tag:theconversation.com,2011:/au/topics/galaxy-clusters-76205/articlesgalaxy clusters – The Conversation2023-02-15T19:07:04Ztag:theconversation.com,2011:article/1997852023-02-15T19:07:04Z2023-02-15T19:07:04ZThe largest structures in the Universe are still glowing with the shock of their creation<figure><img src="https://images.theconversation.com/files/515372/original/file-20230315-16-i6oy82.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Screenshot at</span> </figcaption></figure><p>On the largest scales, the Universe is ordered into a web-like pattern: galaxies are pulled together into clusters, which are connected by <a href="https://theconversation.com/a-thread-of-the-cosmic-web-astronomers-spot-a-50-million-light-year-galactic-filament-151569">filaments</a> and separated by voids. These clusters and filaments contain dark matter, as well as regular matter like gas and galaxies. </p>
<p>We call this the “<a href="https://bigthink.com/hard-science/cosmic-web/">cosmic web</a>”, and we can see it by mapping the locations and densities of galaxies from large surveys made with optical telescopes. </p>
<p>We think the cosmic web is also permeated by magnetic fields, which are created by energetic particles in motion and in turn guide the movement of those particles. Our theories predict that, as gravity draws a filament together, it will cause shockwaves that make the magnetic field stronger and create a glow that can be seen with a radio telescope.</p>
<p>In <a href="http://www.science.org/doi/10.1126/sciadv.ade7233">new research published in Science Advances</a>, we have for the first time observed these shockwaves around pairs of galaxy clusters and the filaments that connect them.</p>
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Read more:
<a href="https://theconversation.com/explainer-radio-astronomy-7420">Explainer: radio astronomy</a>
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<p>In the past, we have only ever observed these radio shockwaves directly from <a href="https://theconversation.com/we-found-some-strange-radio-sources-in-a-distant-galaxy-cluster-theyre-making-us-rethink-what-we-thought-we-knew-187631">collisions between galaxy clusters</a>. However, we believe they exist around small groups of galaxies, as well as in cosmic filaments. </p>
<p>There are still gaps in our knowledge of these magnetic fields, such as how strong they are, how have they evolved, and what their role is in the formation of this cosmic web. </p>
<p>Detecting and studying this glow could not only confirm our theories for how the large-scale structure of the Universe has formed, but help answer questions about cosmic magnetic fields and their significance. </p>
<h2>Digging into the noise</h2>
<p>We expect this radio glow to be both very faint and spread over large areas, which means it is very challenging to detect it directly. </p>
<p>What’s more, the galaxies themselves are much brighter and can hide these faint cosmic signals. To make it even more difficult, the noise from our telescopes is usually many times larger than the expected radio glow. </p>
<p>For these reasons, rather than <em>directly</em> observing these radio shockwaves, we had to get creative, using a technique known as stacking. This is when you average together images of many objects too faint to see individually, which decreases the noise, or rather enhances the average signal above the noise. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a stack of several faint images next to a single sharper version of the image." src="https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=420&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=420&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509753/original/file-20230213-25-ko9ipi.png?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">‘Stacking’ many images together can make the signal of interest brighter than the background noise.</span>
<span class="attribution"><span class="source">Tessa Vernstrom</span>, <span class="license">Author provided</span></span>
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<p>So what did we stack? We found more than 600,000 pairs of galaxy clusters that are near each other in space, and so are likely to be connected by filaments. We then aligned our images of them so that any radio signal from the clusters or the region between them – where we expect the shockwaves to be – would add together. </p>
<p>We first used this method in <a href="https://academic.oup.com/mnras/article/505/3/4178/6273648">a paper published in 2021</a> with data from two radio telescopes: the <a href="https://www.mwatelescope.org/">Murchison Widefield Array</a> in Western Australia and the <a href="https://leo.phys.unm.edu/%7Elwa/index.html">Owens Valley Radio Observatory Long Wavelength Array</a> in New Mexico. These were chosen not only because they covered nearly all the sky but also because they operated at low radio frequencies where this signal is expected to be brighter. </p>
