and dark matter interact. Perhaps it could even help us to answer the biggest question of all: what dark matter really is.</p><img src="https://counter.theconversation.com/content/74352/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stijn Wuyts 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>So where did all the dark matter come from?Stijn Wuyts, Senior Lecturer of Physics, University of BathLicensed 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/674382016-11-01T19:05:46Z2016-11-01T19:05:46ZThe cosmic crime-scene hunt for clues on how galaxies are formed<figure><img src="https://images.theconversation.com/files/143040/original/image-20161025-28376-1xxp128.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Andromeda Galaxy.</span> </figcaption></figure><p>How did large galaxies, like our own <a href="http://www.universetoday.com/22285/facts-about-the-milky-way/">Milky Way</a> and the nearby <a href="http://www.universetoday.com/30289/andromeda-galaxy/">Andromeda Galaxy</a>, emerge from the featureless soup that existed after <a href="https://science.nasa.gov/astrophysics/focus-areas/what-powered-the-big-bang">the birth of our universe</a>?</p>
<p>Decades of observations and theoretical effort have provided a picture in which atoms pool into galaxies, drawn by the gravitational pull of dark matter. Our <a href="http://icc.dur.ac.uk/Eagle/">synthetic universes</a>, created and evolved on the most powerful supercomputers, beautifully match the distribution of galaxies we see on the universe.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/6V021B8FdyQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The formation of cosmological simulation: The EAGLE Simulation.</span></figcaption>
</figure>
<p>Understanding the small-scale detail is going to occupy astronomers <a href="https://www.science.org.au/supporting-science/science-sector-analysis/reports-and-publications/decadal-plan-australian">for decades to come</a>, but it appears that galaxies are built up over time by accreting (gathering) smaller systems that stray too close.</p>
<p>And in the past few decades, it has become clear that the tenuous stellar halo that surrounds large galaxies holds the clues to unravelling galaxies accretion history. </p>
<h2>Dissecting galaxies</h2>
<p>A big <a href="http://cas.sdss.org/dr6/en/proj/basic/galaxies/spirals.asp">spiral galaxy</a> can be split into three key pieces: the bulge, the disk and the halo.</p>
<p>The bulge and disk are home to the vast majority of the hundreds of billions of stars that make up the galaxy, whereas only 1% of the stars can be found in the halo that envelopes a galaxy.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/143229/original/image-20161026-11247-17rh0nl.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/143229/original/image-20161026-11247-17rh0nl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/143229/original/image-20161026-11247-17rh0nl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=360&fit=crop&dpr=1 600w, https://images.theconversation.com/files/143229/original/image-20161026-11247-17rh0nl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=360&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/143229/original/image-20161026-11247-17rh0nl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=360&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/143229/original/image-20161026-11247-17rh0nl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=452&fit=crop&dpr=1 754w, https://images.theconversation.com/files/143229/original/image-20161026-11247-17rh0nl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=452&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/143229/original/image-20161026-11247-17rh0nl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=452&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Dissecting a galaxy.</span>
<span class="attribution"><span class="source">The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The halo hosts some of the <a href="https://www.scientificamerican.com/article/ancient-halo-stars-cast-the-milky-ways-first-light/">oldest stars to be found in a galaxy</a>. It is also home to <a href="http://www.space.com/29717-globular-clusters.html">globular clusters</a>, the oldest bound groups of stars we know in the universe.</p>
<p>These suggest that the halo was the first galactic component to form, and it should hold some of the best preserved record for the formation history of a galaxy.</p>
<p>But to reveal the secrets hidden within a galaxy, astronomers have to take a forensic approach and look at the stellar halo like a crime scene.</p>
<h2>Galactic cannibals</h2>
<p>It is within the stellar halo that smaller <a href="https://www.cfa.harvard.edu/%7Elsales/DwarfGalaxies.html">dwarf galaxies</a> meet their ultimate fate, losing their battle with the destructive forces of gravity.</p>
<p>These dwarf galaxies are stripped, harassed and dispersed until they eventually mix with the stars of the larger galaxy. </p>
<p>But this destruction, this <a href="http://www.universetoday.com/89086/galactic-cannibalism/">galactic cannibalism</a>, can take many billions of years, and we expect to catch the ongoing destruction of dwarf galaxies even today. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/142600/original/image-20161021-8862-11qhiny.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/142600/original/image-20161021-8862-11qhiny.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/142600/original/image-20161021-8862-11qhiny.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/142600/original/image-20161021-8862-11qhiny.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/142600/original/image-20161021-8862-11qhiny.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/142600/original/image-20161021-8862-11qhiny.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/142600/original/image-20161021-8862-11qhiny.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/142600/original/image-20161021-8862-11qhiny.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">The stellar substructure seen in the halo of Andromeda as revealed in the PAndAS. The stars have been colour-coded based upon their metallicity, a measure of their chemical enrichment. Metal-rich stars appear red, whereas metal-poor as blue.</span>
