tag:theconversation.com,2011:/es/topics/supermassive-black-holes-21021/articlesSupermassive black holes – The Conversation2024-02-27T16:00:16Ztag:theconversation.com,2011:article/2245642024-02-27T16:00:16Z2024-02-27T16:00:16ZA black hole discovery could force us to rethink how galaxies came to be<figure><img src="https://images.theconversation.com/files/578316/original/file-20240227-30-ntlqbc.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3834%2C2155&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://webbtelescope.org/contents/media/images/2021/026/01F8QS893NVRJ6EYF0S46237KP?page=1&Tag=Active%20Galaxies/Quasars">NASA, ESA, Joseph Olmsted (STScI)</a></span></figcaption></figure><p>Peering deep into the infancy of the universe, the European Southern Observatory’s Very Large Telescope (VLT) recently confirmed the discovery of <a href="https://www.nature.com/articles/s41550-024-02195-x">the brightest and fastest growing quasar</a>. Quasars are <a href="https://esahubble.org/wordbank/quasar/">luminous objects in the night sky</a> powered by gas falling into a large black hole at the centre of a galaxy. </p>
<p>The discovery of this record-breaking object was fascinating enough. But another crucial aspect to the announcement is that it raises big questions about galaxy formation in the early universe. In particular, it remains puzzling how this quasar, which existed less than two billion years after the Big Bang, could have grown so large so quickly. Probing this conundrum could even lead to a rethink of how galaxies came to be.</p>
<p>Black holes, the densest objects in the universe, are given this name because their gravitational pull is so incredibly strong that not even light can escape their grasp. How then, can a black hole be the origin of such an intense light source? </p>
<p>Well, in some galaxies, <a href="https://science.nasa.gov/universe/black-holes/">where the black hole is sufficiently large</a>, matter is being drawn in at a ferociously high rate. As it spirals in, violent collisions between gases, dust, and stars result in the emission of huge amounts of light energy. The bigger the black hole, the more violent the collisions and the more light is emitted.</p>
<p>The quasar that was the subject of the latest study, known as J0529-4351, has a mass equivalent to 17 billion suns and is incredibly large. There is a spiralling disk of matter spanning a width of seven light years at the centre of the galaxy and the black hole is growing by accreting (accumulating) this matter. The disk’s width is comparable to the distance between Earth and <a href="https://www.britannica.com/place/Alpha-Centauri">the next nearest star system, Alpha Centauri</a>. </p>
<h2>Hiding in plain sight</h2>
<p>The black hole is growing rapidly by consuming a record-breaking amount of mass, equivalent to one sun each day. This intense accretion of matter releases an amount of radiative energy that’s equivalent to a quadrillion (thousand trillion) suns. </p>
<p>This raises the question of why an object so bright has only just been identified in the night sky, despite decades of astronomical observations. It turns out that this sneaky quasar had been hiding in plain sight.</p>
<p>Despite its astonishing luminosity, J0529-4351 is very distant, meaning that it seamlessly blends in among a sea of dimmer stars that lie much closer to Earth. In fact, this quasar is so far away that the light it emits takes a whopping 12 billion years to reach us here on Earth. </p>
<p>The age of the universe is around 13.7 billion years. So this quasar existed just 1.7 billion years after the <a href="https://science.nasa.gov/universe/the-big-bang/">Big Bang, at the beginning of the Universe</a>. </p>
<p>The universe’s expansion following the Big Bang is what permits us to measure the distance to, and therefore the age of, this quasar. A long-known simple <a href="https://www.bbc.co.uk/bitesize/guides/zphppv4/revision/3">formula called Hubble’s law</a>, states that knowing the velocity that an object is moving away from us allows us to calculate how far away it is.</p>
<figure class="align-center ">
<img alt="Very Large Telescope" src="https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The object was confirmed using the Very Large Telescope facility in Chile.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/cerro-paranal-atacama-desert-chile-jan-750390019">Framalicious / Shutterstock</a></span>
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<p>The collisions that occur as matter spirals into this quasar’s black hole raise it to scorching temperatures of 10,000°C. Under these conditions, the atoms in the system emit a characteristic spectrum of light. </p>
<p>These discrete frequencies of light form a sort of barcode that astronomers can use to identify the elemental compositions of objects in the night sky. As an object that’s emitting light moves away from us, the frequency of that observed light undergoes a shift, much like how the sound frequency of an ambulance siren shifts depending on whether it is driving towards or away from you. </p>
<p>This shift seen in astronomical objects is <a href="http://csep10.phys.utk.edu/OJTA2dev/ojta/c2c/galaxies/expanding/lookback_tl.html">known as redshift</a>. This, along with Hubble’s Law, has permitted both the age and the distance (both these properties are linked in cosmology) of J0529-4351 to be confirmed.</p>
<p>This bright beacon from the early universe has raised an important question that is baffling astronomers: how could this black hole, in such a relatively short period of time, grow so fast into such a massive object? Under well accepted models of the early universe, it should have taken longer for it to grow to this size. </p>
<p>What’s more, by tuning the artificial intelligence (AI) models used to scan telescope data for these unusual objects, more could still be found in the coming years. If they resemble J0529-4351, physicists would need to seriously rethink their models of the early universe and galaxy formation.</p>
<p>The fastest-growing black hole ever observed will be the perfect target for a system <a href="https://www.mpe.mpg.de/ir/gravityplus">called Gravity+</a>, an upcoming upgrade to an instrument on the Very Large Telescope called an interferometer. This interferometer is an ingenious way of combining data from the four separate telescopes that actually make up the VLT. </p>
<p>Gravity+ is designed to accurately measure the rotational speed and mass of black holes directly, especially those that lie far away from the Earth. </p>
<p>Furthermore, <a href="https://elt.eso.org/">the European Southern Observatory’s’s Extremely Large Telescope</a>, a 39-metre diameter reflecting telescope, is currently under construction in the Chilean Atacama Desert. This is designed for detecting the optical and near-infrared wavelengths characteristic of distant quasars and will make identifying and characterising such elusive objects even more likely in the future.</p><img src="https://counter.theconversation.com/content/224564/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robin Smith does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The discovery raises big questions about widely accepted models of galaxy formation.Robin Smith, Senior Lecturer in Physics, Sheffield Hallam UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2226122024-02-19T19:04:43Z2024-02-19T19:04:43ZThe brightest object in the universe is a black hole that eats a star a day<figure><img src="https://images.theconversation.com/files/573001/original/file-20240202-23-movrvv.jpg?ixlib=rb-1.1.0&rect=0%2C862%2C2000%2C1967&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Cristy Roberts/ANU</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Scientists have no reported evidence of the true conditions in Hell, perhaps because no one has ever returned to tell the tale. Hell has been imagined as a supremely uncomfortable place, hot and hostile to bodily forms of human life. </p>
<p>Thanks to a huge astronomical survey of the entire sky, we have now found what may be the most hellish place in the universe.</p>
<p>In <a href="https://www.nature.com/articles/s41550-024-02195-x">a new paper in Nature Astronomy</a>, we describe a black hole surrounded by the largest and brightest disc of captive matter ever discovered. The object, called J0529-4351, is therefore also the brightest object found so far in the universe.</p>
<h2>Supermassive black holes</h2>
<p>Astronomers have already found around one million fast-growing supermassive black holes across the universe, the kind that sit at the centres of galaxies and are as massive as millions or billions of Suns. </p>
<p>To grow rapidly, they pull stars and gas clouds out of stable orbits and drag them into a ring of orbiting material called an accretion disc. Once there, very little material escapes; the disc is a mere holding pattern for material that will soon be devoured by the black hole.</p>
<p>The disc is heated by friction as the material in it rubs together. Pack in enough material and the glow of the heat gets so bright that it outshines thousands of galaxies and makes the black hole’s feeding frenzy visible to us on Earth, more than 12 billion light years away.</p>
<h2>The fastest-growing black hole in the universe</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/576335/original/file-20240218-22-6pj8yt.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A somewhat noisy photo of a bright white disk and small reddish dot against a dark background." src="https://images.theconversation.com/files/576335/original/file-20240218-22-6pj8yt.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/576335/original/file-20240218-22-6pj8yt.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=599&fit=crop&dpr=1 600w, https://images.theconversation.com/files/576335/original/file-20240218-22-6pj8yt.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=599&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/576335/original/file-20240218-22-6pj8yt.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=599&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/576335/original/file-20240218-22-6pj8yt.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=753&fit=crop&dpr=1 754w, https://images.theconversation.com/files/576335/original/file-20240218-22-6pj8yt.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=753&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/576335/original/file-20240218-22-6pj8yt.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=753&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 brightest thing in the universe: J0529-4351 is a glowing disc of matter around a supermassive black hole, and it is 500 trillion times brighter than the Sun. (The red dot is a neighbouring star.)</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/s41550-024-02195-x">Dark Energy Camera Legacy Survey DR10 / Nature Astronomy</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The accretion disc of J0529-4351 emits light that is 500 trillion times more intense than that of our Sun. Such a staggering amount of energy can only be released if the black hole eats about a Sun worth of material every day. </p>
<p>It must also have a large mass already. Our data indicate J0529-4351 is 15 to 20 billion times the mass of our Sun.</p>
<p>There is no need to be afraid of such black holes. The light from this monster has taken more than 12 billion years to reach us, which means it would have stopped growing long ago.</p>
<p>In the nearby universe, we see that supermassive black holes these days are mostly sleeping giants. </p>
<h2>Black holes losing their grip</h2>
<p>The age of the black hole feeding frenzy is over because the gas floating around in galaxies has mostly been turned into stars. And after billions of years the stars have sorted themselves into orderly patterns: they are mostly on long, neat orbits around the black holes that sleep in the cores of their galaxies. </p>
<p>Even if a star dove suddenly down towards the black hole, it would most likely carry out a slingshot manoeuvre and escape again in a different direction. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-do-black-holes-twinkle-we-studied-5-000-star-eating-behemoths-to-find-out-198996">Why do black holes twinkle? We studied 5,000 star-eating behemoths to find out</a>
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<p>Space probes use slingshot manoeuvres like this to get a boost from Jupiter to access hard-to-reach parts of the Solar System. But imagine if space were more crowded, and our probe ran into one coming the other way: the two would crash together and explode into a cloud of debris that would rapidly fall into Jupiter’s atmosphere. </p>
<p>Such collisions between stars were commonplace in the disorder of the young universe, and black holes were the early beneficiaries of the chaos.</p>
<h2>Accretion discs – a no-go zone for space travellers</h2>
<p>Accretion discs are gateways to a place whence nothing returns, but they are also profoundly unfriendly to life in themselves. They are like giant storm cells, whose clouds glow at temperatures reaching several tens of thousands of degrees Celsius. </p>
<p>The clouds are moving faster and faster as we get closer to the hole, and speeds can reach 100,000 kilometres per second. They move as far in a second as the Earth moves in an hour.</p>
<p>The disc around J0529-4351 is seven light years across. That is one and a half times the distance from the Sun to its nearest neighbour, Alpha Centauri.</p>
<h2>Why only now?</h2>
<p>If this is the brightest thing in the universe, why has it only been spotted now? In short, it’s because the universe is full of glowing black holes.</p>
<p>The world’s telescopes produce so much data that astronomers use sophisticated machine learning tools to sift through it all. Machine learning, by its nature, tends to find things that are similar to what has been found before.</p>
<p>This makes machine learning excellent at finding run-of-the-mill accretion discs around black holes – roughly a million have been detected so far – but not so good at spotting rare outliers like J0529-4351. In 2015, a Chinese team almost missed a <a href="https://www.nature.com/articles/nature14241">remarkably fast-growing black hole</a> picked out by an algorithm because it seemed too extreme to be real.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/astronomers-see-ancient-galaxies-flickering-in-slow-motion-due-to-expanding-space-208621">Astronomers see ancient galaxies flickering in slow motion due to expanding space</a>
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<p>In our recent work, we were aiming to find all the most extreme objects, the most luminous and most rapidly growing black holes, so we avoided using machine learning tools that were guided by too much prior knowledge. Instead we used more old-fashioned methods to search through new data covering the entire sky, with excellent results.</p>
<p>Our work also depended on Australia’s current 10-year partnership with the European Southern Observatory, an organisation funded by several European countries with a huge array of astronomical facilities.</p><img src="https://counter.theconversation.com/content/222612/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christian Wolf has received funding from the Australian Research Council. </span></em></p>The black hole J0529-4351 is 500 trillion times brighter than the Sun.Christian Wolf, Associate Professor, Astronomy & Astrophysics, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2172412023-12-18T13:23:27Z2023-12-18T13:23:27ZWhy are some black holes bigger than others? An astronomer explains how these celestial vacuums grow<figure><img src="https://images.theconversation.com/files/562536/original/file-20231129-23-ug9ynd.jpg?ixlib=rb-1.1.0&rect=5%2C15%2C3429%2C2863&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Black holes use gravity to pull matter into them. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/HungryBlackHole/4cd9b7c1c318427ba2f3b78c77cfe6de/photo?Query=black%20hole&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=418&currentItemNo=7&vs=true&vs=true">NASA/Chandra X-ray Observatory/M.Weiss via AP</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why are there small and big black holes? Also, why are some black holes invisible and others have white outlines? – Sedra and Humaid, Abu Dhabi, United Arab Emirates</strong></p>
</blockquote>
<hr>
<p><a href="https://theconversation.com/the-scariest-things-in-the-universe-are-black-holes-and-here-are-3-reasons-148615">Black holes</a> are dense astronomical objects with gravity so strong that nothing, not even light, can escape. Anything that crosses the boundary of a black hole’s gravitational influence, called the event horizon, will fall into the black hole. Inside this deep, dense pit, it is never to be seen again. </p>
<p>Black holes litter the universe. Some smaller black holes are sprinkled randomly throughout galaxies like our Milky Way. Other gigantic ones, called <a href="https://theconversation.com/supermassive-black-hole-at-the-center-of-our-galaxy-may-have-a-friend-128295">“supermassive” black holes</a>, lie at the centers of galaxies. Those can weigh anywhere between a million to a billion times the mass of our Sun. So you might be wondering: How can astronomers possibly see something so dark and so big?</p>
<p>I am an <a href="https://jackiechampagne.com">astronomer</a> who studies the very first supermassive black holes that formed in our universe. I want to understand how black holes form and what kinds of astrophysical neighborhoods they grow up in.</p>
<h2>Types of black holes</h2>
<p>Let’s talk about how black holes begin their lives. Two famous scientists, <a href="https://www.britannica.com/biography/Albert-Einstein">Albert Einstein</a> and <a href="https://www.britannica.com/biography/Karl-Schwarzschild">Karl Schwarzchild</a>, first pitched the <a href="https://www.astronomy.com/science/a-brief-history-of-black-holes/">idea of a black hole</a>. They thought that when a large star dies, its core might shrink and shrink until it <a href="https://universe.nasa.gov/black-holes/types/">collapses under its own weight</a>. This is what we astronomers call a “<a href="https://www.nasa.gov/image-article/stellar-mass-black-hole/">stellar mass black hole</a>,” which is just another way of saying it’s comparatively very small.</p>
<p>Stellar mass black holes are only a few times bigger than our Sun. Supermassive black holes are more of a mystery, though. They are many millions of times heavier than our Sun, and they are packed into a small area that’s about the size of our solar system. Some scientists think supermassive black holes might form by <a href="https://science.nasa.gov/astrophysics/focus-areas/black-holes/">many stars colliding and collapsing at once</a>, while others think they might have already started growing several billion years ago. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/tMax0KgyZZU?wmode=transparent&start=13" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Stars at the center of the Milky Way are orbiting around an invisible object, a supermassive black hole, like planets orbit around the Sun. Credit: Andrea Ghez/UCLA/W.M. Keck Observatory.</span></figcaption>
</figure>
<h2>Growing black holes</h2>
<p>What do black holes look like? Most of the time, they are not actively growing, so they are invisible. But we can tell they’re there because <a href="https://theconversation.com/2020-nobel-prize-in-physics-awarded-for-work-on-black-holes-an-astrophysicist-explains-the-trailblazing-discoveries-147614">stars can still orbit around them</a>, just like Earth around the Sun. </p>