<p>In the first project, we made an exciting discovery: we found a glow between the pairs of clusters! However, because it was an <em>average</em> of many clusters, all containing many galaxies, it was difficult to say for sure the signal was coming from the cosmic magnetic fields, rather than other sources like galaxies. </p>
<h2>A ‘shocking’ revelation</h2>
<p>Normally the magnetic fields in clusters are jumbled up due to turbulence. However, these shock waves force the magnetic fields into order, which means the radio glow they emit is highly <a href="https://www.sciencefocus.com/science/what-is-polarised-light/">polarised</a>. </p>
<p>We decided to try the stacking experiment on maps of polarised radio light. This has the advantage of helping to determine what is causing the signal.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-thread-of-the-cosmic-web-astronomers-spot-a-50-million-light-year-galactic-filament-151569">A thread of the cosmic web: astronomers spot a 50 million light-year galactic filament</a>
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<p>Signals from regular galaxies are only 5% polarised or less, while signals from shockwaves can be 30% polarised or more.</p>
<p>In our <a href="http://www.science.org/doi/10.1126/sciadv.ade7233">new work</a>, we used radio data from the <a href="https://gmims.ok.ubc.ca/">Global Magneto Ionic Medium Survey</a> as well as the <a href="https://www.esa.int/Science_Exploration/Space_Science/Planck/Planck_at_a_glance">Planck</a> satellite to repeat the experiment. These surveys cover almost the entire sky and have both polarised and regular radio maps. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=603&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=603&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=603&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=758&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=758&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509730/original/file-20230213-22-apg2tf.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=758&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Stacking cluster pairs: the two dark spots aligned vertically are the clusters and show depolarisation due to turbulence, while the outer areas and the area between the clusters is highly polarised.</span>
<span class="attribution"><span class="source">Tessa Vernstrom using Planck data</span>, <span class="license">Author provided</span></span>
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<p>We detected very clear rings of polarised light surrounding cluster pairs. This means the centres of the clusters are depolarised, which is expected as they are very turbulent environments. </p>
<p>However, on the edges of the clusters the magnetic fields are put in order thanks to the shockwaves, meaning we see this ring of polarised light. </p>
<p>We also found an excess of highly polarised light between the clusters, much more than you would expect from just galaxies. We can interpret this as light from the shocks in the connecting filaments. This is the first time such emission has been found in this kind of environment. </p>
<p>We compared our results with state-of-the-art cosmological simulations, the first of their kind to predict not just the total signal of the radio emission but the <em>polarised</em> signal as well. Our data agreed very well with these simulations, and by combining them we are able to understand the magnetic field signal left over from the early Universe.</p>
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<iframe src="https://player.vimeo.com/video/798306932" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">Cosmological simulation showing the gas temperature, radio emission from shocks, and magnetic field lines. Credit: F Vazza (Univ Bologna) / D Wittor (Hamburger Sternwarte) / J West (NRC) / ICRAR.</span></figcaption>
</figure>
<p>In future we would like to repeat this detection for different times over the history of the Universe. We still do not know the origin of these cosmic magnetic fields, but further observations like this can help us to figure out where they came from and how they have evolved. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/we-found-some-strange-radio-sources-in-a-distant-galaxy-cluster-theyre-making-us-rethink-what-we-thought-we-knew-187631">We found some strange radio sources in a distant galaxy cluster. They're making us rethink what we thought we knew.</a>