<span class="attribution"><span class="source">The Pan-Andromeda Archaeological Survey view of the Andromeda Satellite System by Ibata et. al. (2013)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>There is observational evidence for the existence of a range of substructures in galaxy halos, such as tidal streams and stellar shells, revealed in our own Milky Way and the neighbouring <a href="http://space-facts.com/andromeda/">Andromeda Galaxy</a>.</p>
<p>It is within these galaxies that we can identify and isolate individual stars within the extremely faint halo. And it was the halo of Andromeda that formed the focus for <a href="https://arxiv.org/abs/1610.01158v1">our new study</a> published recently.</p>
<h2>A search for clustering</h2>
<p>Instead of stars, we used a map of the <a href="http://www.space.com/17715-planetary-nebula.html">planetary nebulae</a> that also inhabit the halo of Andromeda.</p>
<p>These are the late-stage evolution of stars similar to our own sun, stars that are the debris of disrupting and disrupted dwarf galaxies. Luckily, these are readily identifiable due to their peculiar <a href="http://web.williams.edu/Astronomy/research/PN/nebulae/">spectral signature</a>, a signature that also reveals their velocities. </p>
<p>We needed to pick over these galactic corpses, dissecting the crime scene to work out just how many victims lay hidden in plain sight.</p>
<p>To do this, we looked for how “<a href="https://en.wikipedia.org/wiki/Cluster_analysis">clustered</a>” these planetary nebulae are.</p>
<p>If the picture of halos growing through accretion is correct, then we should expect an underlying smooth and unclustered distribution, the remnants of ancients accretions that have been completely disrupted and mixed, overlaid with ongoing accretions that should be clustered together in space and velocity. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/142612/original/image-20161021-8865-wd4xzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/142612/original/image-20161021-8865-wd4xzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/142612/original/image-20161021-8865-wd4xzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/142612/original/image-20161021-8865-wd4xzv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/142612/original/image-20161021-8865-wd4xzv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/142612/original/image-20161021-8865-wd4xzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/142612/original/image-20161021-8865-wd4xzv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/142612/original/image-20161021-8865-wd4xzv.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">A simulated halo of a galaxy like Andromeda. The halo is filled with the debris of tidally disrupted substructure.</span>
<span class="attribution"><a class="source" href="http://www.ras.org.uk/news-and-press/157-news2010/1856-galactic-archaeologists-find-origin-of-milky-ways-ancient-stars">Andrew Cooper, John Helly (Durham University)</a></span>
</figcaption>
</figure>
<p>But there are problems. While we can see where the planetary nebulae are in the sky, and we can measure the velocity along the <a href="http://spiff.rit.edu/classes/phys301/lectures/doppler/doppler.html">line-of-sight</a>, distances are unknown, as are the <a href="http://astronomy.swin.edu.au/cosmos/P/Proper+motion">proper motions</a> in the plane of the sky.</p>
<p>We had to develop some clever methods to search for clustering signatures, and compare these to expectations drawn from synthetic models of galaxies. </p>
<p>And success! The results revealed a mix of smoothly scrambled and lumpy clustered planetary nebulae, precisely in accordance with our cosmological expectations. </p>
<p>This provides further evidence for our current best explanation for the cosmos, the <a href="http://cosmology.berkeley.edu/Education/CosmologyEssays/The_Standard_Cosmology.html">Lambda Cold Dark Matter cosmological model</a>, a universe dominated by the gravitational pull of dark matter battling the expansion of the universe, and where galaxies have been steadily built up over time through devouring smaller systems.</p>
<p>While this success is heartening, with growing evidence that our understanding of the workings of the universe is well founded, tensions remain. This is particularly so on the scale of individual halos of large galaxies – the recently discovered <a href="https://theconversation.com/a-cosmic-two-step-the-universal-dance-of-the-dwarf-galaxies-29472">coordinated dance of dwarf galaxies</a> still cries out for an answer.</p>
<p>Astronomical effort will continue over the next few decades, but on the question of when we will truly understand galaxy formation and evolution, the jury is still out.</p><img src="https://counter.theconversation.com/content/67438/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><p class="fine-print"><em><span>Prajwal R. Kafle receives funding from the Australian Research Council and University of Western Australia. </span></em></p>Astronomers have taken a forensic approach to study the stellar halo of a galaxy to reveal hidden secrets on how such galaxies were formed.Geraint Lewis, Professor of Astrophysics, University of SydneyPrajwal Kafle, Research Associate| Lecturer, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/672732016-10-19T22:29:57Z2016-10-19T22:29:57ZUnder the Milky Way: what a new map reveals about our galaxy<figure><img src="https://images.theconversation.com/files/142389/original/image-20161019-20340-bti15y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Milky Way as seen from Earth.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/ozdz/14083652247/">Flickr/Peter Ozdzynski </a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Look up on any clear night and if you’re lucky you may be able to see part of the <a href="https://theconversation.com/explainer-a-beginners-guide-to-the-galaxy-49">Milky Way</a> stretching across the sky.</p>