<p>When something is orbiting an invisible object at high speeds, scientists know there <a href="https://theconversation.com/2020-nobel-prize-in-physics-awarded-for-work-on-black-holes-an-astrophysicist-explains-the-trailblazing-discoveries-147614">must be a massive black hole</a> in the middle. This is the case for the closest supermassive black hole to us, which lies at the center of the Milky Way – safely millions of miles away from you.</p>
<p>Meanwhile, when a hungry black hole is eating up gas in a galaxy, it heats that gas up until you can see a <a href="https://universe.nasa.gov/black-holes/anatomy/">glowing ring</a> of X-rays, optical light and infrared light around the black hole. Once it exhausts all of the fuel near the event horizon, the light dies down once again and it becomes invisible. </p>
<h2>Outlines around black holes</h2>
<p>One of the most famous “white outlines” is the <a href="https://cerncourier.com/a/building-gargantua/">image of a black hole</a> from <a href="https://www.imdb.com/title/tt0816692/">the movie “Interstellar</a>.” In that movie, they were trying to show the white-hot, glowing ring of gases that are falling into the actively growing black hole. </p>
<p>In real life, we don’t get such a close-up view. The best image of the ring around a real black hole comes from the <a href="https://eventhorizontelescope.org/">Event Horizon Telescope</a>, showing scientists the supermassive black hole at the center of a <a href="https://science.nasa.gov/resource/first-image-of-a-black-hole/">galaxy called M87</a>. It might look blurry to you, but this doughnut is actually the sharpest image ever taken of something so far away.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A blurry golden circle against a black background." src="https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=439&fit=crop&dpr=1 754w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=439&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=439&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 first-ever image of a black hole was taken by the Event Horizon Telescope in 2019. You can see the light as it bends around the intense gravity of the black hole at the center of a galaxy called M87. It might look blurry, but this is the equivalent of being able to read a newspaper on a table in Paris if you were standing in New York.</span>
<span class="attribution"><a class="source" href="https://eventhorizontelescope.org/press-release-april-10-2019-astronomers-capture-first-image-black-hole">Event Horizon Telescope</a></span>
</figcaption>
</figure>
<p>There are lots of types of black holes out there in the universe. Some are small and invisible, and some grow to gigantic proportions by eating up stuff inside a galaxy and shining bright. But don’t worry, black holes can’t just keep sucking in everything in the universe – eventually there is nothing close enough to the black hole to fall in, and it will become invisible again. So you are safe to keep asking questions about black holes. </p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/217241/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. </span></em></p>Pictures of black holes have a white outline around them when photographed, due to one of black holes’ unique and key features.Jaclyn Champagne, JASPER Postdoctoral Researcher, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2192052023-12-06T00:53:30Z2023-12-06T00:53:30ZAstronomers finally caught radio waves from 40 large galaxies in the nearby universe<figure><img src="https://images.theconversation.com/files/563537/original/file-20231205-21-lmh6mq.jpg?ixlib=rb-1.1.0&rect=14%2C0%2C3196%2C2153&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Australian Square Kilometre Array Pathfinder in the Western Australian desert.</span> <span class="attribution"><a class="source" href="https://www.atnf.csiro.au/projects/askap/gallery.html">CSIRO</a></span></figcaption></figure><p>Supermassive black holes reside in some of the biggest galaxies in the universe. They tend to be billions of times more massive that our Sun, and not even light itself can escape a black hole once it gets too close.</p>
<p>But it’s not all darkness. Supermassive black holes power some of the most luminous celestial objects in the universe – active galactic nuclei, which shine across the spectrum of light, including radio waves. </p>
<p>The active galactic nucleus in nearby galaxy Messier 87 is a prodigious emitter of radio waves, 27 orders of magnitude more powerful than the <a href="https://en.wikipedia.org/wiki/Eglin_AFB_Site_C-6">most powerful radio transmitters on Earth</a>.</p>
<p>But not all galaxies blast radio waves like Messier 87. Some very massive nearby galaxies have gone undetected in the radio spectrum despite containing supermassive black holes. Are they switched on in the radio at all, or are they – and therefore their black holes – totally silent?</p>
<p>To find out, we searched for radio waves from the most massive galaxies in the nearby universe, with our results now accepted for publication <a href="https://ui.adsabs.harvard.edu/abs/2023arXiv231115456B/abstract">in the Publications of the Astronomical Society of Australia</a>.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/563524/original/file-20231205-15-zu7j1t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A red and orange donut shape on a black background" src="https://images.theconversation.com/files/563524/original/file-20231205-15-zu7j1t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/563524/original/file-20231205-15-zu7j1t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=532&fit=crop&dpr=1 600w, https://images.theconversation.com/files/563524/original/file-20231205-15-zu7j1t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=532&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/563524/original/file-20231205-15-zu7j1t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=532&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/563524/original/file-20231205-15-zu7j1t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=668&fit=crop&dpr=1 754w, https://images.theconversation.com/files/563524/original/file-20231205-15-zu7j1t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=668&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/563524/original/file-20231205-15-zu7j1t.jpg?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 black hole in Messier 87 is the engine for a powerful radio source.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/news/black-hole-image-makes-history">Event Horizon Telescope Collaboration</a></span>
</figcaption>
</figure>
<h2>A big engine</h2>
<p>It may seem odd that black holes can power anything. After all, no matter – not even light – can escape a black hole. But a lot can happen before the point of no return, known as the event horizon.</p>
<p>As matter falls towards the black hole, it picks up tremendous speed. Particles can end up travelling close to the speed of light, and when particles smash at that speed, they can release a staggering amount of energy. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-do-black-holes-pull-in-light-208848">Curious Kids: how do black holes pull in light?</a>
</strong>
</em>
</p>
<hr>
<p>Several percent of the mass that falls towards a black
hole – “feeds” it – can get <a href="https://ui.adsabs.harvard.edu/abs/2017ApJ...836L...1T/abstract">released as light</a>. Feed a black hole, and it can be a big engine that blasts out radio waves. </p>
<p>So, supermassive black holes are in all the biggest galaxies, but are they always being fed? That question motivated our study. To listen for radio waves from these enormous objects, we used the ASKAP radio telescope in Western Australia, owned and operated by CSIRO – Australia’s national science agency.</p>
<h2>Tuning in on the radio</h2>
<p>Way back in the 1940s, astronomers started detecting radio waves from some massive galaxies using the first radio telescopes. This includes galaxies familiar to amateur astronomers, including Messier 87 in the Virgo constellation and NGC 5128 in Centaurus. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/563531/original/file-20231205-29-9eemqo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Black and white image of silhouettes of two people standing on a clifftop next to an antenna" src="https://images.theconversation.com/files/563531/original/file-20231205-29-9eemqo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/563531/original/file-20231205-29-9eemqo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=601&fit=crop&dpr=1 600w, https://images.theconversation.com/files/563531/original/file-20231205-29-9eemqo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=601&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/563531/original/file-20231205-29-9eemqo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=601&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/563531/original/file-20231205-29-9eemqo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=755&fit=crop&dpr=1 754w, https://images.theconversation.com/files/563531/original/file-20231205-29-9eemqo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=755&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/563531/original/file-20231205-29-9eemqo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=755&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Very powerful celestial sources of radio waves were detected back in the 1940s, thanks to radio telescopes like this one at Dover Heights, Sydney.</span>
<span class="attribution"><span class="source">CSIRO Radio Astronomy Image Archive</span></span>
</figcaption>
</figure>
<p>As technology advanced, more very massive galaxies were detected in radio waves. In the early 2000s, astronomers found that about <a href="https://doi.org/10.1111/j.1365-2966.2007.11937.x">a third of very massive galaxies</a> in the Sloan Digital Sky Survey were detectable in the radio data from the Very Large Array, located in New Mexico. </p>
<p>A decade ago, <a href="https://ui.adsabs.harvard.edu/abs/2011ApJ...731L..41B/abstract">our team also used data</a> from the Very Large Array to search for radio emissions from the most massive nearby galaxies. Some were easily detected while others were indistinguishable from noise. </p>
<p>However, there was a strong hint. While the radio signals from the most massive galaxies were sometimes not distinguishable from noise individually, we always found a positive signal. </p>
<p>If some galaxies were not emitting radio waves, we would expect random noise to produce a mix of positive and negative signals. Getting a positive signal every time suggested all massive galaxies are radio sources. But digging into the noise left us unsure, until now.</p>
<h2>New telescopes and a new view</h2>
<p>There have been major advances in radio telescopes during the past decade, both in radio receivers and computing power. New radio telescopes include the ASKAP radio telescope and the Murchison Widefield Array, both located at Inyarrimanha Ilgari Bundara, CSIRO’s Murchison Radio-astronomy Observatory on Wajarri Yamaji country in Western Australia. There is also the <a href="https://www.astron.nl/telescopes/lofar/">Low Frequency Array</a> (Lofar) in Europe.</p>
<p>These telescopes can survey the sky with greater sensitivity and speed than the previous generation of radio telescopes. For example, <a href="https://research.csiro.au/racs/home/survey/">the Rapid ASKAP Continuum Survey</a> is just a preliminary radio survey of 83% of the entire sky, but is already three times more sensitive than comparable surveys with the previous generation of radio telescopes.</p>
<p>For our new study, we no longer needed to look for mere hints of the noise. We detected radio waves from all 40 of the most massive galaxies in our survey area.</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>
</strong>
</em>
</p>
<hr>
<h2>Dialled up and down</h2>
<p>So, it now looks like all very massive galaxies are emitting radio waves, but are all of their black holes being fed? Most are, but probably not all.</p>
<p><a href="https://ui.adsabs.harvard.edu/abs/2022A%26A...660A..93C/abstract">Studies with Lofar</a> suggest some radio sources in massive galaxies are afterglows from earlier activity. It is likely these are temporary pauses, and these black holes will fire up again. </p>
<p>Another piece of the puzzle is the radio power. Two galaxies of the same mass can differ in radio power by a factor of 10,000. Why does this happen?</p>
<p>We don’t know the answer yet, but there are some clues. Our work and <a href="https://ui.adsabs.harvard.edu/abs/2023A%26A...673A..12Z/abstract">a recent study with Lofar</a> find that, on average, the galaxies that rotate the least are the strongest radio wave emitters. Some of the exceptions to this trend are curious, with evidence of mergers with other galaxies. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/563526/original/file-20231205-19-f7uav3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A star field with several galaxies of different shapes visible in the centre" src="https://images.theconversation.com/files/563526/original/file-20231205-19-f7uav3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/563526/original/file-20231205-19-f7uav3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=445&fit=crop&dpr=1 600w, https://images.theconversation.com/files/563526/original/file-20231205-19-f7uav3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=445&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/563526/original/file-20231205-19-f7uav3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=445&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/563526/original/file-20231205-19-f7uav3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=559&fit=crop&dpr=1 754w, https://images.theconversation.com/files/563526/original/file-20231205-19-f7uav3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=559&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/563526/original/file-20231205-19-f7uav3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=559&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Galaxy NGC 6876 emits radio waves, but is thousands of times fainter than Messier 87.</span>
<span class="attribution"><span class="source">Legacy Imaging Surveys/D. Lang (Perimeter Institute)</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>There is much to learn about very massive galaxies and their black holes, but data from the new generation of radio telescopes has revealed a great deal. </p>
<p>All very massive galaxies emit radio waves, but their power varies. Determining how all this works will be a challenge, but there are clues for astronomers to now follow.</p><img src="https://counter.theconversation.com/content/219205/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.</span></em></p>Do all big black holes in very massive galaxies emit radio waves? We used the latest radio telescopes to find out.Michael J. I. Brown, Associate Professor in Astronomy, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag: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/2084842023-06-29T00:13:09Z2023-06-29T00:13:09ZUsing a detector the size of a galaxy, astronomers find strongest evidence yet for gravitational waves from supermassive black hole pairs<figure><img src="https://images.theconversation.com/files/534245/original/file-20230627-24-e1bn10.png?ixlib=rb-1.1.0&rect=0%2C10%2C3456%2C1929&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">OzGrav / Swinburne / Carl Knox</span></span></figcaption></figure><p>When black holes and other enormously massive, dense objects whirl around one another, they send out ripples in space and time called <a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">gravitational waves</a>. These waves are one of the few ways we have to study the enigmatic cosmic giants that create them.</p>
<p>Astronomers have observed the high-frequency “chirps” of colliding black holes, but the ultra-low-frequency rumble of supermassive black holes orbiting one another has proven harder to detect. For decades, we have been observing <a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">pulsars</a>, a type of star that pulses like a lighthouse, in search of the faint rippling of these waves.</p>
<p>Today, pulsar research collaborations around the world – including ours, the <a href="https://www.atnf.csiro.au/research/pulsar/ppta/">Parkes Pulsar Timing Array</a> – announced their <a href="https://doi.org/10.3847/2041-8213/acdd02">strongest evidence yet</a> for the existence of these waves.</p>
<h2>What are gravitational waves?</h2>
<p>In 1915, German-born physicist Albert Einstein presented a breakthrough insight into the nature of <a href="https://theconversation.com/explainer-gravity-5256">gravity</a>: the general theory of relativity.</p>
<p>The theory describes the Universe as a four-dimensional “fabric” called spacetime that can stretch, squeeze, bend and twist. Massive objects distort this fabric to give rise to gravity.</p>
<p>A curious consequence of the theory is that the motion of massive objects should produce ripples in this fabric, called gravitational waves, which spread at the speed of light.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-gravity-5256">Explainer: gravity</a>
</strong>
</em>
</p>
<hr>
<p>It takes an enormous amount of energy to create the tiniest of these ripples. For this reason, Einstein was convinced gravitational waves would never be directly observed. </p>
<p>A century later, researchers from the LIGO and Virgo collaborations witnessed the <a href="https://theconversation.com/gravitational-waves-discovered-top-scientists-respond-53956">collision of two black holes</a>, which sent a burst of gravitational waves <a href="https://theconversation.com/explainer-why-you-can-hear-gravitational-waves-when-things-collide-in-the-universe-92356">chirping</a> throughout the Universe.</p>
<p>Now, seven years after this discovery, radio astronomers from Australia, China, Europe, India, and North America have found evidence for ultra-low-frequency gravitational waves.</p>
<h2>A slow rumbling of gravitational waves</h2>
<p>Unlike the sudden burst of gravitational waves reported in 2016, these ultra-low-frequency gravitational waves take years or even decades to oscillate. </p>
<p>They are expected to be produced by <a href="https://theconversation.com/when-galaxies-collide-the-growth-of-supermassive-black-holes-19321">pairs of supermassive black holes</a>, orbiting at the cores of distant galaxies throughout the Universe. To find these gravitational waves, scientists would need to construct a detector the size of a galaxy. </p>
<figure class="align-center ">
<img alt="An illustration showing Earth, pulsars, and gravitational waves." src="https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=441&fit=crop&dpr=1 600w, https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=441&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=441&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=554&fit=crop&dpr=1 754w, https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=554&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/533985/original/file-20230626-17-adsv86.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=554&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">As gravitational waves warp spacetime around Earth, they distort the arrival times of radio waves from distant pulsars.</span>
<span class="attribution"><span class="source">OzGrav / Swinburne / Carl Knox</span></span>
</figcaption>
</figure>
<p>Or we can use pulsars, which are already spread across the galaxy, and whose pulses arrive at our telescopes with the regularity of precise clocks.</p>