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<img src="https://counter.theconversation.com/content/199785/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tessa Vernstrom works for the International Centre for Radio Astronomy Research at the University of Western Australia and is also affiliated with CSIRO Space & Astronomy.</span></em></p><p class="fine-print"><em><span>Christopher Riseley works for Alma Mater Studiorum - Università di Bologna. He is also affiliated with the Istituto Nazionale di Astrofisica (INAF) and CSIRO Space & Astronomy. He is supported by funding from the European Research Council (ERC) under the ERC Starting Grant 'DRANOEL', number 714245.</span></em></p>Astronomers have detected a radio glow caused by shockwaves in the gigantic filaments between galaxy clusters in the ‘cosmic web’ which pervades the Universe.Tessa Vernstrom, Senior research fellow, The University of Western AustraliaChristopher Riseley, Research Fellow, Università di BolognaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1515692020-12-17T19:06:48Z2020-12-17T19:06:48ZA thread of the cosmic web: astronomers spot a 50 million light-year galactic filament<figure><img src="https://images.theconversation.com/files/375591/original/file-20201217-13-ah4xaj.jpg?ixlib=rb-1.1.0&rect=0%2C2%2C2000%2C1323&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Ray Norris</span>, <span class="license">Author provided</span></span></figcaption></figure><p>At the very largest scale, the Universe consists of a “cosmic web” made of enormous, tenuous filaments of gas stretching between gigantic clumps of matter. Or that’s what our <a href="https://youtu.be/fuRESt-UK8w">best models</a> suggest. All we have seen so far with our telescopes are the stars and galaxies in the clumps of matter. </p>
<p>So is the cosmic web real, or a figment of our models? Can we confirm our models by detecting these faint gaseous filaments directly? </p>
<p>Until recently, these filaments have been elusive. But now a collaboration between Australian radio astronomers and German x-ray astronomers has detected one. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/374712/original/file-20201214-22-1kjf4g4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/374712/original/file-20201214-22-1kjf4g4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374712/original/file-20201214-22-1kjf4g4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374712/original/file-20201214-22-1kjf4g4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374712/original/file-20201214-22-1kjf4g4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374712/original/file-20201214-22-1kjf4g4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374712/original/file-20201214-22-1kjf4g4.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">
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<span class="caption">On the largest scales, matter in the Universe is arranged in a cosmic web consisting of filaments of gas separated by voids, with clusters where the filaments meet each other.</span>
<span class="attribution"><span class="source">From the MAGNETICUM simulation, courtesy of Klaus Dolag, Universitäts-Sternwarte München, Ludwig-Maximilians-Universität München, Germany</span></span>
</figcaption>
</figure>
<p>CSIRO’s newly completed Australian Square Kilometre Array Pathfinder (ASKAP) telescope in Western Australia is <a href="https://theconversation.com/weve-mapped-a-million-previously-undiscovered-galaxies-beyond-the-milky-way-take-the-virtual-tour-here-148442">starting</a> to produce a large-scale picture of the Universe in radio frequencies. This telescope can see deeper than any other radio telescope, producing new discoveries, such as the <a href="https://theconversation.com/wtf-newly-discovered-ghostly-circles-in-the-sky-cant-be-explained-by-current-theories-and-astronomers-are-excited-142812">unexplained Odd Radio Circles or ORCs</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/374387/original/file-20201211-14-q96m9r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/374387/original/file-20201211-14-q96m9r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374387/original/file-20201211-14-q96m9r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374387/original/file-20201211-14-q96m9r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374387/original/file-20201211-14-q96m9r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374387/original/file-20201211-14-q96m9r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374387/original/file-20201211-14-q96m9r.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">CSIRO’s Australian Square Kilometre Array Pathfinder telescope in Western Australia.</span>
<span class="attribution"><span class="source">Ray Norris</span></span>
</figcaption>
</figure>
<h2>Seeing with radio waves and x-rays</h2>
<p>This year has also seen the publication of the first observations by the German eROSITA Space Telescope, which is giving us our deepest large-scale picture of the Universe in x-ray frequencies. Both of these next-generation telescopes have an unprecedented ability to scan large areas of sky at once, so they are beautifully matched to study the large-scale features of the Universe. Together, they can achieve much more than either on its own, so naturally we have joined forces.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/374388/original/file-20201211-15-6ytclt.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/374388/original/file-20201211-15-6ytclt.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374388/original/file-20201211-15-6ytclt.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374388/original/file-20201211-15-6ytclt.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374388/original/file-20201211-15-6ytclt.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374388/original/file-20201211-15-6ytclt.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374388/original/file-20201211-15-6ytclt.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">