<p>For many thousands of years that was all people could see of our galaxy, though today light pollution means even <a href="http://news.nationalgeographic.com/2016/06/milky-way-space-science/">that view is now fading</a> for many naked-eye observers.</p>
<p>Even for astronomers, much of our galaxy is obscured from view in the visible light spectrum, including the <a href="http://www.universetoday.com/120006/why-cant-we-see-the-center-of-the-milky-way/">galactic centre</a>.</p>
<p>Our view of the Milky Way has also come a long way since the first observation on March 25, 1951, of the famous 21-cm neutral hydrogen line by Harvard astronomers <a href="https://www.britannica.com/science/radio-astronomy#ref960941">Harold Ewen and Edward Purcell</a>.</p>
<p>Dutch astronomer <a href="https://www.britannica.com/biography/Hendrik-Christoffel-van-de-Hulst">Hendrik van de Hulst</a> in the 1940s had provided the first prediction of the existence of this faint cosmic emission, the detection of which was to revolutionise radio astronomy.</p>
<p>Observations of signals at this wavelength by radio telescopes allowed the spiral structure of the Milky Way to be seen for the first time.</p>
<h2>A clearer view</h2>
<p>Today sees the opening of a new chapter of discovery with the release of a brand new view of the Milky Way, <a href="http://s3-ap-southeast-2.amazonaws.com/icrar.org/wp-content/uploads/2016/10/12102646/bwinkel_langedit_printer.pdf">published in the journal Astronomy and Astrophysics</a>.</p>
<p>The map stems from a decade of analysis and thousands of hours of observing time on the 64-metre CSIRO Parkes radio telescope in New South Wales, Australia, and the 100-metre Max-Planck radio telescope in Effelsberg, Germany.</p>
<p>The outcome is a brand new hydrogen image of the Milky Way and its environment with a level of detail that is at least four times better than previous images.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/142377/original/image-20161019-20313-1y4zr0p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/142377/original/image-20161019-20313-1y4zr0p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/142377/original/image-20161019-20313-1y4zr0p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/142377/original/image-20161019-20313-1y4zr0p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/142377/original/image-20161019-20313-1y4zr0p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/142377/original/image-20161019-20313-1y4zr0p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/142377/original/image-20161019-20313-1y4zr0p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/142377/original/image-20161019-20313-1y4zr0p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&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 HI4PI image colours reflect gas at differing velocities. The plane of the Milky Way runs horizontally across the middle and the Magellanic Clouds can be seen at the lower right.</span>
<span class="attribution"><span class="source">Benjamin Winkel and the HI4PI collaboration</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The importance of the new HI4PI image (as we call it) can be seen from the fact that the previous best but blurry image of hydrogen gas in the Milky Way, <a href="http://www.aanda.org/articles/aa/abs/2005/35/aa1864-04/aa1864-04.html">published in 2005</a>, has so far been cited more than 1,700 times in scientific articles published in peer-reviewed journals.</p>
<p>Was it necessary to use observations of the whole northern and southern skies? Yes, because we live inside the Milky Way and we are entirely surrounded by it. </p>
<p>So the new image is a view from inside, and not an impossible view from outside. </p>
<h2>New structure to our galaxy</h2>
<p>By examining the motion of the hydrogen clouds towards or away from us (caused by the spin of the Milky Way), a good model of the Milky Way’s structure can be inferred.</p>
<p>The Australian team leader Naomi McClure-Griffiths, from the Australian National University, has already used the Parkes data to discover a new outer arm of the Milky Way.</p>
<p>Why did it take a decade to produce? Largely because the data not only had to be calibrated and imaged with new algorithms, but also had to be cleaned of terrestrial and cosmic noise. </p>
<p>Terrestrial noise comes from illegal transmissions in the 21-cm radio band. This part of the radio spectrum is protected by international treaty but we frequently detect emissions, usually caused by faulty or badly designed equipment outside (and occasionally inside) the observatories. </p>
<p>Cosmic noise comes from strong emissions which leak into the telescope from other parts of the sky, similar to trying to observe the night sky when there is a bright street lamp in the corner of your eye. </p>
<p>Fortunately, team member Peter Kalberla from the University of Bonn, Germany, was able to digitally remove these artefacts by using sophisticated models of the telescopes combined with carefully using the annual variation of the spurious signal provided by the orbit of the Earth around the Sun.</p>
<p>Other colleagues, including Benjamin Winkel and Juergen Kerp, were able to painstakingly crossmatch and patch together the two hemispheres into a uniform image of the Milky Way across the whole sky.</p>
<figure>
<iframe src="https://player.vimeo.com/video/187588691" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
</figure>
<p>The hydrogen data from the two telescopes has already provided many scientific discoveries. The newly combined data will allow even more discoveries. </p>
<p>For example, we will be able to trace for the first time at this level of detail, the complete path of the <a href="https://www.scientificamerican.com/article/star-performers-the-magellanic-clouds/">stream of hydrogen being pulled</a> from the Magellanic Clouds by the Milky Way.</p>
<p>The enormously strong tide created by our Milky Way has pulled out a long tail of gas from the clouds, which extends across almost the whole sky.</p>
<p>Just as importantly the new data set is now available to all astronomers and will provide a valuable resource for future research.</p>