<p>CSIRO’s Parkes radio telescope, <a href="https://blog.csiro.au/parkes-telescope-indigenous-name/">Murriyang</a>, has been observing an array of these pulsars for almost two decades. Our <a href="https://www.atnf.csiro.au/research/pulsar/ppta/">Parkes Pulsar Timing Array</a> team is one of several collaborations around the world that have <a href="https://doi.org/10.3847/2041-8213/acdd02">today announced</a> hints of gravitational waves in their latest data sets. </p>
<p>Other collaborations in China (CPTA), Europe and India (EPTA and InPTA), and North America (NANOGrav) see similar signals.</p>
<p>The signal we are searching for is a random “ocean” of gravitational waves produced by all the pairs of supermassive black holes in the Universe. </p>
<p>Observing these waves is not only another triumph of Einstein’s theory, but has important consequences for our understanding of the history of galaxies in the Universe. Supermassive black holes are the engines at the heart of galaxies that feed on gas and regulate star formation.</p>
<p>The signal appears as a low-frequency rumble, common to all pulsars in the array. As the gravitational waves wash over Earth, they affect the apparent rotation rates of the pulsars.</p>
<p>The stretching and squeezing of our galaxy by these waves ultimately changes the distances to the pulsars by just tens of metres. That’s not much when the pulsars are typically about 1,000 light-years away (that’s about 10,000,000,000,000,000,000 metres).</p>
<p>Remarkably, we can observe these shifts in spacetime as nanosecond delays to the pulses, which radio astronomers can track with relative ease because pulsars are such stable natural clocks.</p>
<h2>What has been announced?</h2>
<p>Because the ultra-low-frequency gravitational waves take years to oscillate, the signal is expected to emerge slowly. </p>
<p>First, radio astronomers observed a <a href="https://doi.org/10.3847/2041-8213/abd401">common rumble</a> in the pulsars, but its origin was unknown. </p>
<p>Now, the unique fingerprint of gravitational waves is beginning to appear as an attribute of this signal, observed by each of the pulsar timing array collaborations around the world. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/when-galaxies-collide-the-growth-of-supermassive-black-holes-19321">When galaxies collide: the growth of supermassive black holes</a>
</strong>
</em>
</p>
<hr>
<p>This fingerprint describes a particular relationship between the similarity of pulse delays and the separation angle between pulsar pairs on the sky. </p>
<p>The relationship arises because spacetime at Earth is stretched, changing the distances to pulsars in a way that depends on their direction. Pulsars close together in the sky show a more similar signal than pulsars separated at right angles, for example.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534513/original/file-20230628-23-bgtedj.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">CSIRO’s Parkes radio telescope, Murriyang.</span>
<span class="attribution"><span class="source">CSIRO / A. Cherney</span></span>
</figcaption>
</figure>
<p>The breakthrough has been enabled by improved technology at our observatories. The Parkes Pulsar Timing Array has the longest high-quality data set, thanks to the advanced receiver and signal processing technology installed on Murriyang. This technology has enabled the telescope to discover many of the best pulsars used by collaborations around the globe for the gravitational wave searches.</p>
<p>Earlier results from our collaboration and others showed the signal expected from gravitational waves <a href="https://theconversation.com/where-are-the-missing-gravitational-waves-47940">was missing from pulsar observations</a>. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/where-are-the-missing-gravitational-waves-47940">Where are the missing gravitational waves?</a>
</strong>
</em>
</p>
<hr>
<p>Now, we seem to be seeing the signal with relative clarity. By segmenting our long data set into shorter “time-slices”, we show the signal appears to be growing with time. The underlying cause of this observation is unknown, but it may be that the gravitational waves are behaving unexpectedly.</p>
<p>The new evidence for ultra-low-frequency gravitational waves is exciting for astronomers. To confirm these signatures, the global collaborations will need to combine their data sets, which increases their sensitivity to gravitational waves many-fold. </p>
<p>Efforts to produce this combined data set are now in progress under the <a href="https://ipta4gw.org/">International Pulsar Timing Array</a> project, whose members met in Port Douglas in Far North Queensland last week. Future observatories, like the Square Kilometre Array under construction in Australia and South Africa, will turn these studies into a rich source of knowledge about the history of our Universe.</p><img src="https://counter.theconversation.com/content/208484/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>By timing radio pulses from an array of galactic pulsars, scientists see hints of gravitational waves from supermassive black hole pairs in a breakthrough that may reveal hidden details of galaxy evolution.Daniel Reardon, Postdoctoral researcher in pulsar timing and gravitational waves, Swinburne University of TechnologyAndrew Zic, Research scientist, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1998312023-02-15T17:16:17Z2023-02-15T17:16:17ZBlack holes may be the source of mysterious dark energy that makes up most of the universe<figure><img src="https://images.theconversation.com/files/509870/original/file-20230213-4443-xsmxpu.jpg?ixlib=rb-1.1.0&rect=313%2C0%2C2251%2C1483&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">black hole</span> </figcaption></figure><p><a href="https://www.nasa.gov/vision/universe/starsgalaxies/black_hole_description.html">Black holes</a> could explain a mysterious form of energy that makes up most of the universe, according to astronomers. The existence of <a href="https://en.wikipedia.org/wiki/Dark_energy">“dark energy”</a> has been inferred from observations of stars and galaxies, but no one has been able to explain what it is, or where it comes from.</p>
<p>The stuff, or matter, that makes up the familiar world around us is just 5% of everything in the universe. Another 27% is <a href="https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy">dark matter</a>, a shadowy counterpart of ordinary matter which does not emit, reflect or absorb light. However, the majority of the cosmos – around 68% – is dark energy.</p>
<p>The new evidence that black holes could be the source of dark energy is described in <a href="https://iopscience.iop.org/article/10.3847/2041-8213/acb704">a scientific paper</a> published in The Astrophysical Journal Letters. The study is the work of 17 astronomers in nine countries and was led by the University of Hawaii. The collaboration included researchers in the UK, based at STFC RAL Space, The Open University, and Imperial College London.</p>
<p>Searching through data spanning nine billion years of cosmic history, the astronomers have uncovered the first evidence of <a href="https://physicsworld.com/a/cosmological-coupling-is-making-black-holes-bigger-study-suggests/">“cosmological coupling”</a>, which would mean that the growth of black holes over time is linked to the expansion of the universe itself.</p>
<p>The idea that black holes might contain something called <a href="https://en.wikipedia.org/wiki/Vacuum_energy">vacuum energy</a> (a manifestation of dark energy) is not particularly new and in fact was discussed theoretically as far back as the 1960s. But this latest work assumes this energy (and therefore the mass of the black holes) would increase with time as the universe expands as a result of cosmological coupling.</p>
<p>The team calculated how much of the dark energy in the universe could be attributed to this process. They found that black holes could potentially explain the total amount of dark energy we measure in the universe today. The result could solve one of the most fundamental problems in modern cosmology.</p>
<h2>Rapid expansion</h2>
<p><a href="https://hubblesite.org/contents/articles/the-big-bang">Our universe began in a Big Bang</a> around 13.7 billion years ago. The energy from this explosion of space and time caused the universe to expand rapidly, with all the galaxies flying away from each other. However, we expect that this expansion would gradually slow down because of the effect of gravity on all the stuff in the cosmos.</p>
<p>This is the version of the universe we thought we lived in until the late 1990s, when the Hubble space telescope discovered something strange. Observations of distant exploding stars showed that, in the past, the universe <a href="https://en.wikipedia.org/wiki/Accelerating_expansion_of_the_universe">was actually expanding more slowly than it is today</a>. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/gjwxnoPoEHQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The new discovery is explained by Chris Pearson of RAL Space and The Open University.</span></figcaption>
</figure>
<p>So the expansion of the universe has not been slowing due to gravity, as everyone thought, but instead has been accelerating. This was highly unexpected and astronomers struggled to explain it.</p>
<p>To account for this, it was proposed that a “dark energy” was responsible for pushing things apart more strongly than gravity pulled things together. The concept of dark energy was very similar to a mathematical construct Einstein had proposed but later discarded – a <a href="https://en.wikipedia.org/wiki/Cosmological_constant">“cosmological constant”</a> that opposed gravity and kept the universe from collapsing.</p>
<h2>Stellar explosions</h2>
<p>But what is dark energy? The solution, it seems, might lie with another cosmic mystery: black holes. Black holes are commonly born when <a href="https://public.nrao.edu/ask/when-does-a-neutron-star-or-black-hole-form-after-a-supernova/">massive stars explode and die at the ends of their lives</a>. The gravity and pressure in these violent explosions compresses vast amounts of material into a small space. For instance, a star about the same mass as our sun would be squashed into a space of just a few tens of kilometres. </p>
<p>A black hole’s gravitational pull is so strong that not even light can escape it – everything gets sucked in. At the centre of the black hole is a place called a <a href="https://bigthink.com/starts-with-a-bang/singularity-black-hole/">singularity</a>, where matter is crushed into a point of infinite density. The problem is that singularities are a mathematical construct that should not exist.</p>
<figure class="align-center ">
<img alt="The Andromeda galaxy" src="https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.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">Dark energy explains why the expansion of the universe is speeding up.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/galex/pia15416.html">NASA/JPL-Caltech</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The black holes nestled at the centres of galaxies are much heftier than those born when stars die violently. These galactic “supermassive” black holes can weigh millions to billions of times the mass of our Sun.</p>
<p>All black holes increase in size by accumulating matter, by swallowing stars that get too close, or by merging with other black holes. So we expect them to get bigger as the universe gets older.</p>
<p>In the latest paper, the team looked at supermassive black holes in the centres of galaxies and found that these black holes gain mass over billions of years. </p>
<h2>Radical rethink</h2>
<p>The team compared observations of <a href="https://en.wikipedia.org/wiki/Elliptical_galaxy">elliptical galaxies</a>, which lack star formation, in the past and in the present day. These dead galaxies have used up all their fuel so any increase in their black hole mass over this time cannot be ascribed to the normal processes by which black holes grow by accumulating matter.</p>
<p>Instead, the team proposed that these black holes actually contain vacuum energy and that they are “coupled” to the expansion of the universe, so that they increase in mass as the universe expands. </p>
<figure class="align-center ">
<img alt="Visualisation of a black hole" src="https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&rect=17%2C34%2C3782%2C2098&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?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">A visualisation of a black hole, which could play a role in dark energy.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/goddard/2019/nasa-visualization-shows-a-black-hole-s-warped-world">NASA’s Goddard Space Flight Center/Jeremy Schnittman</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>This model neatly provides a possible origin for the dark energy in the universe. It also circumvents the mathematical problems that affect some studies of black holes, because it avoids the need for a singularity at the centre.</p>
<p>The team also calculated how much of the dark energy in the universe could be attributed to this process of coupling. They concluded that it would be possible for black holes to provide the necessary amount of vacuum energy to account for all the dark energy that we measure in the universe today. </p>
<p>This would not only explain the origin of dark energy in the universe but would also make us radically rethink our understanding of black holes and their role in the cosmos.</p>
<p>Much more work needs to be done to test and confirm this idea, both from observations of the sky and from theory. But we may at last be seeing a new way to solve the problem of dark energy.</p><img src="https://counter.theconversation.com/content/199831/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Pearson receives funding from STFC and is head of astronomy at STFC RAL Space and a visiting fellow at the Open University </span></em></p><p class="fine-print"><em><span>Dave Clements receives funding from STFC and the UKSA and works at Imperial College London.</span></em></p>Astronomers have found that mysterious dark energy may originate in black holes.Chris Pearson, Astronomy Group Lead, Space Operations Division at RAL Space, and Visiting Fellow, The Open UniversityDave Clements, Reader in Astrophysics, Imperial College LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1876312022-07-31T20:05:55Z2022-07-31T20:05:55ZWe found some strange radio sources in a distant galaxy cluster. They’re making us rethink what we thought we knew.<figure><img src="https://images.theconversation.com/files/475823/original/file-20220725-24-3t22af.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C9315%2C9315&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The colliding cluster Abell 3266 as seen across the electromagnetic spectrum, using data from ASKAP and the ATCA (red/orange/yellow colours), XMM-Newton (blue) and the Dark Energy Survey (background map).</span> <span class="attribution"><span class="source">Christopher Riseley (Università di Bologna)</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The universe is littered with galaxy clusters – huge structures piled up at the intersections of the <a href="https://theconversation.com/a-thread-of-the-cosmic-web-astronomers-spot-a-50-million-light-year-galactic-filament-151569">cosmic web</a>. A single cluster can span millions of light-years across and be made up of hundreds, or even thousands, of galaxies.</p>
<p>However, these galaxies represent only a few percent of a cluster’s total mass. About 80% of it is <a href="https://theconversation.com/au/topics/dark-matter-95">dark matter</a>, and the rest is a hot plasma “soup”: gas heated to above 10,000,000°C and interwoven with weak magnetic fields.</p>
<p>We and our international team of colleagues have identified a series of rarely observed radio objects – a radio relic, a radio halo and fossil radio emission – within a particularly dynamic galaxy cluster called Abell 3266. They defy existing theories about both the origins of such objects and their characteristics.</p>
<h2>Relics, haloes and fossils</h2>
<p>Galaxy clusters allow us to study a broad range of rich processes – including magnetism and plasma physics – in environments we can’t recreate in our labs. </p>
<p>When clusters collide with each other, huge amounts of energy are put into the particles of the hot plasma, generating radio emission. And this emission comes in a variety of shapes and sizes. </p>
<p>“Radio relics” are one example. They are arc-shaped and sit towards a cluster’s outskirts, powered by shockwaves travelling through the plasma, which cause a jump in density or pressure, and energise the particles. An example of a shockwave on Earth is the sonic boom that happens when an aircraft breaks the sound barrier.</p>
<p>“Radio haloes” are irregular sources that lie towards the cluster’s centre. They’re powered by turbulence in the hot plasma, which gives energy to the particles. We know both haloes and relics are generated by collisions between galaxy clusters – yet many of their gritty details remain elusive. </p>
<p>Then there are “fossil” radio sources. These are the radio leftovers from the death of a supermassive black hole at the centre of a radio galaxy. </p>
<p>When they’re in action, black holes shoot huge jets <a href="https://theconversation.com/a-new-image-shows-jets-of-plasma-shooting-out-of-a-supermassive-black-hole-164709">of plasma</a> far out beyond the galaxy itself. As they run out of fuel and shut off, the jets begin to dissipate. The remnants are what we detect as radio fossils.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-radio-astronomy-7420">Explainer: radio astronomy</a>
</strong>
</em>
</p>
<hr>
<h2>Abell 3266</h2>
<p>Our <a href="https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stac1771">new paper</a>, published in the Monthly Notices of the Royal Astronomical Society, presents a highly detailed study of a galaxy cluster called Abell 3266.</p>
<p>This is a particularly dynamic and messy colliding system around 800 million light-years away. It has all the hallmarks of a system that <em>should</em> be host to relics and haloes – yet none had been detected until recently. </p>
<p>Following up on work conducted using the <a href="https://www.mwatelescope.org">Murchison Widefield Array</a> earlier <a href="https://doi.org/10.1093/mnras/stac335">this year</a>, we used new data from the <a href="https://theconversation.com/au/topics/askap-33989">ASKAP radio telescope</a> and the <a href="https://www.csiro.au/en/about/facilities-collections/ATNF/Australia-Telescope-Compact-Array">Australia Telescope Compact Array</a> (ATCA) to see Abell 3266 in more detail.</p>
<p>Our data paint a complex picture. You can see this in the lead image: yellow colours show features where energy input is active. The blue haze represents the hot plasma, captured at X-ray wavelengths.</p>
<p>Redder colours show features that are only visible at lower frequencies. This means these objects are older and have less energy. Either they have lost a lot of energy over time, or they never had much to begin with.</p>