<figcaption>
<span class="caption">The seven cameras of the eROSITA Space Telescope, enabling it to image the x-rays from large areas of the sky.</span>
<span class="attribution"><span class="source">Max Planck Institut for Extraterrestrial Physics</span></span>
</figcaption>
</figure>
<p>The first result from this collaboration is the discovery of a cosmic filament of hot gas. This study was led by Thomas Reiprich of the University of Bonn and Marcus Brueggen of the University of Hamburg, and involved Australian scientists from CSIRO and from Curtin, Macquarie, Monash and Western Sydney universities. It is published today in <a href="https://arxiv.org/abs/2012.08775">two</a> <a href="https://arxiv.org/abs/2012.08491">papers</a> in the journal Astronomy and Astrophysics.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/374384/original/file-20201211-20-1312osv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/374384/original/file-20201211-20-1312osv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=646&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374384/original/file-20201211-20-1312osv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=646&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374384/original/file-20201211-20-1312osv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=646&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374384/original/file-20201211-20-1312osv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=811&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374384/original/file-20201211-20-1312osv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=811&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374384/original/file-20201211-20-1312osv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=811&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">eROSITA image showing the clusters at the centre, and the dark green gaseous filament stretching 50 million light-years from the bottom left to the top right.</span>
<span class="attribution"><span class="source">Thomas Reiprich</span></span>
</figcaption>
</figure>
<h2>The cosmic web</h2>
<p>The Big Bang 13.8 billion years ago produced a Universe filled with invisible dark matter, together with a featureless gas of hydrogen and helium, and little else. Over the next few billion years, the gas clumped together under the attraction of gravity, forming filaments of matter with vast empty voids between them. The filaments probably contain more than half the matter in the Universe, even though the filaments themselves contain just ten particles per cubic metre - less than the best vacuum we can create on Earth.</p>
<p>Nearly all the galaxies we see today, including our own Milky Way, are thought to have formed in these filaments. We think galaxies then slide along the filaments until they fall into the dense clusters of galaxies clumped together at junctions where filaments meet. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/374389/original/file-20201211-15-1u4hm61.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/374389/original/file-20201211-15-1u4hm61.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=205&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374389/original/file-20201211-15-1u4hm61.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=205&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374389/original/file-20201211-15-1u4hm61.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=205&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374389/original/file-20201211-15-1u4hm61.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=258&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374389/original/file-20201211-15-1u4hm61.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=258&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374389/original/file-20201211-15-1u4hm61.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=258&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This image, from a simulation called Magneticum, shows clumps moving along filaments, merging with the main systems to form ever larger, denser, and hotter structures. A movie is available at https://astro.uni-bonn.de/~reiprich/A3391_95/ .</span>
<span class="attribution"><span class="source">Thomas Reiprich (link to paper)</span></span>
</figcaption>
</figure>
<p>But until now, all this was hypothetical — we could see the galaxies and clusters, but we couldn’t see the gaseous filaments themselves. Now, eROSITA has directly detected the hot gas in a filament 50 million light-years long. This is an important step forward, confirming our model of the cosmic web is correct.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/weve-mapped-a-million-previously-undiscovered-galaxies-beyond-the-milky-way-take-the-virtual-tour-here-148442">We've mapped a million previously undiscovered galaxies beyond the Milky Way. Take the virtual tour here.</a>