<p>X-ray astronomers, for example, will be able to use the data to better correct their data for interstellar absorption and better understand the intense emission associated with distant supermassive black holes.</p>
<p>A word of warning though for those wishing to download the whole data set – it’s about 188 gigabytes. Our receivers were simultaneously tuned to thousands of different frequencies. This allowed us to look at hydrogen at many different redshifts (using the so-called Doppler effect).</p>
<p>So the underlying data set is vastly larger than the simple intensity and velocity images shown here! But who knows what other new discoveries the data will reveal?</p><img src="https://counter.theconversation.com/content/67273/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lister Staveley-Smith receives research funding from the Australian Research Council and the Western Australian government. </span></em></p>Astronomers are making new discoveries about our galaxy thanks to a more detailed map of the Milky Way.Lister Staveley-Smith, Science Director at the International Centre for Radio Astronomy Research (ICRAR) and Deputy Director of the ARC Centre for All-sky Astrophysics (CAASTRO), The University of Western AustraliaLicensed 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/593732016-06-13T20:07:23Z2016-06-13T20:07:23ZHow citizen scientists discovered a giant cluster of galaxies<figure><img src="https://images.theconversation.com/files/123496/original/image-20160523-9565-nfgf8r.png?ixlib=rb-1.1.0&rect=3%2C261%2C1053%2C642&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The new discovery: The C-shaped “wide angle tail galaxy” (pink) surrounded by the galaxies of the Matorny-Terentev cluster (white).</span> <span class="attribution"><span class="source">Julie Banfield</span>, <span class="license">Author provided</span></span></figcaption></figure><p>It used to be that you had to have years of training before you could participate in cutting-edge science.</p>
<p>But that has changed, with the power of the internet enabling thousands of ordinary people to contribute to one of humanity’s most exciting endeavours from the comfort of their homes.</p>
<p><a href="http://mnras.oxfordjournals.org/content/early/2016/05/05/mnras.stw1067">It was announced</a> in May that a cluster of galaxies millions of light years away was discovered by a team of citizen scientists clicking on images on their computers at home.</p>
<h2>Citizen science</h2>
<p>Citizen Science first became prominent in 2006 with the launch of <a href="http://stardustathome.ssl.berkeley.edu/">Stardust@home</a> by the University of California-Berkeley, quickly followed in 2007 by <a href="https://www.galaxyzoo.org/">Galaxy Zoo</a>, which aimed to classify galaxies from optical images.</p>
<p>Now, many such citizen science projects span all fields of science from astronomy to biology. </p>
<p>The idea is simple: the average human brain is far superior to our most powerful computers when it comes to problems like image recognition.</p>
<p>So citizen science projects combine the brainpower of thousands of ordinary people to solve some of science’s most challenging problems. </p>
<p>What do the citizen scientists get out of it? In most cases, the knowledge that they are helping to expand the frontiers of human knowledge. And perhaps the chance of making a truly great discovery.</p>
<h2>The EMU project</h2>
<p>The Evolutionary Map of the Universe (<a href="http://www.atnf.csiro.au/people/Ray.Norris/emu/index.html">EMU</a>) project will survey the radio sky using CSIRO’s new A$165-million <a href="http://www.atnf.csiro.au/projects/askap">ASKAP</a> telescope being built in Western Australia, to understand how galaxies form and evolve.</p>
<p>We expect EMU to discover about 70-million galaxies from their radio emission, compared to the 2.5-million so far known. </p>
<p>But we have a problem: to get the best science, we need to cross-match these radio sources with galaxies spotted by infrared and optical telescopes, and no research team has enough members to match 70-million objects by eye.</p>
<p>About half of EMU’s radio sources are galaxies like our own Milky Way, with radio emission resulting from the debris of star formation, so that the radio source is easily matched to the optical galaxy. </p>
<p>The other half are caused by jets of electrons squirting out from a massive black hole at the centre of the galaxy, producing two giant blobs of radio emission either side of the galaxy.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/123306/original/image-20160520-4481-1rv64ju.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/123306/original/image-20160520-4481-1rv64ju.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/123306/original/image-20160520-4481-1rv64ju.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=426&fit=crop&dpr=1 600w, https://images.theconversation.com/files/123306/original/image-20160520-4481-1rv64ju.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=426&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/123306/original/image-20160520-4481-1rv64ju.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=426&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/123306/original/image-20160520-4481-1rv64ju.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=535&fit=crop&dpr=1 754w, https://images.theconversation.com/files/123306/original/image-20160520-4481-1rv64ju.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=535&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/123306/original/image-20160520-4481-1rv64ju.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=535&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 radio galaxy (Hercules A) powered by a black hole, based on image from the National Radio Astronomy Observatory, showing the radio emission (red) superimposed on the optical emission (white).</span>
<span class="attribution"><span class="source">Credits for original image: NASA, ESA, S. Baum and C O'Dea (RIT), R Perley and W Cotton (NRAO/AUI/NS), and the Hubble Heritage Team (STScI/AURA)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>EMU will see them as three blobs of emission in a line. But how can you distinguish one of these triple monsters from a line of three single galaxies like the Milky Way? It’s hard. </p>