<p>The radio relic is visible in red near the bottom of the image (see below for a zoom). And our data here reveal particular features that have never been seen before in a relic.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/475884/original/file-20220725-23-tpk3sc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/475884/original/file-20220725-23-tpk3sc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=321&fit=crop&dpr=1 600w, https://images.theconversation.com/files/475884/original/file-20220725-23-tpk3sc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=321&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/475884/original/file-20220725-23-tpk3sc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=321&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/475884/original/file-20220725-23-tpk3sc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=403&fit=crop&dpr=1 754w, https://images.theconversation.com/files/475884/original/file-20220725-23-tpk3sc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=403&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/475884/original/file-20220725-23-tpk3sc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=403&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The ‘wrong-way’ relic in Abell 3266 is shown here with yellow/orange/red colours representing the radio brightness.</span>
<span class="attribution"><span class="source">Christopher Riseley, using data from ASKAP, ATCA, XMM-Newton and the Dark Energy Survey)</span></span>
</figcaption>
</figure>
<p>Its concave shape is also unusual, earning it the catchy moniker of a “wrong-way” relic. Overall, our data break our understanding of how relics are generated, and we’re still working to decipher the complex physics behind these radio objects.</p>
<h2>Ancient remnants of a supermassive black hole</h2>
<p>The radio fossil, seen towards the upper right of the lead image (and also below), is very faint and red, indicating it is ancient. We believe this radio emission originally came from the galaxy at the lower left, with a central black hole that has long been switched off.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/476662/original/file-20220729-14-jfj12d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/476662/original/file-20220729-14-jfj12d.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=575&fit=crop&dpr=1 600w, https://images.theconversation.com/files/476662/original/file-20220729-14-jfj12d.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=575&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/476662/original/file-20220729-14-jfj12d.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=575&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/476662/original/file-20220729-14-jfj12d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=722&fit=crop&dpr=1 754w, https://images.theconversation.com/files/476662/original/file-20220729-14-jfj12d.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=722&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/476662/original/file-20220729-14-jfj12d.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=722&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The radio fossil in Abell 3266 is shown here with red colours and contours depicting the radio brightness measured by ASKAP, and blue colours showing the hot plasma. The cyan arrow points to the galaxy we think once powered the fossil.</span>
<span class="attribution"><span class="source">Christopher Riseley, using data from ASKAP, XMM-Newton and the Dark Energy Survey</span></span>
</figcaption>
</figure>
<p>Our best physical models simply can’t fit the data. This reveals gaps in our understanding of how these sources evolve – gaps that we’re working to fill.</p>
<p>Finally, using a clever algorithm, we de-focused the lead image to look for very faint emission that’s invisible at high resolution, unearthing the first detection of a radio halo in Abell 3266 (see below).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/476659/original/file-20220729-5473-l4tehb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/476659/original/file-20220729-5473-l4tehb.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=576&fit=crop&dpr=1 600w, https://images.theconversation.com/files/476659/original/file-20220729-5473-l4tehb.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=576&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/476659/original/file-20220729-5473-l4tehb.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=576&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/476659/original/file-20220729-5473-l4tehb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=724&fit=crop&dpr=1 754w, https://images.theconversation.com/files/476659/original/file-20220729-5473-l4tehb.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=724&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/476659/original/file-20220729-5473-l4tehb.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=724&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The radio halo in Abell 3266 is shown here with red colours and contours depicting the radio brightness measured by ASKAP, and blue colours showing the hot plasma. The dashed cyan curve marks the outer limits of the radio halo.</span>
<span class="attribution"><span class="source">Christopher Riseley, using data from ASKAP, XMM-Newton and the Dark Energy Survey</span></span>
</figcaption>
</figure>
<h2>Towards the future</h2>
<p>This is the beginning of the road towards understanding Abell 3266. We have uncovered a wealth of new and detailed information, but our study has raised yet more questions.</p>
<p>The telescopes we used are laying the foundations for revolutionary science from the <a href="https://www.skao.int">Square Kilometre Array</a> project. Studies like ours allow astronomers to figure out what we don’t know – but you can be sure we’re going to find out.</p>
<hr>
<p><em>We acknowledge the Gomeroi people as the traditional owners of the site where ATCA is located, and the Wajarri Yamatji people as the traditional owners of the Murchison Radioastronomy Observatory site, where ASKAP and the Murchison Widefield Array are located.</em></p><img src="https://counter.theconversation.com/content/187631/count.gif" alt="The Conversation" width="1" height="1" />
<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><p class="fine-print"><em><span>Tessa Vernstrom works for the International Centre for Radio Astronomy Research (ICRAR) at the University of Western Australia. She is affiliated with CSIRO Space & Astronomy. </span></em></p>One of the objects is a ‘fossil’ radio source – a leftover from the death of a supermassive black hole that once shot out huge jets of plasma.Christopher Riseley, Research Fellow, Università di BolognaTessa Vernstrom, Senior research fellow, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1830082022-05-12T22:33:48Z2022-05-12T22:33:48ZSay hello to Sagittarius A*, the black hole at the center of the Milky Way galaxy<figure><img src="https://images.theconversation.com/files/462875/original/file-20220512-14-m27nc1.jpeg?ixlib=rb-1.1.0&rect=107%2C83%2C7257%2C4189&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This image shows Sagittarius A*, the black hole at the center of the Milky Way galaxy. </span> <span class="attribution"><a class="source" href="https://eventhorizontelescope.org/blog/astronomers-reveal-first-image-black-hole-heart-our-galaxy">EHT Collaboration</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p><em>On May 12, 2022, astronomers on the Event Horizon Telescope team <a href="https://eventhorizontelescope.org/blog/astronomers-reveal-first-image-black-hole-heart-our-galaxy">released an image of a black hole called Sagittarius A*</a> that lies at the center of the Milky Way galaxy. Chris Impey, an astronomer at the University of Arizona, explains how the team got this image and why it is such a big deal.</em></p>
<h2>1. What is Sagittarius A*?</h2>
<p>Sagittarius A* sits at the the center of our Milky Way galaxy, in the direction of the Sagittarius constellation. For decades, astronomers have been <a href="https://armaghplanet.com/karl-jansky-the-father-of-radio-astronomy.html">measuring blasts of radio waves</a> from an extremely compact source there.</p>
<p>In the 1980s, two teams of astronomers started tracking the motions of stars near this mysterious source of radio waves. They saw stars whirling around a dark object at speeds up to a third of the speed of light. Their motions suggested that at the center of the Milky Way was a black hole <a href="https://iopscience.iop.org/article/10.1086/592738">4 million times the mass of the Sun</a>. Reinhard Genzel and Andrea Ghez later shared the <a href="https://www.nobelprize.org/prizes/physics/2020/summary/">Nobel Prize in Physics</a> for this discovery.</p>
<p>The size of a black hole is defined by its <a href="https://www.space.com/black-holes-event-horizon-explained.html">event horizon</a> – a distance from the center of the black hole within which nothing can escape. Scientists had previously been able to calculate that Sagittarius A* is 16 million miles (26 million kilometers) in diameter.</p>
<p>The Milky Way’s black hole is huge compared to the <a href="https://astronomy.com/news/2021/09/what-are-stellar-mass-black-holes">black holes left behind when massive stars die</a>. But astronomers think there are supermassive black holes at the center of nearly all galaxies. Compared to most of these, Sagittarius A* is meager and unremarkable.</p>
<h2>2. What does the new image show?</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/462875/original/file-20220512-14-m27nc1.jpeg?ixlib=rb-1.1.0&rect=107%2C83%2C7257%2C4189&q=45&auto=format&w=1000&fit=clip"><img alt="An image showing a donut-shaped cloud of reddish-orange gas." src="https://images.theconversation.com/files/462875/original/file-20220512-14-m27nc1.jpeg?ixlib=rb-1.1.0&rect=107%2C83%2C7257%2C4189&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/462875/original/file-20220512-14-m27nc1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/462875/original/file-20220512-14-m27nc1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/462875/original/file-20220512-14-m27nc1.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/462875/original/file-20220512-14-m27nc1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/462875/original/file-20220512-14-m27nc1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/462875/original/file-20220512-14-m27nc1.jpeg?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">It’s impossible to take a direct image of a black hole because no light can escape its gravity. But it is possible to measure the radio waves emitted by the gas that surrounds a black hole.</span>
<span class="attribution"><a class="source" href="https://eventhorizontelescope.org/blog/astronomers-reveal-first-image-black-hole-heart-our-galaxy">EHT Collaboration</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Black holes themselves are completely dark, since nothing, not even light, can escape their gravity. But black holes are surrounded by clouds of gas, and astronomers can measure this gas to infer images of the black holes within. The central dark region in the image is a shadow cast by the black hole onto the gas. The bright ring is the gas itself glowing. The bright spots in the ring show areas of hotter gas that may one day fall into the black hole. </p>
<p>Some of the gas visible in the image is actually behind Sagittarius A*. Light from that gas is being bent by the powerful gravity of the black hole toward Earth. This effect, called <a href="https://earthsky.org/space/what-is-gravitational-lensing-einstein-ring/">gravitational lensing</a>, is a core prediction of <a href="https://vis.sciencemag.org/generalrelativity/">general relativity</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/462891/original/file-20220512-10218-78uxmx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A red mass of gas and stars at the center of the Milky Way." src="https://images.theconversation.com/files/462891/original/file-20220512-10218-78uxmx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/462891/original/file-20220512-10218-78uxmx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=433&fit=crop&dpr=1 600w, https://images.theconversation.com/files/462891/original/file-20220512-10218-78uxmx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=433&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/462891/original/file-20220512-10218-78uxmx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=433&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/462891/original/file-20220512-10218-78uxmx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=544&fit=crop&dpr=1 754w, https://images.theconversation.com/files/462891/original/file-20220512-10218-78uxmx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=544&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/462891/original/file-20220512-10218-78uxmx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=544&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Galactic cores, like the center of the Milky Way seen in this photo, are full of gas and debris, making it very hard to get any direct images of the stars or black holes there.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/nasamarshall/48903707543/in/photolist-2hvshtr-2ndE1xx-2n1dcaM-28yz69J-2miK8fB-2mGGtrb-2maPoRT-2mGLCXm-2mw7HYc-2mPV9tG-Q92K4K-2jKs7Gn-2hn6G22-7eLryh-2jC1xCg-2mnUcrn-2mLh5cj-JxJ7be-2mtMvaE-2kE3t2z-2m74ZcB-2kyX69B-2m251Hc-CMxXkS-K4F2jc-GN1Bku-JgNddt-23QYYhw-2hNmN6G-RwLqLM-2huWAyT-QJQ4o6-B8gBjZ-2gUfsHN-2jbsvYR-QhWA5d-2i9UMm7-2gbPbvV-2aPQ2ez-2fa6n57-2gKPP7W-2ioJdhF-2mQBHJB-2f33vn7-2hJMvxS-YafGbq-2kmqFa7-2m3dZde-22hY3QU-23XHKpW/">NASA/JPL-Caltech</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>3. What went into producing this image?</h2>
<p>Supermassive black holes are extremely hard to measure. They are far away and shrouded by the gas and dust that clogs the center of galaxies. They are also relatively small compared to the vastness of space. From where Sagittarius A* sits, 26,000 light years away at the center of the Milky Way, only 1 in 10 billion photons of visible light can reach Earth – most are absorbed by gas in the way. Radio waves pass through gas much more easily than visible light, so astronomers measured the radio emissions from the gas surrounding the black hole. The orange colors in the image are representations of those radio waves.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/462890/original/file-20220512-16-dmak1o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Lines connecting point on the globe connecting eight different areas across the Earth." src="https://images.theconversation.com/files/462890/original/file-20220512-16-dmak1o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/462890/original/file-20220512-16-dmak1o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/462890/original/file-20220512-16-dmak1o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/462890/original/file-20220512-16-dmak1o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/462890/original/file-20220512-16-dmak1o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/462890/original/file-20220512-16-dmak1o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/462890/original/file-20220512-16-dmak1o.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 researchers used eight telescopes from around the globe – located at the points where the white lines intersect – to act as a single, massive telescope.</span>
<span class="attribution"><a class="source" href="https://drive.google.com/drive/folders/1SVCkvW9yoUEELzOQISQlvo9lgQUeETUq">ESO/L. Calçada</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The team used <a href="https://eventhorizontelescope.org/array">eight radio telescopes spread across the globe</a> to collect data on the black hole over the course of five nights in 2017. Every night generated so much data that the team couldn’t send it through the internet – they had to ship physical hard drives to where they processed the data. </p>
<p>Because black holes are so hard to see, there is a lot of uncertainty in the data the telescopes collect. To turn it all into an accurate image, team used <a href="https://vis.sciencemag.org/generalrelativity/">supercomputers to produce millions of different images</a>, each one a mathematically viable version of the black hole based off the data collected and the laws of physics. They then blended all of these images together to produce the final, beautiful, accurate image. The processing time was equivalent to running 2,000 laptops at full speed for a year.</p>
<h2>4. Why is the new image such a big deal?</h2>
<p>In 2019, the Event Horizon Telescope team released the <a href="https://www.space.com/first-black-hole-photo-by-event-horizon-telescope.html">first image of a black hole</a> – this one at the center of the galaxy M87. The black hole at the center of this galaxy, named M87*, is a behemoth 2,000 times larger than Sagittarius A* and 7 billion times the mass of the Sun. But because Sagittarius A* is 2,000 times closer to Earth than M87*, the Event Horizon Telescope was able to observe both black holes at a similar resolution – giving astronomers a chance to learn about the universe by comparing the two.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/462889/original/file-20220512-12-m1sdnk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two side by side images of red, donut-shaped clouds of gas surrounding black holes." src="https://images.theconversation.com/files/462889/original/file-20220512-12-m1sdnk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/462889/original/file-20220512-12-m1sdnk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=351&fit=crop&dpr=1 600w, https://images.theconversation.com/files/462889/original/file-20220512-12-m1sdnk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=351&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/462889/original/file-20220512-12-m1sdnk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=351&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/462889/original/file-20220512-12-m1sdnk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=441&fit=crop&dpr=1 754w, https://images.theconversation.com/files/462889/original/file-20220512-12-m1sdnk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=441&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/462889/original/file-20220512-12-m1sdnk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=441&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">M87*, on the left, is 2,000 times bigger than Sagittarius A*, on the right. The thin white circles indicate sizes of orbits of planets in the solar system.</span>
<span class="attribution"><a class="source" href="https://drive.google.com/drive/folders/1JXzExotCHcUUykXbYssBUYLkLW-BIGxR">EHT collaboration (acknowledgment: Lia Medeiros, xkcd)</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The similarity of the two images is striking because small stars and small galaxies look and behave very differently than large stars or galaxies. Black holes are the only objects in existence that only answer to one law of nature – gravity. And <a href="https://news.arizona.edu/story/black-hole-scientist-wherever-we-look-we-should-see-donuts">gravity does not care about scale</a>.</p>
<p>For the last few decades, astronomers have thought that there are massive black holes at the center of <a href="https://hubblesite.org/contents/news-releases/1997/news-1997-01.html">almost every galaxy</a>. While M87* is an unusually huge black hole, Sagittarius A* is likely pretty similar to many of the hundreds of billions of black holes at the center of other galaxies in the universe. </p>
<h2>5. What scientific questions can this answer?</h2>
<p>There is a lot more science to be done from the data the team collected. </p>