</strong>
</em>
</p>
<hr>
<h2>A smooth ride</h2>
<p>We also expected the hot gas would whip up electrons to produce radio frequency emissions, but, curiously, we don’t detect the filament with ASKAP. This tells us the hot gas is flowing smoothly, without the turbulence that would accelerate electrons to produce radio waves. So the galaxies are getting a smooth ride as they fall into the clusters. </p>
<p>We can see the individual galaxies falling into the clusters in the radio images from ASKAP. At radio wavelengths, we often see galaxies bracketed by a pair of jets, caused by electrons squirting out from near the black hole in the centre of the galaxy. </p>
<p>However, in our radio images of these clusters, we see the jets bent and distorted as they are buffeted by intergalactic winds in the dense gas in the clusters. Again, this is a good confirmation of our models.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/374392/original/file-20201211-20-1uf15tm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/374392/original/file-20201211-20-1uf15tm.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=602&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374392/original/file-20201211-20-1uf15tm.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=602&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374392/original/file-20201211-20-1uf15tm.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=602&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374392/original/file-20201211-20-1uf15tm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=757&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374392/original/file-20201211-20-1uf15tm.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=757&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374392/original/file-20201211-20-1uf15tm.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=757&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">ASKAP radio data (white) overlaid on the eROSITA x-ray image (coloured). The circles show individual radio galaxies. The jets of the radio galaxies, normally straight, are bent into contorted shapes by the intergalactic winds within the clusters.</span>
<span class="attribution"><span class="source">Marcus Brueggen.</span></span>
</figcaption>
</figure>
<p>This work is not only important as confirmation of our model of the Universe, but is also the first result to come from the collaboration between ASKAP and eROSITA. These two telescopes are beautifully matched to survey our Universe, seeing the Universe as it has never been seen before, and I expect this discovery to be the first of many.</p>
<hr>
<p><em>We acknowledge the Wajarri Yamatji people as the traditional owners of the ASKAP Observatory site.</em></p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/wtf-newly-discovered-ghostly-circles-in-the-sky-cant-be-explained-by-current-theories-and-astronomers-are-excited-142812">'WTF?': newly discovered ghostly circles in the sky can't be explained by current theories, and astronomers are excited</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/151569/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ray Norris is affiliated with CSIRO.</span></em></p>A collaboration between Australian and German scientists gives an unrivalled view of the structure of the Universe.Ray Norris, Professor, School of Science, Western Sydney UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1296122020-02-06T21:43:46Z2020-02-06T21:43:46ZNew clues in the search for the oldest galaxies in the universe<figure><img src="https://images.theconversation.com/files/312337/original/file-20200128-81357-gnbpl6.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5325%2C2969&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An enhanced image of galaxy clusters.</span> <span class="attribution"><span class="source">(NASA/Shutterstock)</span></span></figcaption></figure><p>A galaxy cluster can be likened to a great city of galaxies, a galactic conurbation where each galaxy represents an individual, twinkling structure. Just as an archaeologist might seek evidence of the oldest cities on Earth, astronomers have long sought to discover the oldest galaxy clusters in the universe — each the cosmic equivalent of an ancient civilization like Jericho or Ur. </p>
<p>I have been fortunate to lead <a href="https://doi.org/10.1038/s41586-019-1829-4">a team of astronomers in discovering just such an example of an old galaxy cluster</a>. How old? The light from the galaxy cluster, named XLSSC 122 has taken 10.4 billion years to travel across the universe to us.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/309524/original/file-20200111-97183-1tr4hnk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/309524/original/file-20200111-97183-1tr4hnk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/309524/original/file-20200111-97183-1tr4hnk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=601&fit=crop&dpr=1 600w, https://images.theconversation.com/files/309524/original/file-20200111-97183-1tr4hnk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=601&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/309524/original/file-20200111-97183-1tr4hnk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=601&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/309524/original/file-20200111-97183-1tr4hnk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=756&fit=crop&dpr=1 754w, https://images.theconversation.com/files/309524/original/file-20200111-97183-1tr4hnk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=756&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/309524/original/file-20200111-97183-1tr4hnk.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"></a>