<p>Clever automated algorithms, such as neural networks, are still in their infancy, and not yet up to the task. But the human brain is really good at this. </p>
<p>In 2010 I visited Chris Lintott at the University of Oxford. Chris was one of the founders of Galaxy Zoo, and I wanted to know if we could build something like Galaxy Zoo to solve EMU’s problem.</p>
<h2>The Radio Galaxy Zoo</h2>
<p>And thus Radio Galaxy Zoo (<a href="https://radio.galaxyzoo.org/">RGZ</a>) was born, with two young scientists, Julie Banfield from ANU, and Ivy Wong from the University of Western Australia, taking over responsibility for leading it.</p>
<figure class="align-center zoomable">
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<figcaption>
<span class="caption">A screenshot from RGZ.</span>
<span class="attribution"><span class="source">Radio Galaxy Zoo</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>After two years of designing the interface, and trying out prototypes, RGZ was launched in December 2013. Since then, RGZ has been enormously successful, with about 10,000 people matching up the sources, resulting in some 1.6 million cross-matches.</p>
<p>Mainstream science moves forward on two different paths. Perhaps the better known is the painstaking analysis needed to test a hypothesis or understand how something works, like searching for the <a href="http://home.cern/topics/higgs-boson">Higgs boson</a> with the Large Hadron Collider.</p>
<p>This way solves the “known unknowns” of science. The other path is when scientists unexpectedly stumble across something they weren’t looking for and weren’t expecting – an “unknown unknown”, such as <a href="https://theconversation.com/explainer-the-mysterious-dark-energy-that-speeds-the-universes-rate-of-expansion-40224">Dark Energy</a>.</p>
<p>Citizen Science is the same. Radio Galaxy Zoo asks people to match up images taken with radio telescopes with those taken with infrared telescopes. It’s hard work, but very important if we are to make sense of our universe. </p>
<p>Occasionally, they stumble across major discoveries.</p>
<h2>Galaxy cluster</h2>
<p>Two Russian citizen scientists, <a href="https://blog.galaxyzoo.org/2016/04/18/exclusive-interview-with-our-recent-citizen-science-co-authors/">Ivan Terentev and Tim Matorny</a>, were cross-matching the radio and infrared sources in RGZ, when they noticed something odd about one of the radio sources.</p>
<p>“They found something that none of us had even thought would be possible,” Dr Banfield said.</p>
<p>What the Russians had found was just one of a line of radio blobs that delineate a C-shaped “wide angle tail galaxy”.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/123308/original/image-20160520-4484-fnvilz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/123308/original/image-20160520-4484-fnvilz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/123308/original/image-20160520-4484-fnvilz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=426&fit=crop&dpr=1 600w, https://images.theconversation.com/files/123308/original/image-20160520-4484-fnvilz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=426&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/123308/original/image-20160520-4484-fnvilz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=426&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/123308/original/image-20160520-4484-fnvilz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=535&fit=crop&dpr=1 754w, https://images.theconversation.com/files/123308/original/image-20160520-4484-fnvilz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=535&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/123308/original/image-20160520-4484-fnvilz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=535&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 C-shaped ‘wide angle tail galaxy’, showing the jets blown back as the galaxy flies through the intergalactic gas. Diagram by the author, based on image from National Radio Astronomy Observatory.</span>
<span class="attribution"><span class="source">Associated Universities, Inc</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>These rare objects are caused by electron jets ejected from a massive black hole, but in this case they are blown sideways by their flight through the intergalactic gas, making them bend into a C shape.</p>
<p>The characteristic bent tails are a sure sign that there is intergalactic gas, signifying a cluster of galaxies, the largest known objects in the universe. </p>
<p>The wide-angle tail galaxy discovered by Terentev and Matorny is one of the largest known, and its host cluster is now known as the Matorny-Terentev cluster. </p>
<p>This cluster, more than a billion light years away, contains at least 40 galaxies, marking an intersection of the sheets and filaments of the cosmic web that make up our universe. </p>
<p>Despite their cosmic importance, clusters are notoriously hard to find, and wide angle tail galaxies may turn out to be one of the best ways of finding them. </p>
<p>Nevertheless, finding the wide angle tails themselves amongst the millions of radio sources is like finding a needle in a haystack.</p>
<p>The discovery was detailed in a <a href="http://mnras.oxfordjournals.org/content/early/2016/05/05/mnras.stw1067">paper published</a> this month in the Monthly Notices of the Royal Astronomical Society.</p>
<p>Clusters are poorly understood, but are key to understanding how our universe is put together. This discovery takes us a step closer to figuring it out.</p>
<p>So what’s next? Obviously, RGZ will continue, and who knows what other discoveries may emerge. But not even RGZ is fast enough to classify all of EMU’s 70-million galaxies, and our <a href="https://theconversation.com/machine-learning-and-big-data-know-it-wasnt-you-who-just-swiped-your-credit-card-48561">machine learning</a> algorithms are too dumb to do it well. </p>