<p>One interesting avenue of inquiry stems from the fact that the gas surrounding Sagittarius A* is moving at close to the speed of light. Sagittarius A* is relatively small, and matter <a href="https://www.france24.com/en/science/20220512-scientists-unveil-image-of-black-hole-at-milky-way-s-centre">trickles into it very slowly</a> – if it were the size of a human, it would consume the mass of a single grain of rice every million years. But by taking many images, it would be possible to watch the flow of matter around and into the black hole in real time. This would allow astrophysicists to study how black holes consume matter and grow.</p>
<p>A picture is worth a thousand words, and this new image has already generated <a href="https://iopscience.iop.org/journal/2041-8205/page/Focus_on_First_Sgr_A_Results">10 scientific papers</a>. I expect there will be many more to come.</p><img src="https://counter.theconversation.com/content/183008/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation. </span></em></p>Sagittarius A* is a massive black hole at the center of the Milky Way. Now that astronomers have imaged it, they can begin to learn more about black holes within other galaxies across the universe.Chris Impey, University Distinguished Professor of Astronomy, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1830102022-05-12T19:14:22Z2022-05-12T19:14:22ZHow we captured first image of the supermassive black hole at centre of the Milky Way<figure><img src="https://images.theconversation.com/files/462857/original/file-20220512-18-5tg6yz.jpeg?ixlib=rb-1.1.0&rect=6%2C225%2C3746%2C3764&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Revealed: Sagittarius A*.</span> <span class="attribution"><span class="source">EHT Collaboration/ESO</span></span></figcaption></figure><p>Black holes are among the most profound predictions of Einstein’s theory of general relativity. Originally studied as a mere mathematical consequence of the theory rather than as physically relevant objects, they soon became thought of as generic and sometimes inevitable outcomes of the gravitational collapse that initially forms a galaxy.</p>
<p>In fact, most physicists have suspected that our own galaxy revolves around a supermassive black hole at its centre. There are other ideas too – such as “dark matter” (an invisible substance thought to make up most of the matter in the universe). But now an international team of astronomers, including a team that I led from the University of Central Lancashire, <a href="https://iopscience.iop.org/journal/2041-8205/page/Focus_on_First_Sgr_A_Results">has unveiled the first image</a> of the object lurking at the centre of the Milky Way – and it is a supermassive black hole.</p>
<p>This means there is now overwhelming evidence for the black hole, dubbed Sagittarius A*. While it might seem a little scary to be so close to such a beast, it is in fact some 26,000 light-years away, which is reassuringly far. In fact, because the black hole is so far away from Earth, it appears to us to have about the same size in the sky as a donut would have on the Moon. Sagittarius A* also seems rather inactive – it is not devouring a lot of matter from its surroundings.</p>
<p>Our team was part of the global Event Horizon Telescope (EHT) Collaboration, which has used observations from a worldwide network of eight radio telescopes on our planet – collectively forming a single, Earth-sized virtual telescope – to take the stunning image. The breakthrough follows the collaboration’s 2019 release of <a href="https://theconversation.com/first-black-hole-photo-confirms-einsteins-theory-of-relativity-115167">the first ever image of a black hole</a>, called M87*, at the centre of the more distant <a href="https://www.nasa.gov/feature/goddard/2017/messier-87">Messier 87 galaxy</a>.</p>
<h2>Looking into darkness</h2>
<p>The team observed Sagittarius A* on multiple nights, collecting data for many hours in a row, similar to using a long exposure time on a camera. Although we cannot see the black hole itself, because it is completely dark, glowing gas around it reveals a tell-tale signature: a dark central region (called a “shadow”) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun. The discovery also yields valuable clues about the workings of black holes, which are thought to reside at the centre of most galaxies.</p>
<figure class="align-center ">
<img alt="Image of ALMA – one of the Event Horizon telescopes." src="https://images.theconversation.com/files/462859/original/file-20220512-5542-4lmhll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/462859/original/file-20220512-5542-4lmhll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/462859/original/file-20220512-5542-4lmhll.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/462859/original/file-20220512-5542-4lmhll.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/462859/original/file-20220512-5542-4lmhll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/462859/original/file-20220512-5542-4lmhll.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/462859/original/file-20220512-5542-4lmhll.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">ALMA – one of the Event Horizon telescopes.</span>
<span class="attribution"><span class="source">wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The surprising thing about this image is that it looks so similar to the image of M87* we published three years ago – this certainly came as a surprise. The reason for the similarity is that while the M87* black hole is about 1,000 times bigger, the Sagittarius black hole is about 100 times closer. Both of them obey Einstein’s theory of general relativity, showing Einstein was right for a factor of 1,000 in size scale. To a physicist this is important. Relativity has been around for a century and it is still proving to be accurate. I think even Einstein himself might have been surprised by that!</p>
<p>The publication of the picture of the Sagittarius A* black hole is a tremendously exciting achievement by the collaboration. When I first saw the image, I thought: this tells us a lot. I couldn’t wait to start writing about it and interpreting the image. We had a lot of meetings to come to a consensus of what it tells us. To begin with we were meeting face to face in different parts of the world. Then COVID struck and suddenly nobody could go anywhere. So online meetings became the norm, as in every other aspect of life. This definitely slowed us down.</p>
<p>My role was to help write two of the <a href="https://iopscience.iop.org/journal/2041-8205/page/Focus_on_First_Sgr_A_Results">six papers</a> that have been released in the Astrophysical Journal Letters: the first one, introducing the observation; and the third one, in which we discuss how we made a picture out of the observations, and how reliable that image is. </p>
<p>In addition, I was a “contributing author” for all six papers. This is an administrative role, in which I handled all correspondence between our team of over 300 astronomers and the academic journal that published our findings. This had its challenges, as I had to deal with every typo and every mistake in the typesetting.</p>
<p>I also had to channel comments from my colleagues. Since the majority of the collaborators are based in either the US or East Asia, it meant that they were working during the night in UK time. Hence, each morning I would come to work to find about 100 overnight emails from colleagues – a daunting start to any day.</p>
<p>Anyway, we got there in the end – and the dazzling result was worth all of the work.</p><img src="https://counter.theconversation.com/content/183010/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Derek Ward-Thompson 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>We finally know that Sagittarius A* really exists.Derek Ward-Thompson, Professor of Astrophysics, University of Central LancashireLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1699382021-12-14T00:04:18Z2021-12-14T00:04:18ZSome black holes are anything but black – and we’ve found more than 75,000 of the brightest ones<figure><img src="https://images.theconversation.com/files/427670/original/file-20211021-15-77a6an.jpeg?ixlib=rb-1.1.0&rect=3%2C51%2C1274%2C1230&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="http://www.eso.org/public/images/eso0903a/">ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>When the most massive stars die, they collapse to form some of the densest objects known in the Universe: black holes. They are the “darkest” objects in the cosmos, as not even light can escape their incredibly strong gravity. </p>
<p>Because of this, it’s impossible to directly image black holes, making them mysterious and quite perplexing. But our <a href="https://academic.oup.com/mnras/article-abstract/509/4/4940/6458741?redirectedFrom=fulltext">new research</a> has road-tested a way to spot some of the most voracious black holes of all, making it easier to find them buried deep in the hearts of distant galaxies.</p>
<p>Despite the name, not all black holes are black. While black holes come in many different sizes, the biggest ones are at the centres of galaxies, and are still growing in size. </p>
<p>These “supermassive” black holes can have the mass of up to a <a href="https://theconversation.com/overmassive-black-hole-holds-the-mass-of-17-billion-suns-11066">billion Suns</a>. The black hole at the centre of our own Milky Way galaxy – called Sagittarius A*, whose discovery received the <a href="https://www.nobelprize.org/prizes/physics/2020/press-release/">2020 Nobel Prize in Physics</a> – is fairly calm. But that isn’t the case for all supermassive black holes. </p>
<p>If material such as gas, dust or stars gets too close to a black hole, it gets sucked in by the enormous gravitational force. As it falls towards the black hole, it heats up and becomes incredibly bright. </p>
<p>The light produced by these “bright black holes” can span the entire electromagnetic spectrum, from X-rays to radio waves. Another name for the bright black holes at the centre of galaxies is “active galactic nuclei”, or AGN. They can shine trillions of times brighter than the Sun, and can sometimes even outshine all the stars in its galaxy.</p>
<figure class="align-center ">
<img alt="Image of black hole" src="https://images.theconversation.com/files/427657/original/file-20211020-20-6ejhs1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/427657/original/file-20211020-20-6ejhs1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/427657/original/file-20211020-20-6ejhs1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/427657/original/file-20211020-20-6ejhs1.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/427657/original/file-20211020-20-6ejhs1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/427657/original/file-20211020-20-6ejhs1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/427657/original/file-20211020-20-6ejhs1.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Matter swirling into the supermassive black hole at the centre of M87.</span>
<span class="attribution"><span class="source">Event Horizon Telescope</span></span>
</figcaption>
</figure>
<h2>The brightest black holes</h2>
<p>Some <a href="https://theconversation.com/radio-galaxies-the-mysterious-secretive-beasts-of-the-universe-64381">AGN violently spew out matter via a jet</a>, which travels millions of kilometres through space and can be seen by radio telescopes. Others produce “winds” at the centre of the galaxy, capable of pushing any gas (the fuel needed for stars to form) out of the galaxy. </p>
<figure class="align-center ">
<img alt="Violent jets spewing from Hercules A" src="https://images.theconversation.com/files/427660/original/file-20211021-27-yh2j20.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/427660/original/file-20211021-27-yh2j20.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=426&fit=crop&dpr=1 600w, https://images.theconversation.com/files/427660/original/file-20211021-27-yh2j20.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=426&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/427660/original/file-20211021-27-yh2j20.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=426&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/427660/original/file-20211021-27-yh2j20.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=536&fit=crop&dpr=1 754w, https://images.theconversation.com/files/427660/original/file-20211021-27-yh2j20.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=536&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/427660/original/file-20211021-27-yh2j20.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=536&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Violent jets spewing from Hercules A.</span>
<span class="attribution"><span class="source">NASA/ESA/NRAO</span></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/like-a-spinning-top-wobbling-jets-from-a-black-hole-thats-feeding-on-a-companion-star-116067">Like a spinning top: wobbling jets from a black hole that's 'feeding' on a companion star</a>
</strong>
</em>
</p>
<hr>
<p>With such destructive forces in the middle of a galaxy, astronomers are certain this must have a big impact on the galaxy itself. We know most galaxies are slowly <a href="https://theconversation.com/dont-panic-but-the-universe-is-slowly-dying-45779">turning off their star formation processes</a>, and AGN might be one of the culprits.</p>
<p>AGN can therefore not only help us to better understand elusive black holes, but studying them also teaches us about galaxies themselves. </p>
<h2>Finding bright black holes</h2>
<p>Depending on how much a black hole is “eating”, what galaxy it’s in, and the angle from which we can see it, AGN can look very different to one another. Even when looking at the same galaxy, one astronomer with an X-ray telescope may see it glow and discover an AGN, whereas another astronomer using a radio telescope might see nothing, if the AGN doesn’t happen to produce jets that are visible in the radio spectrum. </p>
<p>Because of this, it was thought they were all different objects, but by looking at the same objects with different telescopes astronomers discovered they had many similarities, and realised the benefits of using more of the electromagnetic spectrum to find them. </p>
<p>The relative brightness of a galaxy across different parts of the electromagnetic spectrum is called its “spectral energy distribution”. This can be used to measure how many stars are in a galaxy, how old they are, what they’re made of, and how much dust is blocking the light. </p>
<figure class="align-center ">
<img alt="Image of galaxy at different wavelengths" src="https://images.theconversation.com/files/427658/original/file-20211021-66011-xlzg8t.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/427658/original/file-20211021-66011-xlzg8t.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=443&fit=crop&dpr=1 600w, https://images.theconversation.com/files/427658/original/file-20211021-66011-xlzg8t.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=443&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/427658/original/file-20211021-66011-xlzg8t.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=443&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/427658/original/file-20211021-66011-xlzg8t.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=556&fit=crop&dpr=1 754w, https://images.theconversation.com/files/427658/original/file-20211021-66011-xlzg8t.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=556&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/427658/original/file-20211021-66011-xlzg8t.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=556&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Composite picture showing how a typical galaxy appears at different wavelengths.</span>
<span class="attribution"><span class="source">ICRAR/GAMA and ESO</span></span>
</figcaption>
</figure>
<p>In our research, <a href="https://academic.oup.com/mnras/article-abstract/509/4/4940/6458741?redirectedFrom=fulltext">published today</a> in Monthly Notices of the Royal Astronomical Society, we show that this technique can also be used to spot AGN. This means we can now measure not just the properties and histories of the stars in the galaxy, but also the brightness of its central black hole. </p>
<p>It’s not a simple thing to do. The difference between starlight and the light from an AGN is incredibly subtle, so it’s possible to confuse young stars for a bright black hole, and vice versa. </p>
<p>Here in Australia, astronomers have been <a href="https://theconversation.com/explainer-seeing-the-universe-through-spectroscopic-eyes-37759">using Australian telescopes</a> to make 3D maps of galaxies in specific patches of the sky. These maps let us scour hundreds of thousands of galaxies, spanning 11 billion years of history, for possible AGN. </p>
<p>By applying our new method to 700,000 galaxies we identified and quantified more than 75,000 AGN to begin understanding how their number has evolved over time and how they have impacted their host galaxies. Astronomers think the number of AGN in the Universe is linked to the amount of star formation, which we know was almost ten times higher roughly 10 billion years ago. But until we can be certain we’ve identified all the AGN across cosmic time in our galaxy samples, we won’t know for sure.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-heaviest-stellar-black-hole-in-our-galaxy-is-even-more-massive-than-we-thought-155484">The heaviest stellar black hole in our galaxy is even more massive than we thought</a>
</strong>
</em>
</p>
<hr>
<p>Right now, the astronomical community is still passionately debating the nature of active black holes. While we haven’t yet answered the questions needed to soothe the debate, we’re now one step closer to reliably being able to spot these fascinating objects within galaxies. And that’s an important step towards shedding more light on the mystery of black holes.</p><img src="https://counter.theconversation.com/content/169938/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jessica Thorne is supported by the Australian Government Research Traning Program (RTP) Scholarship. </span></em></p><p class="fine-print"><em><span>Sabine Bellstedt receives funding from the Australian Research Council. </span></em></p>Despite the name, some black holes effectively “shine” as they suck up nearby material with such force that it begins to glow. New research reveals a new method for detecting these active black holes.Jessica Thorne, Astrophysics PhD Candidate, The University of Western AustraliaSabine Bellstedt, Research Associate in Astronomy, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1719072021-11-25T12:20:15Z2021-11-25T12:20:15ZCurious Kids: how are galaxies formed?<figure><img src="https://images.theconversation.com/files/433499/original/file-20211123-17-199wbff.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5991%2C3395&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">There's a lot we don't know about galaxies. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/planets-stars-galaxies-outer-space-showing-1608969370">Zakharchuk/Shutterstock</a></span></figcaption></figure><p><strong>How are galaxies formed? – Harsh, aged 14, Kolkata, India</strong></p>
<p>To answer the question of how galaxies were formed, we need to travel back in time to close to the birth of the universe, nearly <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question28.html">14 billion years</a> ago. The great thing about the universe is that we can do exactly that. Because light takes time to travel to us, when we look at a distant galaxy we are seeing it as it was in the past.</p>
<p>The furthest back we can look is 400,000 years after the <a href="https://astronomy.swin.edu.au/cosmos/e/epoch+of+recombination">birth of the universe</a>.