<figcaption>
<span class="caption">A composite image of the galaxy cluster XLSSC 122 using images from the Hubble Space Telescope and European Southern Observatory’s Very Large Telescope. The white contours reveal strong X-ray emission captured by the European Space Agency’s X-ray Multi-Mirror satellite.</span>
<span class="attribution"><span class="source">(Jon Willis)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>A youthful universe</h2>
<p>Astronomers believe that <a href="http://doi.org/10.1088/0004-637X/794/2/135">the universe itself is 13.7 billion years old</a>, so a little maths tells us that we are observing XLSSC 122 when the universe was a mere 3.3 billion years old. Imagine our surprise then, when each new view of this galaxy cluster revealed a physical structure seemingly every bit as mature and developed as galaxy clusters in our present-day universe — a situation rather like looking at a photo from your youth in which you appear much older than you were.</p>
<p>XLSSC 122 is a remarkably precocious presence in a youthful universe, a clue perhaps that the universe — at least the densest parts of it — can form stars, accumulate into galaxies and eventually be drawn into galaxy clusters with surprising rapidity. Given that <a href="https://arxiv.org/abs/1111.6590">computer simulations of the assembly of galaxy clusters</a> indicate more gradual growth, the discovery of XLSSC 122 suggests that our current ideas of how structure forms in the universe may be incomplete.</p>
<h2>Discovering galaxy clusters</h2>
<p>When I first saw it, <a href="https://arxiv.org/abs/1212.4185">XLSSC 122 appeared as an unassuming collection of photons on an X-ray image of the sky</a> taken by the <a href="https://sci.esa.int/web/xmm-newton">European Space Agency’s X-ray Multi-Mirror space observatory</a>. Though viewed at great distance, we knew we were potentially observing a hot halo of gas — at 10 million Kelvin — confined within the gravitational field of a massive cluster of galaxies.</p>
<p>However, visible light images taken with the <a href="https://www.cfht.hawaii.edu/">Canada-France-Hawaii Telescope</a> revealed no galaxies associated with the X-ray source. This was an interesting clue that we may have discovered a distant galaxy cluster where the expansion of the universe had shifted the visible light emitted by the cluster galaxies into the infrared. </p>
<p>From this realization, we proceeded to obtain an image of our candidate cluster using the <a href="https://www.eso.org/public/teles-instr/paranal-observatory/vlt/">European Southern Observatory’s Very Large Telescope</a>. This image, taken with an infrared camera, revealed the telltale presence of faint red objects — distant galaxies; but exactly how distant remained a mystery.</p>
<h2>Hubble Space Telescope brings ultimate clarity</h2>
<p>Having compiled a strong case that XLSSC 122 was a distant galaxy cluster, perhaps the most distant, we were awarded observing time with the <a href="https://hubblesite.org/">Hubble Space Telescope</a>. Given that only one out of every 10 Hubble proposals is successful, this represented an achievement in itself.</p>
<p>Although the Hubble telescope is nearly 30 years old, it remains a pre-eminent astronomical facility. Our images of XLSSC 122 appeared sharp and clear compared to the fuzzy images obtained from ground-based observatories. Although I have been a professional astronomer for 20 years, seeing the Hubble images of our cluster represented a near-unique discovery moment. It was immediately clear from the galaxy colours and spectra that XLSSC 122 was supremely distant: <a href="https://www.esa.int/Science_Exploration/Space_Science/What_is_red_shift">it lay at a redshift</a> of two, meaning that the light from XLSSC 122 had taken 10.4 billion years to reach Earth.</p>
<h2>Simulating galaxies</h2>
<p>How does a cluster such as XLSSC 122 fit into our wider picture of how the universe is structured? Computer simulations allow astronomers to <a href="https://www.illustris-project.org/">recreate the uneven distribution of matter in the early universe</a> and then to follow the force of gravity as it draws the more dense regions into massive clusters while less dense regions become ever more sparse. </p>