<p>So, instead, we will harness the power of RGZ to train our machine-learning algorithms. Future RGZ citizen scientists will not just be classifying galaxies, they will be teaching the next-generation algorithms how to do it.</p><img src="https://counter.theconversation.com/content/59373/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ray Norris 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 find by citizen scientists of at least 40 galaxies in a cluster more than a billion light years away is the astronomical equivalent of finding a needle in a haystack.Ray Norris, Professor, School of Computing, Engineering, & Maths, Western Sydney UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/521162015-12-11T09:25:19Z2015-12-11T09:25:19ZRarity of Jupiter-like planets means planetary systems exactly like ours may be scarce<figure><img src="https://images.theconversation.com/files/105138/original/image-20151209-15588-1cyskbt.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's depiction of the newly discovered Jupiter-like planet orbiting the star HD 32963. </span> <span class="attribution"><span class="source">Stefano Meschiari</span></span></figcaption></figure><p>Is our little corner of the galaxy a special place? As of this date, we’ve <a href="http://exoplanets.org">discovered more than 1,500 exoplanets</a>: planets orbiting stars other than our sun. Thousands more will be added to the list in the coming years as we confirm planetary candidates by alternative, independent methods.</p>
<p>In the hunt for other planets, we’re especially interested in those that might potentially host life. So we focus our modern exoplanet surveys on planets that might be similar to Earth: low-mass, rocky and with just the right temperature to allow for liquid water. But what about the other planets in the solar system? The <a href="https://en.wikipedia.org/wiki/Copernican_principle">Copernican principle</a> – the idea that the Earth and the solar system are not unique or special in the universe – suggests the architecture of our planetary system should be common. But it doesn’t seem to be.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105306/original/image-20151210-7425-1kd373r.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105306/original/image-20151210-7425-1kd373r.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105306/original/image-20151210-7425-1kd373r.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=429&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105306/original/image-20151210-7425-1kd373r.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=429&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105306/original/image-20151210-7425-1kd373r.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=429&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105306/original/image-20151210-7425-1kd373r.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=539&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105306/original/image-20151210-7425-1kd373r.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=539&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105306/original/image-20151210-7425-1kd373r.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=539&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 mass-period diagram. Each dot marks the mass and orbital period of a confirmed exoplanet.</span>
<span class="attribution"><span class="source">Stefano Meschiari</span></span>
</figcaption>
</figure>
<p>The figure above, called a <em>mass-period diagram</em>, provides a visual way to compare the planets of our solar system with those we’ve spotted farther away. It charts the orbital periods (the time it takes for a planet to make one trip around its central star) and the masses of the planets discovered so far, compared with the properties of solar system planets.</p>
<p>Planets like Earth, Jupiter, Saturn and Uranus occupy “empty” parts of the diagram – we haven’t found other planets with similar masses and orbits so far. At face value, this would indicate that the majority of planetary systems do not resemble our own solar system.</p>
<p>The solar system lacks close-in planets (planets with orbital periods between a few and a few tens of days) and super-Earths (a class of planets with masses a few times the mass of the Earth often detected in other planetary systems). On the other hand, it does feature several long-period gaseous planets with very nearly circular orbits (Jupiter, Saturn, Uranus and Neptune). </p>
<p>Part of this difference is due to selection effects: close-in, massive planets are easier to discover than far-out, low-mass planets. In light of this discovery bias, astronomers <a href="http://aasnova.org/2015/09/25/how-normal-is-our-solar-system/">Rebecca Martin and Mario Livio</a> convincingly argue that our solar system is actually <a href="http://dx.doi.org/10.1088/0004-637X/810/2/105">more typical than it seems at first glance</a>.</p>
<p>There is a sticking point, however: Jupiter still stands out. It’s an outlier based both on its orbital location (with a corresponding period of about 12 years) and its very-close-to-circular orbit. Understanding whether Jupiter’s relative uniqueness is a real feature, or another product of selection effects, has real implications for our understanding of exoplanets.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/3afEX8a2jPg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Jupiter as seen by the Hubble Space Telescope.</span></figcaption>
</figure>
<h2>Throwing its weight around</h2>
<p>According to our understanding of how our solar system formed, Jupiter shaped much of the other planets’ early history. Due to its gravity, it influenced the <a href="http://www.sciencedaily.com/releases/2011/06/110605132437.htm">formation of Mars</a> and Saturn. It potentially facilitated the development of life by shielding Earth from cosmic collisions that would have delayed or extinguished it, and by funneling water-rich bodies towards it. And its gravity <a href="http://doi.org/10.1073/pnas.1423252112">likely swept the inner solar system of solid debris</a>. Thanks to this clearing action, Jupiter might have prevented the formation of super-Earth planets with massive atmospheres, thereby ensuring that the inner solar system is populated with small, rocky planets with thin atmospheres. </p>