If we imagine the history of the universe as being the length of a person’s life, this would be like looking back to about 20 hours after they were born. What we see is a wall of glow. This is the <a href="https://www.space.com/33892-cosmic-microwave-background.html">cosmic microwave background light</a> left from the mighty Big Bang that created the universe.</p>
<h2>The creation of matter</h2>
<p>The Big Bang first created a stupendous amount of space, and three minutes later filled it with stuff – what we call <a href="https://www.nasa.gov/audience/forstudents/k-4/dictionary/Matter.html">matter</a>. But this matter was not evenly spread out. It was clumped together in strings and knots called the “<a href="https://svs.gsfc.nasa.gov/10118">cosmic web</a>”. We can see this in the wall of light – it does not have an even colour. There are clumps of colour reflecting where matter was lumped together. </p>
<hr>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
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<p><em><a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a> is a series by <a href="https://theconversation.com/uk">The Conversation</a> that gives children the chance to have their questions about the world answered by experts. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskids@theconversation.com">curiouskids@theconversation.com</a>. We won’t be able to answer every question, but we’ll do our very best.</em></p>
<hr>
<p>As the universe cooled, gravity started to draw matter towards those clumps. Where it piled up sufficiently, gravity really took off, pulling matter together, until the first stars were born that lit up the universe. Each clump of matter created myriad stars. </p>
<p>We don’t know whether each of these clumps became a galaxy, or whether clumps merged together to form bigger galaxies.</p>
<p>Another mystery is added by the <a href="https://science.nasa.gov/astrophysics/focus-areas/black-holes">supermassive black holes</a> that lurk at the centre of all big galaxies. Black holes are regions in space where gravity is so strong that even light cannot escape. One four million times as massive as the Sun resides in the heart of our own Milky Way. The bigger the galaxy, the bigger the black hole it surrounds. This tells us there must be a close connection between the development of galaxies and of these black holes.</p>
<figure class="align-center ">
<img alt="Black circle at centre of points of light" src="https://images.theconversation.com/files/433746/original/file-20211124-23-mpk3s2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/433746/original/file-20211124-23-mpk3s2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=594&fit=crop&dpr=1 600w, https://images.theconversation.com/files/433746/original/file-20211124-23-mpk3s2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=594&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/433746/original/file-20211124-23-mpk3s2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=594&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/433746/original/file-20211124-23-mpk3s2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=746&fit=crop&dpr=1 754w, https://images.theconversation.com/files/433746/original/file-20211124-23-mpk3s2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=746&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/433746/original/file-20211124-23-mpk3s2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=746&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A computer-simulated image of a supermassive black hole at the centre of a galaxy.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/details-behemoth-black-hole-found-in-an-unlikely-place_26209716511_o">NASA, ESA, and D. Coe, J. Anderson, and R. van der Marel (STScI)</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>However, we don’t really know how these black holes formed. We do know this must have happened very early on in the history of the universe. One idea is that the densest clumps of matter might have collapsed to become a black hole. Another is that the first stars to have lived and died left black holes, and these then merged together to become a huge single black hole.</p>
<p>It turns out that, if we think we understand gravity, there must be an awful lot more matter in the universe than we can see. Astronomers have given it a name: “<a href="https://www.nasa.gov/content/discoveries-highlights-shining-a-light-on-dark-matter">dark matter</a>”. The cosmic web is thought of as being largely made of dark matter. We think that galaxies are typically made up of more dark matter than ordinary matter, and that there’s even more in between galaxies. If this is right, dark matter must have had a huge effect on the formation of galaxies, but we don’t know exactly how.</p>
<h2>Still growing</h2>
<p>The creation of groups of stars from the matter produced by the Big Bang is not the end of the story. Take the Milky Way as a typical example. The oldest stars in the galaxy are spread out in a halo. These stars are made almost entirely of the first building blocks of the Universe – hydrogen and helium. </p>
<figure class="align-center ">
<img alt="Night sky with ribbon of cloud and light" src="https://images.theconversation.com/files/433747/original/file-20211124-13-1ltth0a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/433747/original/file-20211124-13-1ltth0a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=348&fit=crop&dpr=1 600w, https://images.theconversation.com/files/433747/original/file-20211124-13-1ltth0a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=348&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/433747/original/file-20211124-13-1ltth0a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=348&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/433747/original/file-20211124-13-1ltth0a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=437&fit=crop&dpr=1 754w, https://images.theconversation.com/files/433747/original/file-20211124-13-1ltth0a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=437&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/433747/original/file-20211124-13-1ltth0a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=437&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Milky Way as seen from Earth.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/summer-milky-way-rises-over-macdonald-121254331">John A Davis/Shutterstock</a></span>
</figcaption>
</figure>
<p>Closer to the centre of the galaxy, and in a flat disc around it, stars often contain a <a href="https://www.sciencelearn.org.nz/resources/1727-how-elements-are-formed">lot more other elements</a>, such as carbon and oxygen. These stars were formed out of the ashes of exploded stars that created those elements. As well as new stars, these elements went on to form planets – like our Earth.</p>
<p>The Milky Way is still growing, in two ways. There’s actually a lot of matter in between galaxies. When the temperature of this matter cools it can <a href="https://esahubble.org/images/opo9946a/">rain onto the Milky Way</a> and fuel the formation of new stars. Also, the pull of the Milky Way’s gravity means that it gobbles up entire <a href="https://www.esa.int/Science_Exploration/Space_Science/Gaia/Five_fascinating_Gaia_revelations_about_the_Milky_Way">small dwarf galaxies</a>.</p>
<p>Eventually, all these processes will fizzle out and the Milky Way will transform into a galaxy of old, red stars.</p>
<hr>
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<p class="fine-print"><em><span>Jacco van Loon 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>We have to look back to the Big Bang to find out.Jacco van Loon, Astronomer, Keele UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1647092021-07-20T02:49:51Z2021-07-20T02:49:51ZA new image shows jets of plasma shooting out of a supermassive black hole<figure><img src="https://images.theconversation.com/files/412048/original/file-20210720-19-ragc5m.jpg?ixlib=rb-1.1.0&rect=4%2C36%2C278%2C278&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Event Horizon Telescope project/Nature Astronomy</span></span></figcaption></figure><p>In 2019, when astronomers captured the first image of a <a href="https://iopscience.iop.org/article/10.3847/2041-8213/ab1141">black hole’s shadow</a> — a bright orange doughnut-shaped halo created by the black hole’s intense gravity bending light around it — it was rightly <a href="https://www.sciencemag.org/news/2019/04/black-hole">hailed as a breakthrough</a>. </p>
<p>Now, I have joined the <a href="https://eventhorizontelescope.org/">Event Horizon Telescope</a> team in following up on their earlier achievement, by creating a new image showing jets of plasma being ejected from the core of a different supermassive black hole, at the centre of the galaxy Centaurus A.</p>
<p>Centaurus A’s black hole is about 120 times less massive than that of M87, the galaxy where the black hole halo was spotted (and which also has its own set of plasma jets). So no black hole shadow was expected or seen in Centaurus A’s case.</p>
<p>But the results, <a href="https://www.nature.com/articles/s41550-021-01417-w">published in Nature Astronomy</a>, nevertheless provide another fascinating insight into the huge black holes that lurk at the centre of many galaxies.</p>
<p>Centaurus A is so-named because it is the brightest (hence “A”) object in the constellation Centaurus, in the southern skies. Centaurus A appears as one of the largest radio galaxies in our skies, because of its relative closeness, at 15 million light years from Earth.</p>
<p>In the visible light spectrum, this galaxy is characterised by a dark “dust lane” that blocks our view of its centre. But radio waves are unaffected by this material, so radioastronomers can study its centre in detail. </p>
<p>Centaurus A, like other “active” galaxies, has a supermassive black hole at its centre, which is fed by material falling in towards it. Much of that material ends up falling into, or orbiting around, the black hole. But some of it – through a process not yet understood – is shot out in a pair of diametrically opposed “jets”.</p>
<p>These plasma jets are one of the most mysterious and energetic features of galaxies. They travel at speeds close to the speed of light, and so the effects of Einstein’s theory of relativity become important. </p>
<p>One prediction is that the jet travelling towards us will appear brighter, while the opposing jet, travelling away from us, will appear fainter.</p>
<p>In fact, detailed studies of most active galaxies only reveal a one-sided jet, with the counter-jet too faint to observe.</p>
<p>Centaurus A is one of the few examples for which both the jet and counter-jet have <a href="https://ui.adsabs.harvard.edu/abs/1996ApJ...466L..63J/abstract">previously been seen</a>. Observations with a network of telescopes, including CSIRO’s 64-metre Parkes telescope and Australia Telescope Compact Array, had provided the most detailed images before now. </p>
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<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>
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<p>Our team used an international network of seven telescopes spanning North and South America and Antarctica. (Australia sadly doesn’t have the high-altitude observation sites necessary to make this kind of observation.)</p>
<p>The telescopes imaged the black hole’s jets in 16 times more detail than previous images. This revealed two things: first, and slightly surprisingly, nothing is seen in the vicinity of the black hole itself; and second, and even more intriguingly, only the outer edges of the jets seem to emit radiation. </p>
<p>While this “edge-brightening” has been seen for several other nearby active galaxies, this is the first time it has been seen in Centaurus A, and seen so clearly.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/411853/original/file-20210719-27-11057h.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Radioastronomy images of black hole plasma jets" src="https://images.theconversation.com/files/411853/original/file-20210719-27-11057h.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/411853/original/file-20210719-27-11057h.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=250&fit=crop&dpr=1 600w, https://images.theconversation.com/files/411853/original/file-20210719-27-11057h.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=250&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/411853/original/file-20210719-27-11057h.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=250&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/411853/original/file-20210719-27-11057h.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=314&fit=crop&dpr=1 754w, https://images.theconversation.com/files/411853/original/file-20210719-27-11057h.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=314&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/411853/original/file-20210719-27-11057h.jpeg?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"></a>
<figcaption>
<span class="caption">Left: the previous best image of the Centaurus A black hole’s plasma jets; middle: the new image; right: the larger plasma jets from M87’s black hole.</span>
<span class="attribution"><span class="source">Nature Astronomy</span></span>
</figcaption>
</figure>
<p>The edge of the jet may be brightened by the interaction of the jet plasma with the gas and dust in the galaxy. The narrowness of the jets also hints that strong magnetic fields may be coiled around the jet, and these may also lead to brighter edges and create an invisible “spine” to the jet. </p>
<p>The overall geometry and properties of the jet bear a striking resemblance to those of the jet in M87, as well as to jets launched by smaller black holes (tens of solar masses rather than millions or billions) in our own galaxy, the Milky Way. This supports the idea that the same processes happen in both supermassive black holes and their lighter counterparts, suggesting supermassive black holes are simply a scaled-up version of smaller ones, without requiring any new (or additional) physical mechanisms to be invoked.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/cosmic-jets-whats-shooting-out-of-black-holes-20155">Cosmic jets: what's shooting out of black holes?</a>
</strong>
</em>
</p>
<hr>
<p>As to why we saw nothing in the vicinity of the supermassive black hole itself, it is possible our line of sight is blocked by dense matter falling towards the black hole. We might be able to see more by increasing our observing frequency into the terahertz range, but that is a huge technical challenge.</p>
<p>COVID restrictions resulted in our 2020 observing campaign being abandoned, however the Event Horizon Telescope array was back in operation for a campaign in April this year, with further observations of M87 and Centaurus A on its list of targets. </p>
<p>Another source that has already been observed is the supermassive black hole at the centre of the Milky Way. Much closer than those of Centaurus A (15 million light years) or M87 (55 million light years), it is “only” 25,000 light years away, but it is also much less massive — roughly five million times the mass of our Sun. </p>
<p>While we believe this black hole has been <a href="https://theconversation.com/a-dormant-volcano-the-black-hole-at-the-heart-of-our-galaxy-is-more-explosive-than-we-thought-124696">active in the distant past</a>, recent observations have not revealed any bright jets emerging from the centre of our galaxy, suggesting it is not currently as active, but could potentially become active again in the future. It will be interesting to see what our forthcoming observations reveal.</p><img src="https://counter.theconversation.com/content/164709/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Phil Edwards 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>Astronomers have taken a close-up look at the jets of plasma streaking away from a supermassive black hole - one of the strangest and most energetic features of galaxies.Phil Edwards, Program Director, Australia Telescope National Facility Science, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1579182021-03-26T11:41:06Z2021-03-26T11:41:06ZWe’ve imaged a black hole’s magnetic field for the first time – here’s what it reveals<figure><img src="https://images.theconversation.com/files/391881/original/file-20210326-15-1pkaows.jpg?ixlib=rb-1.1.0&rect=0%2C5%2C3414%2C3403&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A black hole imaged in polarised light, revealing its magnetic fields.</span> <span class="attribution"><span class="source">EHT Collaboration</span></span></figcaption></figure><p>There was a lot of excitement when the <a href="https://theconversation.com/astronomers-to-peer-into-a-black-hole-for-first-time-with-new-event-horizon-telescope-74559">Event Horizon Telescope</a> collaboration showed the world the <a href="https://theconversation.com/first-black-hole-photo-confirms-einsteins-theory-of-relativity-115167">first ever image of a black hole back</a> in April 2019. Weighing in at 6.5 million times the mass of our Sun, this supermassive black hole is located in the <a href="https://www.nasa.gov/feature/goddard/2017/messier-87">galaxy Messier 87</a>, or M87, some 55 million light years away from Earth.</p>
<p>This was the first direct evidence that black holes exist. It also provided an extraordinary test of Einstein’s theory of gravity and its underlying notions of space and time – probing gravity in its most extreme limits. But we still don’t know much about these monsters. </p>
<p>Now, nearly two years on from this historical achievement, we have unveiled a new image of M87 using a different technique. Our research, published in two new papers in <a href="https://iopscience.iop.org/journal/2041-8205/page/Focus_on_EHT">The Astrophysical Journal Letters</a>, is providing important insights into the mysterious nature of black holes.</p>
<h2>Seeing the invisible</h2>
<p>Due to its distance from us, imaging this behemoth of a black hole is enormously challenging. It requires a resolution sharp enough to focus on an orange on the surface of the Moon, or being able to see individual atoms in one’s own finger. The telescope managed this thanks to an unprecedented collaboration between scientists across the globe, linking together <a href="https://eventhorizontelescope.org">eight ground-based radio telescopes</a> and transforming the Earth into one giant virtual radio telescope.</p>
<p>Black holes are perhaps the most enigmatic objects in nature, powering some of the most energetic – and unobservable – phenomena in our universe. Due to their event horizon, the boundary beyond which nothing, not even light, can escape, we cannot see a black hole directly. But matter that falls towards a black hole is drawn in by its immense gravitational pull and becomes extremely hot and luminous. </p>
<figure class="align-center ">
<img alt="First ever image of a black hole." src="https://images.theconversation.com/files/391893/original/file-20210326-21-1kkty6k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/391893/original/file-20210326-21-1kkty6k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/391893/original/file-20210326-21-1kkty6k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/391893/original/file-20210326-21-1kkty6k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/391893/original/file-20210326-21-1kkty6k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/391893/original/file-20210326-21-1kkty6k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/391893/original/file-20210326-21-1kkty6k.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">First ever image of a black hole.</span>