<p>One can identify clusters in these simulations that have the same properties as XLSSC 122. As a simulation is similar to a movie of the universe, we can fast forward to the present. When we did this for XLSSC 122 we realized that it would become one of the most massive clusters in the universe – comparable to the <a href="https://apod.nasa.gov/apod/ap180326.html">great cluster in Coma</a>, our closest collection of galaxies. The same simulations indicate that XLSSC 122 might only have existed as a cluster of galaxies for perhaps a billion years before the moment we observed it.</p>
<p>Herein lies the mystery. Our study of the starlight from the galaxies that make up XLSSC 122 tells us they are more than one billion years old, perhaps as much as three billion years old. Moreover, they all appeared to start forming stars at almost the same time. But as all of this happened long before these galaxies ever clumped together to form XLSSC 122, we are left with the question as to what caused them to start forming stars in such a synchronized manner in the early universe?</p>
<p>Fortunately, we have a pretty good idea of where to look next. NASA plans to launch the <a href="https://www.jwst.nasa.gov/">James Webb Space Telescope</a> in March 2021, and we are already planning ahead to target XLSSC 122. The Webb telescope will collect approximately six times more light than Hubble and will analyze that light with a number of sensitive instruments. Our aim is to use high-resolution infrared spectroscopy to greatly improve our knowledge of the stellar ages of the galaxies that make up XLSSC 122 and pin down the early life story of this remarkable cluster of galaxies.</p><img src="https://counter.theconversation.com/content/129612/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jon Willis receives funding from the NSERC. </span></em></p>New research using the Hubble Space Telescope reveals that galaxies may be forming at faster rates than previously believed.Jon Willis, Associate professor, Physics and Astronomy, University of VictoriaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1232362019-09-18T15:24:30Z2019-09-18T15:24:30ZSomething is killing galaxies, and scientists are on the case<figure><img src="https://images.theconversation.com/files/292489/original/file-20190914-8661-1mtywm4.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1280%2C1339&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An image taken by the Hubble telescope of NGC 4639, a barred spiral galaxy in the constellation of Virgo. </span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>In the most extreme regions of the universe, galaxies are being killed. Their star formation is being shut down and astronomers want to know why.</p>
<p>The first ever Canadian-led large project on one of the world’s leading telescopes is hoping to do just that. The new program, called the Virgo Environment Traced in Carbon Monoxide survey (VERTICO), is investigating, in brilliant detail, how galaxies are killed by their environment.</p>
<p>As VERTICO’s principal investigator, I lead a team of 30 experts that are using <a href="https://www.almaobservatory.org/en/home/">the Atacama Large Millimeter Array (ALMA)</a> to map the molecular hydrogen gas, <a href="https://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve">the fuel from which new stars are made</a>, at high resolution across 51 galaxies in our nearest galaxy cluster, called the <a href="https://apod.nasa.gov/apod/ap150804.html">Virgo Cluster</a>.</p>
<p>Commissioned in 2013 at a cost of US$1.4 billion, <a href="https://www.almaobservatory.org/en/about-alma-at-first-glance/">ALMA is an array of connected radio dishes at an altitude of 5,000 metres in the Atacama Desert of northern Chile</a>. It is an international partnership between Europe, the United States, Canada, Japan, South Korea, Taiwan and Chile. The largest ground-based astronomical project in existence, ALMA is the most advanced millimetre wavelength telescope ever built and ideal for studying the clouds of dense cold gas from which new stars form, which cannot be seen using visible light.</p>
<p>Large ALMA research programs such as VERTICO are designed to address strategic scientific issues that will lead to a major advance or breakthrough in the field.</p>
<h2>Galaxy clusters</h2>
<p>Where galaxies live in the universe and how they interact with their surroundings (the intergalactic medium that surrounds them) and each other are major influences on their ability to form stars. But precisely how this so-called environment dictates the life and death of galaxies remains a mystery.</p>
<p><a href="https://imagine.gsfc.nasa.gov/science/objects/clusters.html">Galaxy clusters</a> are the most massive and most extreme environments in the universe, containing many hundreds or even thousands of galaxies. Where you have mass, you also have gravity and the huge gravitational forces present in clusters accelerates galaxies to great speeds, often thousands of kilometres-per-second, and superheats the plasma in between galaxies to temperatures so high that it <a href="http://www.mpe.mpg.de/990081/VirgoCluster">glows with X-ray light</a>.</p>