<p>Without Jupiter, it looks unlikely that we’d be here. As a consequence, figuring out if Jupiter is a relatively common type of planet might be crucial to understanding whether terrestrial planets with a similar formation environment as Earth are abundant in the galaxy.</p>
<p>Despite their relative heft, it’s a challenge to discover Jupiter analogs – those planets with periods and masses similar to Jupiter’s. Astronomers typically discover them using an indirect detection technique called the <a href="https://en.wikipedia.org/wiki/Doppler_spectroscopy">Doppler radial velocity method</a>. The gravitational pull of the planet causes tiny shifts in the wavelength of features in the spectrum of the star, in a distinctive, periodic pattern. We can detect these shifts by periodically capturing the star’s light with a telescope and turning it into a spectrum with <a href="https://www2.keck.hawaii.edu/inst/hires/">a spectrograph</a>. This periodic signal, based on a planet’s long orbital period, can require monitoring a star over many years, even decades.</p>
<h1>Are Jupiter-like planets rare?</h1>
<p><a href="http://arxiv.org/abs/1512.00417">In a recent paper</a>, Dominick Rowan, a high school senior from New York, and his coauthors (including astronomers from the University of Texas, the University of California at Santa Cruz and me) analyzed the Doppler data for more than 1,100 stars. Each star was observed with the <a href="http://www.keckobservatory.org/">Keck Observatory telescope</a> in Hawaii; many of them had been monitored for a decade or more. To analyze the data, he used the <a href="https://www.r-project.org">open-source statistical environment R</a> together with a freely available application that I developed, called <a href="http://www.stefanom.org/systemic">Systemic</a>. Many universities use an <a href="http://www.stefanom.org/systemic-live">online version</a> to teach how to analyze astronomical data.</p>
<p>Our team studied the available data for each star and calculated the probability that a Jupiter-like planet could have been missed – either because not enough data are available, or because the data are not of high enough quality. To do this, we simulated hundreds of millions of possible scenarios. Each was created with a computer algorithm and represents a set of alternative possible observations. This procedure makes it possible to infer how many Jupiter analogs (both discovered and undiscovered) orbited the sample of 1,100 stars.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/105134/original/image-20151209-15552-1nqxyfv.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105134/original/image-20151209-15552-1nqxyfv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105134/original/image-20151209-15552-1nqxyfv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105134/original/image-20151209-15552-1nqxyfv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105134/original/image-20151209-15552-1nqxyfv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105134/original/image-20151209-15552-1nqxyfv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105134/original/image-20151209-15552-1nqxyfv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105134/original/image-20151209-15552-1nqxyfv.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">Orbit of the newly discovered Jupiter-mass planet orbiting the star HD 32963, compared to the orbits of Earth and Jupiter around the sun.</span>
<span class="attribution"><span class="source">Stefano Meschiari</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>While carrying out this analysis, we discovered a <a href="http://exoplanet.eu/catalog/hd_32963_b/">new Jupiter-like planet</a> orbiting HD 32963, which is a star very similar to the sun in terms of age and physical properties. To make this discovery, we analyzed each star with an automated algorithm that tried to uncover periodic signals potentially associated with the presence of a planet.</p>
<p>We pinpointed the frequency of Jupiter analogs across the survey at approximately 3%. This result is broadly consistent with previous estimates, which were based on a smaller set of stars or a different discovery technique. It greatly strengthens earlier predictions because we took <em>decades</em> of observations into account in the simulations. </p>
<p>This result has several consequences. First, the relative rarity of Jupiter-like planets indicates that true solar system analogs should themselves be rare. By extension, given the important role that Jupiter played at all stages of the formation of the solar system, Earth-like habitable planets with similar formation history to our solar system will be rare.</p>
<p>Finally, it also underscores that Jupiter-like planets do not form as readily around stars as other types of planets do. It could be because not enough solid material is available, or because these gas giants migrate closer to the central stars very efficiently. <a href="http://astrobites.org/2015/08/18/giant-planets-from-far-out-there/">Recent planet-formation simulations</a> tentatively bear out the latter explanation.</p>
<p>Long-running, ongoing surveys will continue to help us understand the architecture of the outer regions of planetary systems. Programs including the Keck planet search and the <a href="http://arxiv.org/abs/1512.02965">McDonald Planet Search</a> have been accumulating data for decades. Discovering ice giants similar to Uranus and Neptune will be even tougher than tracking down these Jupiter analogs. Because of their long orbital periods (84 and 164 years) and the very small Doppler shifts they induce on their central stars (tens of times smaller than a Jupiter-like planet), the detection of Uranus and Neptune analogs lies far in the future.</p><img src="https://counter.theconversation.com/content/52116/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stefano Meschiari works for the University of Texas at Austin.