<span class="attribution"><span class="source">Event Horizon Telescope</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>As it approaches the event horizon, this matter is super heated by friction and moves close to the speed of light, emitting copious amounts of radiation. It is radiation in the form of radio waves produced by this gas moments before it crosses the event horizon that the telescope is designed to detect.</p>
<h2>New image</h2>
<p>The image of M87’s black hole provided overwhelming support for the idea that supermassive black holes lurk in the hearts of most (if not all) galaxies. They are the glue holding galaxies together and governing their dynamics and evolution. But exactly how they operate is unclear. </p>
<p>Our new image uses <a href="https://www.physicsclassroom.com/class/light/Lesson-1/Polarization">polarised light</a> – light waves oscillating in only one direction – produced by matter at the edge of the black hole. Unpolarised light is made up of light waves oscillating in many different directions. Light can become polarised if it moves through super hot regions of space that are highly magnetised. The strong magnetic fields present around the black hole are such regions and through studying the properties of this polarised light we can learn much more about the matter which produced it.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/6xrJoPjfJGQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Our new polarised image gives compelling new evidence for how strong magnetic fields around black holes can launch and sustain concentrated jets of charged gas over thousands of light years. We now think that such highly energetic and bright jets, launching enormous amounts of matter into the intergalactic medium, are connected to black holes through these strong magnetic fields.</p>
<p>Astronomers have invoked different models to explain how matter behaves near the black hole to better <a href="https://theconversation.com/how-we-discovered-the-strange-physics-of-jets-from-supermassive-black-holes-92390">understand this process of jet formation</a>, but they still do not know exactly how jets larger than the galaxy itself can be launched from its central region, nor how exactly matter falls into the black hole. We now find that only theoretical models featuring strongly magnetised matter can explain what is seen at the event horizon. </p>
<p>Our observations provide new, detailed information about the structure of the magnetic fields just outside the black hole. Not only does this bring us a step closer to understanding how these mysterious and powerful jets are produced, it also explains how some ultra hot matter can lurk outside a black hole, resisting its gravity. Our research suggests that the magnetic fields are strong enough to push back on the hot gas and help it resist gravity’s pull. Only the gas that slips through the field can start flowing inwards to the event horizon.</p>
<p>As exciting as these new polarised images of M87’s black hole are, it is still only the beginning for the Event Horizon Telescope collaboration and the science of black hole imaging. We are already working on what the image of the black hole that resides in the centre of our own Galaxy would look like, which we hope to publish later this year. This is <a href="https://www.nasa.gov/mission_pages/chandra/multimedia/black-hole-SagittariusA.html">Sagittarius A*</a>, or Sgr A*, our galaxy’s supermassive black hole. </p>
<p>Compared to M87, this new image is much more challenging to obtain. We are looking at the black hole through our blurry, turbulent interstellar medium – there’s a large amount of dust and gas in the way – making it significantly harder to take a clear picture. In the years to come, new telescopes will be added to the Event Horizon Telescope array, both on Earth, and eventually even in space, promising ever sharper images of black holes and providing a much more intimate understanding of these enigmatic entities.</p>
<p>There will be many more surprises in store. This is an exciting new era in humankind’s exploration of strong gravity and the nature of space and time, and undoubtedly the best is yet to come.</p><img src="https://counter.theconversation.com/content/157918/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ziri Younsi receives funding from the UKRI/STFC via a Stephen Hawking Fellowship and from the Leverhulme Trust via a Leverhulme Trust Early Career Fellowship.</span></em></p>New research can help explain how black holes can produce powerful jets.Ziri Younsi, UKRI Stephen Hawking Fellow, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1545632021-02-04T07:06:04Z2021-02-04T07:06:04ZThese distant ‘baby’ black holes seem to be misbehaving — and experts are perplexed<figure><img src="https://images.theconversation.com/files/382414/original/file-20210204-14-2u8inb.png?ixlib=rb-1.1.0&rect=0%2C0%2C5476%2C2311&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Dr Natasha Hurley-Walker (Curtin / ICRAR) and The GLEAM Team</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Radio images of the sky have revealed hundreds of “baby” and supermassive black holes in distant galaxies, with the galaxies’ light bouncing around in unexpected ways. </p>
<p>Galaxies are vast cosmic bodies, tens of thousands of light years in size, made up of gas, dust, and stars (like our Sun). </p>
<p>Given their size, you’d expect the amount of light emitted from galaxies would change slowly and steadily, over timescales far beyond a person’s lifetime. </p>
<p>But our research, <a href="https://academic.oup.com/mnras/article-abstract/501/4/6139/6031337?redirectedFrom=fulltext">published</a> in the Monthly Notices of the Royal Astronomical Society, found a surprising population of galaxies whose light changes much more quickly, in just a matter of years.</p>
<h2>What is a radio galaxy?</h2>
<p>Astronomers think there’s a supermassive black hole at the centre of most galaxies. Some of these are “active”, which means they emit a lot of radiation. </p>
<p>Their powerful gravitational fields pull in matter from their surroundings and rip it apart into an orbiting donut of hot plasma called an “accretion disk”.</p>
<p>This disk orbits the black hole at nearly the speed of light. Magnetic fields accelerate high-energy particles from the disk in long, thin streams or “jets” along the rotational axes of the black hole. As they get further from the black hole, these jets blossom into large mushroom-shaped clouds or “lobes”.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/382398/original/file-20210204-18-coa4jt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Radio galaxy with bright yellow core, long thin jets extending in opposite directions and large red lobes" src="https://images.theconversation.com/files/382398/original/file-20210204-18-coa4jt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/382398/original/file-20210204-18-coa4jt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=426&fit=crop&dpr=1 600w, https://images.theconversation.com/files/382398/original/file-20210204-18-coa4jt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=426&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/382398/original/file-20210204-18-coa4jt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=426&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/382398/original/file-20210204-18-coa4jt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=536&fit=crop&dpr=1 754w, https://images.theconversation.com/files/382398/original/file-20210204-18-coa4jt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=536&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/382398/original/file-20210204-18-coa4jt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=536&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 radio galaxy Hercules A has an active supermassive black hole at its centre. Here it is pictured emitting high energy particles in jets expanding out into radio lobes.</span>
<span class="attribution"><span class="source">NASA/ESA/NRAO</span></span>
</figcaption>
</figure>
<p>This entire structure is what makes up a radio galaxy, so called because it gives off a lot of radio-frequency radiation. It can be hundreds, thousands or even millions of light years across and therefore can take aeons to show any dramatic changes.</p>
<p>Astronomers have long questioned why some radio galaxies host enormous lobes, while others remain small and confined. Two theories exist. One is that the jets are held back by dense material around the black hole, often referred to as frustrated lobes. </p>
<p>However, the details around this phenomenon remain unknown. It’s still unclear whether the lobes are only temporarily confined by a small, extremely dense surrounding environment — or if they’re slowly pushing through a larger but less dense environment.</p>
<p>The second theory to explain smaller lobes is the jets are young and have not yet extended to great distances. </p>
<h2>Old ones are red, babies are blue</h2>
<p>Both young and old radio galaxies can be identified by a clever use of modern radio astronomy: looking at their “radio colour”.</p>
<p>We looked at data from the <a href="https://theconversation.com/what-the-universe-looks-like-when-viewed-with-radio-eyes-66381">GaLactic and Extragalactic All Sky MWA (GLEAM) survey</a>, which sees the sky at 20 different radio frequencies, giving astronomers an unparalleled “radio colour” view of the sky. </p>
<p>From the data, baby radio galaxies appear blue, which means they’re brighter at higher radio frequencies. Meanwhile the old and dying radio galaxies appear red and are brighter in the lower radio frequencies.</p>
<p>We identified 554 baby radio galaxies. When we looked at identical data taken a year later, we were surprised to see 123 of these were bouncing around in their brightness, appearing to flicker. This left us with a puzzle. </p>
<p>Something more than one light year in size can’t vary so much in brightness over less than one year without breaking the laws of physics. So, either our galaxies were far smaller than expected, or something else was happening. </p>
<p>Luckily, we had the data we needed to find out.</p>
<p>Past research on the variability of radio galaxies has used either a small number of galaxies, archival data collected from many different telescopes, or was conducted using only a single frequency. </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>
<p>For our research, we surveyed more than 21,000 galaxies over one year across multiple radio frequencies. This makes it the first “spectral variability” survey, enabling us to see how galaxies change brightness at different frequencies. </p>
<p>Some of our bouncing baby radio galaxies changed so much over the year we doubt they are babies at all. There’s a chance these compact radio galaxies are actually angsty teens rapidly growing into adults much faster than we expected.</p>
<p>While most of our variable galaxies increased or decreased in brightness by roughly the same amount across all radio colours, some didn’t. Also, 51 galaxies changed in both brightness <em>and</em> colour, which may be a clue as to what causes the variability.</p>
<h2>3 possibilities for what is happening</h2>
<p><strong>1) Twinkling galaxies</strong></p>
<p>As light from stars travels through Earth’s atmosphere, it is distorted. This creates the twinkling effect of stars we see in the night sky, called “scintillation”. The light from the radio galaxies in this survey passed through our Milky Way galaxy to reach our telescopes on Earth. </p>
<p>Thus, the gas and dust within our galaxy could have distorted it the same way, resulting in a twinkling effect. </p>
<p><strong>2) Looking down the barrel</strong></p>
<p>In our three-dimensional Universe, sometimes black holes shoot high energy particles directly towards us on Earth. These radio galaxies are called “blazars”. </p>
<p>Instead of seeing long thin jets and large mushroom-shaped lobes, we see blazars as a very tiny bright dot. They can show extreme variability in short timescales, since any little ejection of matter from the supermassive black hole itself is directed straight towards us. </p>
<p><strong>3) Black hole burps</strong></p>
<p>When the central supermassive black hole “burps” some extra particles they form a clump slowly travelling along the jets. As the clump propagates outwards, we can detect it first in the “radio blue” and then later in the “radio red”.</p>
<p>So we may be detecting giant black hole burps slowly travelling through space. </p>
<h2>Where to now?</h2>
<p>This is the first time we’ve had the technological ability to conduct a large-scale variability survey over multiple radio colours. The results suggest our understanding of the radio sky is lacking and perhaps radio galaxies are more dynamic than we expected. </p>
<figure class="align-center ">
<img alt="Artist's impression of the SKA: on the left multiple dishes scattered around representing SKA_MID and on the right a large collection of antennas representing SKA_LOW." src="https://images.theconversation.com/files/382417/original/file-20210204-18-kxrm5w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/382417/original/file-20210204-18-kxrm5w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/382417/original/file-20210204-18-kxrm5w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/382417/original/file-20210204-18-kxrm5w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/382417/original/file-20210204-18-kxrm5w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/382417/original/file-20210204-18-kxrm5w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/382417/original/file-20210204-18-kxrm5w.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">
<figcaption>
<span class="caption">An artist’s impression of the SKA telescope. On the left is SKA-Mid, fading into SKA-Low on the right.</span>
<span class="attribution"><span class="source">SKAO/ICRAR/SARAO</span></span>
</figcaption>
</figure>
<p>As the next generation of telescopes come online, in particular the Square Kilometre Array (SKA), astronomers will build up a dynamic picture of the sky over many years.</p>
<p>In the meantime, it’s worth watching these weirdly behaving radio galaxies and keeping a particularly close eye on the bouncing babies, too.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-worlds-oldest-story-astronomers-say-global-myths-about-seven-sisters-stars-may-reach-back-100-000-years-151568">The world's oldest story? Astronomers say global myths about 'seven sisters' stars may reach back 100,000 years</a>
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</em>
</p>
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<img src="https://counter.theconversation.com/content/154563/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kathryn Ross receives funding from the Australian Research Training Program (RTP), funded by the Australian Government. </span></em></p><p class="fine-print"><em><span>Dr Natasha Hurley-Walker is supported by an Australian Research Council Future Fellowship (project number FT190100231), funded by the Australian Government.</span></em></p>Some of the baby radio galaxies found may not be ‘babies’ at all. Rather, they may be ‘angsty teens’, rapidly growing into adults much faster than researchers had anticipated.Kathryn Ross, PhD Student, Curtin UniversityNatasha Hurley-Walker, Radio Astronomer, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1533642021-02-01T13:09:54Z2021-02-01T13:09:54ZCould a human enter a black hole to study it?<figure><img src="https://images.theconversation.com/files/381286/original/file-20210129-19-1ly38eg.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A person falling into a black hole and being stretched while approaching the black hole's horizon.</span> <span class="attribution"><span class="source">Leo Rodriguez and Shanshan Rodriguez</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Could a human enter a black hole to study it? – Pulkeet, age 12, Bahadurgarh, Haryana, India</strong></p>
</blockquote>
<hr>
<p>To solve the mysteries of black holes, a human should just venture into one. However, there is a rather complicated catch: A human can do this only if the respective black hole is supermassive and isolated, and if the person entering the black hole does not expect to report the findings to anyone in the entire universe. </p>
<p>We are <a href="https://www.grinnell.edu/user/rodriguezl">both</a> <a href="https://www.grinnell.edu/user/rodriguezs">physicists</a> who study black holes, albeit from a very safe distance. Black holes are <a href="https://doi.org/10.1093/mnras/stx1959">among the most abundant astrophysical objects in our universe</a>. These intriguing objects appear to be an essential ingredient in the <a href="https://link.springer.com/chapter/10.1007%2F978-3-642-39596-3_8">evolution of the universe</a>, from the Big Bang till present day. They probably had an <a href="https://doi.org/10.1093/mnras/stz2161">impact on the formation of human life in our own galaxy</a>. </p>
<h2>Two types of black holes</h2>
<p>The universe is littered with a <a href="https://www.washingtonpost.com/science/2019/11/29/scientists-find-monster-black-hole-so-big-they-didnt-think-it-was-possible/">vast zoo of different types of black holes</a>. </p>
<p>They can vary by size and be electrically charged, the same way electrons or protons are in atoms. Some black holes actually spin. There are two types of black holes that are relevant to our discussion. The first does not rotate, is electrically neutral – that is, not positively or negatively charged – and has the mass of our Sun. The second type is a supermassive black hole, with a mass of millions to even billions times greater than that of our Sun. </p>
<p>Besides the mass difference between these two types of black holes, what also differentiates them is the distance from their center to their “event horizon” – a measure called radial distance. The event horizon of a black hole is the point of no return. Anything that passes this point will be swallowed by the black hole and forever vanish from our known universe. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/379201/original/file-20210118-13-1j8ys1.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/379201/original/file-20210118-13-1j8ys1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/379201/original/file-20210118-13-1j8ys1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=598&fit=crop&dpr=1 600w, https://images.theconversation.com/files/379201/original/file-20210118-13-1j8ys1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=598&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/379201/original/file-20210118-13-1j8ys1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=598&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/379201/original/file-20210118-13-1j8ys1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=752&fit=crop&dpr=1 754w, https://images.theconversation.com/files/379201/original/file-20210118-13-1j8ys1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=752&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/379201/original/file-20210118-13-1j8ys1.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"></a>
<figcaption>
<span class="caption">The distance from a black hole’s center of mass to where gravity’s pull is too strong to overcome is called the event horizon.</span>