<p>In the dense, inhospitable interiors of these clusters, galaxies interact strongly with their surroundings and with each other. It is these interactions that can kill off — or quench — their star formation.</p>
<p>Understanding which quenching mechanisms shut off star formation and how they do it is main the focus of the VERTICO collaboration’s research.</p>
<h2>The life cycle of galaxies</h2>
<p>As galaxies fall through clusters, the intergalactic plasma can rapidly remove their gas in a violent process called <a href="https://astronomy.swin.edu.au/cosmos/R/Ram+Pressure+Stripping">ram pressure stripping</a>. When you remove the fuel for star formation, you effectively kill the galaxy, turning it into a dead object in which no new stars are formed.</p>
<p>In addition, the high temperature of clusters can stop hot gas cooling and condensing onto galaxies. In this case, the gas in the galaxy isn’t actively removed by the environment but is consumed as it forms stars. This process leads to a slow, inexorable shut down in star formation known, somewhat morbidly, as starvation or strangulation.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/291813/original/file-20190910-190012-11ri2b6.png?ixlib=rb-1.1.0&rect=0%2C0%2C1422%2C1119&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/291813/original/file-20190910-190012-11ri2b6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=473&fit=crop&dpr=1 600w, https://images.theconversation.com/files/291813/original/file-20190910-190012-11ri2b6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=473&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/291813/original/file-20190910-190012-11ri2b6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=473&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/291813/original/file-20190910-190012-11ri2b6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=594&fit=crop&dpr=1 754w, https://images.theconversation.com/files/291813/original/file-20190910-190012-11ri2b6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=594&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/291813/original/file-20190910-190012-11ri2b6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=594&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An image of spiral galaxy NGC 4330 in the Virgo Cluster. Ram pressure stripped hot gas is shown in red and a blue overlay shows star-forming gas.</span>
<span class="attribution"><a class="source" href="https://arxiv.org/abs/1801.09685">Fossatie et al. (2018)</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>While these processes vary considerably, each leaves a unique, identifiable imprint on the galaxy’s star-forming gas. Piecing these imprints together to form a picture of how clusters drive changes in galaxies is a major focus of the VERTICO collaboration. Building on <a href="https://arxiv.org/pdf/0908.3017.pdf">decades of work</a> to provide insight into how environment drives galaxy evolution, we aim to add a critical new piece of the puzzle.</p>
<h2>An ideal case study</h2>
<p>The Virgo Cluster is an ideal location for such a detailed study of environment. It is our nearest massive galaxy cluster and is in the process of forming, which means that we can get a snapshot of galaxies in different stages of their life cycles. This allows us to build up a detailed picture of how star formation is shut off in cluster galaxies. </p>
<p>Galaxies in the Virgo cluster have been observed at almost every wavelength in the electromagnetic spectrum (for example, <a href="http://www.astro.yale.edu/viva/">radio</a>, <a href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/ApJS/215/22">optical</a> and <a href="http://galex.oamp.fr/guvics/">ultra-violet</a> light), but observations of star-forming gas (made at millimetre wavelengths) with the required sensitivity and resolution do not exist yet. As one of the largest galaxy surveys on ALMA to date, VERTICO will provide high resolution maps of molecular hydrogen gas — the raw fuel for star formation — for 51 galaxies. </p>
<p>With ALMA data for this large sample of galaxies, it will be possible to reveal exactly which quenching mechanisms, ram pressure stripping or starvation, are killing galaxies in extreme environments and how.</p>
<p>By mapping the star-forming gas in galaxies that are the smoking gun examples of environment-driven quenching, VERTICO will advance our current understanding of how galaxies evolve in the densest regions of the Universe.</p>
<p>[ <em>Deep knowledge, daily.</em> <a href="https://theconversation.com/ca/newsletters?utm_source=TCCA&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=deepknowledge">Sign up for The Conversation’s newsletter</a>. ]</p><img src="https://counter.theconversation.com/content/123236/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Toby Brown does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The first ever Canadian-led large project on one of the world’s leading telescopes will investigate how the birth and death of galaxies are affected by their environment.Toby Brown, Post Doctorate Fellow in Astrophysics, McMaster UniversityLicensed as Creative Commons – attribution, no derivatives.