</span></em></p>Jupiter had a big influence on how our solar system’s planets formed. New research – led by a high school student – tried to nail down how rare Jupiter analogs really are in other planetary systems.Stefano Meschiari, W J McDonald Postdoctoral Fellow, The University of Texas at AustinLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/469532015-09-01T18:00:28Z2015-09-01T18:00:28ZMove over Milky Way, elliptical galaxies are the most habitable in the cosmos<figure><img src="https://images.theconversation.com/files/93548/original/image-20150901-13422-iotrh.jpg?ixlib=rb-1.1.0&rect=12%2C505%2C2846%2C2204&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Elliptical galaxy SDSS J162702.56+432833.9 could be full of life.</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Elliptical_galaxy#/media/File:SDSS_J162702.56%2B432833.9.jpg">NASA/ESA/wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>The search for extraterrestrial life is surely one of the most important tasks we humans can undertake. However, the cosmos is vast and we don’t really have any idea which bits of it are actually habitable. But what if we could target the search? We have built the <a href="http://iopscience.iop.org/2041-8205/810/1/L2/article;jsessionid=35758CF547C6B0BE721637C07F4EB179.c1">first-ever “cosmobiological” model</a> mapping the galaxies in our local universe to help us understand which ones are habitable. Surprisingly, we found that our own galaxy was not one of the top candidates.</p>
<h2>Ingredients for habitability</h2>
<p>Drawing on our understanding of habitable zones within a galaxy, we proposed that the overall habitability of any galaxy depends on three key astrophysical criteria. One is simply the total number of stars capable of hosting planets, which is roughly related to the size of the galaxy. Another is the total amount of the building blocks of planets and life – such as carbon, oxygen and iron – the so-called astrophysical “metals”. Another is the negative influence of supernova explosions, whose powerful (and poisonous) radiation could potentially <a href="http://www.nature.com/nature/journal/v265/n5592/abs/265318a0.html">inhibit the formation and evolution of complex life</a> on nearby planets.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93625/original/image-20150902-6144-1toesbp.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">Not so special anymore. Artist s impression of the Milky Way.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Milky_Way#/media/File:Artist%27s_impression_of_the_Milky_Way_%28updated_-_annotated%29.jpg">NASA</a></span>
</figcaption>
</figure>
<p>Interestingly, the largest survey of its kind ever undertaken, data from the <a href="http://www.sdss.org/">Sloan Digital Sky Survey</a> observes exactly these three key properties for more than 150,000 galaxies in the nearby universe. This data shows that the largest galaxies have the largest amount of metals. Sifting through this data set we found that giant <a href="http://www.space.com/22395-elliptical-galaxies.html">elliptical galaxies</a>, which have a rounded shape rather than spiral arms like our Milky Way, win the “most-likely-to-be-habitable” title. Indeed, each giant elliptical that is at least twice as big as the Milky Way and has a tenth of its supernova rate could potentially host 10,000 times as many habitable (Earth-like) planets. </p>
<p>Our results, <a href="http://iopscience.iop.org/2041-8205/810/1/L2/article;jsessionid=35758CF547C6B0BE721637C07F4EB179.c1">recently published</a> in the Astrophysical Journal Letters, also show that they typically have a low rate of supernova explosions, ensuring that most of these planets remain unmolested by harmful radiation.</p>
<p>This is the first computation that discusses life on cosmological scales, rather than just within individual galaxies like the Milky Way. The model therefore opens up a new avenue, extending the understanding of habitability around individual stars to a true “cosmobiological” context, which allows us to discuss the habitability of the entire universe. </p>
<p>One of the most attractive features of the model is that that data used includes the entire history of all the galaxies in the universe that we see around us. The relationship between the number of stars, amount of metals and rate of supernova explosions essentially acts as the “fingerprint”, uniquely identifying how any given galaxy formed. This is a key bit of information that we need to understand the chances of galactic habitability and which has been missing in this field. </p>
<h2>Are we in the wrong galaxy?</h2>
<p>By all accounts, our Milky Way is a typical <a href="http://cas.sdss.org/dr6/en/proj/basic/galaxies/spirals.asp">spiral galaxy</a> of average size that roughly makes one star like our sun every year. Given that ellipticals are much more hospitable to habitable planets raises the interesting question of whether life here in the Milky Way is just a freak of nature. </p>
<p>Or does the presence of life on at least one planet in the Milky Way imply that these big elliptical galaxies might be absolutely teeming with life?</p>
<p>One drawback is that the nearest elliptical galaxy to the Milky Way, called <a href="http://www.astr.ua.edu/gifimages/maffei1.html">Maffei1</a>, is so far away that any radio signals beamed from this cosmic neighbour would take 9m years to reach us. Surveys such as the <a href="https://theconversation.com/its-not-all-about-aliens-listening-project-may-unveil-other-secrets-of-the-universe-45031">SETI (Search for Extraterrestrial Intelligence)</a> that continually maps the skies for anomalous signals might one day detect such a signal in the far future, a call to us from our (not so) nearest neighbours. </p>
<p><em>Read other articles from our cosmology series <a href="https://theconversation.com/uk/topics/cosmology-series">here</a></em></p><img src="https://counter.theconversation.com/content/46953/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Pratika Dayal 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 new model suggests that elliptical galaxies are more likely to be habitable than spiral galaxies like our own. Does that mean we’re a freak event and elsewhere is teeming with life?Pratika Dayal, Addison Wheeler Fellow in Cosmology, Durham UniversityLicensed as Creative Commons – attribution, no derivatives.