<span class="attribution"><span class="source">Leo and Shanshan</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>At the event horizon, the black hole’s gravity is so powerful that no amount of mechanical force can overcome or counteract it. <a href="https://doi.org/10.1088/2053-2571/ab06bd">Even light</a>, the fastest-moving thing in our universe, cannot escape – hence the term “black hole.”</p>
<p>The radial size of the event horizon depends on the mass of the respective black hole and is key for a person to survive falling into one. For a black hole with a mass of our Sun (one solar mass), the event horizon will have a radius of just under 2 miles. </p>
<p>The supermassive black hole at the center of our Milky Way galaxy, by contrast, has a mass of roughly 4 million solar masses, and it has an event horizon with a radius of 7.3 million miles or 17 solar radii. </p>
<p>Thus, someone falling into a stellar-size black hole will get much, much closer to the black hole’s center before passing the event horizon, as opposed to falling into a supermassive black hole. </p>
<p>This implies, due to the closeness of the black hole’s center, that the black hole’s pull on a person will differ by a factor of 1,000 billion times between head and toe, depending on which is leading the free fall. In other words, if the person is falling feet first, as they approach the event horizon of a stellar mass black hole, the gravitational pull on their feet will be exponentially larger compared to the black hole’s tug on their head. </p>
<p>The person would experience spaghettification, and most likely not survive being stretched into a long, thin noodlelike shape.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/379434/original/file-20210119-21-1lb26xu.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/379434/original/file-20210119-21-1lb26xu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/379434/original/file-20210119-21-1lb26xu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=383&fit=crop&dpr=1 600w, https://images.theconversation.com/files/379434/original/file-20210119-21-1lb26xu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=383&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/379434/original/file-20210119-21-1lb26xu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=383&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/379434/original/file-20210119-21-1lb26xu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/379434/original/file-20210119-21-1lb26xu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/379434/original/file-20210119-21-1lb26xu.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"></a>
<figcaption>
<span class="caption">As the person approaches the event horizon of a a Sun-size black hole, the vast difference in gravitational pull between the inidvidual’s head and toes causes the person to stretch into a very long noodle, hence the term ‘spaghettification’.</span>
<span class="attribution"><span class="source">Leo and Shanshan Rodriguez</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Now, a person falling into a supermassive black hole would reach the event horizon much farther from the the central source of gravitational pull, which means that the difference in gravitational pull between head and toe is nearly zero. Thus, the person would pass through the event horizon unaffected, not be stretched into a long, thin noodle, survive and float painlessly past the black hole’s horizon.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/379435/original/file-20210119-24-1w07b7a.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/379435/original/file-20210119-24-1w07b7a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/379435/original/file-20210119-24-1w07b7a.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=566&fit=crop&dpr=1 600w, https://images.theconversation.com/files/379435/original/file-20210119-24-1w07b7a.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=566&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/379435/original/file-20210119-24-1w07b7a.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=566&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/379435/original/file-20210119-24-1w07b7a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=711&fit=crop&dpr=1 754w, https://images.theconversation.com/files/379435/original/file-20210119-24-1w07b7a.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=711&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/379435/original/file-20210119-24-1w07b7a.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=711&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 person falling into a supermassive black hole would likely survive.</span>
<span class="attribution"><span class="source">Leo and Shanshan Rodriguez</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Other considerations</h2>
<p>Most black holes that we observe in the universe are surrounded by very hot disks of material, mostly comprising gas and dust or other objects like stars and planets that got too close to the horizon and fell into the black hole. These disks are called accretion disks and are very hot and turbulent. They are most certainly not hospitable and would make traveling into the black hole extremely dangerous. </p>
<p>To enter one safely, you would need to find a supermassive black hole that is completely isolated and not feeding on surrounding material, gas and or even stars. </p>
<p>Now, if a person found an isolated supermassive black hole suitable for scientific study and decided to venture in, everything observed or measured of the black hole interior would be confined within the black hole’s event horizon.</p>
<p>Keeping in mind that nothing can escape the gravitational pull beyond the event horizon, the in-falling person would not be able to send any information about their findings back out beyond this horizon. Their journey and findings would be lost to the rest of the entire universe for all time. But they would enjoy the adventure, for as long as they survived … maybe ….</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/153364/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 organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>If you are a sci-fi junkie you’ve probably wondered what would happen if you were unlucky enough to fall into a black hole. How well you’d fare all depends on the type of black hole.Leo Rodriguez, Assistant Professor of Physics, Grinnell CollegeShanshan Rodriguez, Assistant Professor of Physics, Grinnell CollegeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1476132020-10-07T14:10:07Z2020-10-07T14:10:07ZNobel prize: how Penrose, Genzel and Ghez helped put black holes at the centre of modern astrophysics<figure><img src="https://images.theconversation.com/files/362191/original/file-20201007-18-1n7iqp3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/nustar/multimedia/pia16695.html">NASA/JPL-Caltech</a></span></figcaption></figure><p>The award of this year’s Nobel prize in physics to Roger Penrose, Reinhard Genzel and Andrea Ghez will be greeted with enormous pleasure by physicists and astronomers worldwide. It recognises the central importance of black holes in modern astrophysics, and the unique contributions of these three scientists in establishing this.</p>
<p>The physics that describes black holes comes from Einstein’s general theory of relativity (usually abbreviated to GR). GR is a little over a century old, and was from the start seen as a theory of unprecedented mathematical complication.</p>
<p>After some early successes, such as the observation that the paths of starlight bent under gravity as they passed near the Sun, the huge algebraic complexity of GR rapidly made it a backwater of physics. Laboriously derived solutions of Einstein’s equations found no practical application for experiments to test the theory. </p>
<p>Although one of these solutions hinted at properties we now know were characteristic of black holes, these were not understood at the time. And, in any case, they were often dismissed as artificial products of assumptions made for mathematical convenience. There seemed little hope of experimental tests that would reveal large and fundamentally new effects of GR.</p>
<p>Penrose is the theoretical physicist who made the crucial discovery that began the resurrection of GR theory from this apparent impasse to its dynamic state today, where its predictions – particularly about black holes – are constantly tested and verified.</p>
<p>Genzel and Ghez are the two astronomers whose observing teams independently verified the most extravagant prediction of GR by showing that our own galaxy, the Milky Way, has at its heart an enormously massive black hole described in intricate detail by the theory.</p>
<p>Penrose’s fundamental insight was that GR specifies physical causality: no physical effect can travel faster than light, and gravity bends light and determines how it moves. And in particular, gravity always attracts and never repels. In 1965, <a href="http://quantum-gravitation.de/media/2d2cde3ec9c38fffffff80d0fffffff1.pdf">he showed</a> that these properties alone make the objects we now call black holes an inescapable consequence of GR. </p>
<p>A crucial feature of this fundamental result is that it does not assume any geometrical symmetries in the matter that will eventually collapse under its own gravity to form a black hole. It need not be perfectly spherical, for example. Any misshapen collection of matter will end as a black hole if it has passed what Penrose identified as its point of no return, as it first traps light around itself. </p>
<p>In later years, <a href="https://books.google.co.uk/books?id=iGmPBAAAQBAJ&pg=PT312&lpg=PT312&dq=#v=onepage&q&f=false">he recalled</a> implicitly recognising this crucial point while crossing a London street in the company of the engaging fellow physicist Ivor Robinson, and being so taken by their conversation that he could not at first recall just what had made him feel so happy on crossing the street. </p>
<p>I can well remember the shock of realising how utterly new this approach was as a young PhD student of GR a few years later. It bypassed the complexity of solving the GR equations, and its completely general methods forced astrophysicists to take seriously the idea of black holes as potentially observable objects. </p>
<p>We now know, for example, of many stellar binary systems where one of the stars has collapsed to form a black hole, a discovery that led to a share of the 2002 Nobel Prize <a href="https://www.nobelprize.org/prizes/physics/2002/giacconi/lecture/">for Riccardo Giacconi</a>.</p>
<h2>Supermassive discovery</h2>
<p><a href="https://www.nature.com/articles/383415a0">Genzel</a> and <a href="https://iopscience.iop.org/article/10.1086/306528">Ghez</a> lead research groups that have independently shown that there is a much more massive black hole at the centre of the Milky Way. They did this by observing the motions of stars around this invisible object. </p>
<p>Years of painstaking observation by both groups reveal a <a href="http://www.astro.ucla.edu/%7Eghezgroup/gc/animations.html">rich pattern</a> of about 40 stars orbiting with different periods, eccentricities and inclinations on the sky. Each of these orbits tells us the mass of the object whose gravity pulls on them, and all of them agree on a single huge value about 4 million times that of the Sun. But evidence from radio waves emitted near the object indicates that it is remarkably small, strongly suggesting that it must be a black hole.</p>
<p><a href="https://www.aanda.org/articles/aa/full_html/2020/04/aa37813-20/aa37813-20.html">Recent observations</a> reveal that the orbits of the closest stars to the galactic centre are not quite perfect ellipses, but slowly move to trace out rosettes on the sky. This is precisely what GR predicts for very close orbits around a black hole. The independent but almost identical results of the two groups leave very little room for doubt that this is our own local supermassive black hole. </p>
<p>The consequences are profound, and I am just one of many astrophysicists studying them. Observations strongly suggest that the centre of almost every galaxy has its own supermassive black hole – many of them far more massive than in the Milky Way – and that these masses are closely related to detailed properties of the host galaxies. These supermassive black holes evidently play a major role in making galaxies as they are, creating the architecture of the universe we live in.</p><img src="https://counter.theconversation.com/content/147613/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew King has received funding from the UK Science and Technology Research Council for research in astrophysics. </span></em></p>Roger Penrose helped resurrect Einstein’s general theory of relativity, and Reinhard Genzel and Andrea Ghez showed there was a black hole in the middle of our galaxy.Andrew King, Professor of Astrophysics, University of LeicesterLicensed 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/1282952019-12-12T13:19:28Z2019-12-12T13:19:28ZSupermassive black hole at the center of our galaxy may have a friend<figure><img src="https://images.theconversation.com/files/305904/original/file-20191209-90609-1b1921c.jpg?ixlib=rb-1.1.0&rect=0%2C4%2C1041%2C579&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's conception of two black holes entwined in a gravitational tango.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/jpl/wise/black-holes-20131203i.html">NASA/JPL-Caltech/SwRI/MSSS/Christopher Go</a></span></figcaption></figure><p>Do supermassive black holes have friends? The nature of galaxy formation suggests that the answer is yes, and in fact, pairs of supermassive black holes should be common in the universe. </p>
<p><a href="http://www.astro.ucla.edu/%7Esnaoz/">I am an astrophysicist</a> and am interested in a wide range of theoretical problems in astrophysics, from the formation of the very first galaxies to the gravitational interactions of black holes, stars and even planets. Black holes are intriguing systems, and supermassive black holes and the dense stellar environments that surround them represent one of the most extreme places in our universe.</p>
<p>The supermassive black hole that lurks at the center of our galaxy, called Sgr A*, has a mass of about 4 million times that of our Sun. A black hole is a place in space where gravity is so strong that neither particles or light can escape from it. Surrounding Sgr A* is a dense cluster of stars. Precise measurements of the orbits of these stars allowed astronomers to confirm the existence of this supermassive black hole and to <a href="https://doi.org/10.1038/35030032">measure its mass</a>. For more than 20 years, scientists have been monitoring the orbits of these stars around the supermassive black hole. Based on what we’ve seen, <a href="https://arxiv.org/abs/1912.04910">my colleagues and I show</a> that if there is a friend there, it might be a <a href="https://doi.org/10.1126/science.aav8137">second black hole nearby</a> that is at least 100,000 times the mass of the Sun. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/305899/original/file-20191209-90580-1idoa91.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/305899/original/file-20191209-90580-1idoa91.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/305899/original/file-20191209-90580-1idoa91.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/305899/original/file-20191209-90580-1idoa91.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/305899/original/file-20191209-90580-1idoa91.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/305899/original/file-20191209-90580-1idoa91.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/305899/original/file-20191209-90580-1idoa91.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/305899/original/file-20191209-90580-1idoa91.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">At the center of our galaxy is a supermassive black hole in the region known as Sagittarius A. It has a mass of about 4 million times that of our Sun.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/herschel/multimedia/pia17009.html">ESA–C. Carreau</a></span>
</figcaption>
</figure>
<h2>Supermassive black holes and their friends</h2>
<p>Almost every galaxy, including our Milky Way, has a supermassive black hole at its heart, with masses of millions to billions of times the mass of the Sun. Astronomers are <a href="https://doi.org/10.1007/s00159-010-0029-x">still studying why the heart of galaxies</a> often hosts a supermassive black hole. One popular idea connects to the possibility that supermassive holes have friends. </p>
<p>To understand this idea, we need to go back to when the universe was about 100 million years old, to the era of the very first galaxies. They were much smaller than today’s galaxies, about 10,000 or more times less massive than the Milky Way. Within these early galaxies the very first stars that died created black holes, of about tens to thousand the mass of the Sun. These black holes sank to the center of gravity, the heart of their host galaxy. Since galaxies evolve by merging and colliding with one another, collisions between galaxies will result in supermassive black hole pairs – the key part of this story. The black holes then collide and grow in size as well. A black hole that is more than a million times the mass of our son is considered supermassive. </p>
<p>If indeed the supermassive black hole has a friend revolving around it in close orbit, the center of the galaxy is locked in a complex dance. The partners’ gravitational tugs will also exert its own pull on the nearby stars disturbing their orbits. The two supermassive black holes are orbiting each other, and at the same time, each is exerting its own pull on the stars around it. </p>
<p>The gravitational forces from the black holes pull on these stars and make them change their orbit; in other words, after one revolution around the supermassive black hole pair, a star will not go exactly back to the point at which it began. </p>
<p>Using our understanding of the gravitational interaction between the possible supermassive black hole pair and the surrounding stars, astronomers can predict what will happen to stars. Astrophysicists like my colleagues and me can compare our predictions to observations, and then can determine the possible orbits of stars and figure out whether the supermassive black hole has a companion that is exerting gravitational influence. </p>
<p>Using a well-studied star, called S0-2, which orbits the supermassive black hole that lies at the center of the galaxy every 16 years, we can already rule out the idea that there is a second supermassive black hole with mass above 100,000 times the mass of the Sun and farther than about 200 times the distance between the Sun and the Earth. If there was such a companion, then I and my colleagues would have detected its effects on the orbit of SO-2. </p>
<p>But that doesn’t mean that a smaller companion black hole cannot still hide there. Such an object may not alter the orbit of SO-2 in a way we can easily measure.</p>
<h2>The physics of supermassive black holes</h2>
<p>Supermassive black holes have gotten a lot of attention lately. In particular, the <a href="https://doi.org/10.3847/2041-8213/ab0e85">recent image</a> of such a giant at the center of the galaxy M87 opened a new window to understanding the physics behind black holes. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/306254/original/file-20191211-95165-13uu1j6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/306254/original/file-20191211-95165-13uu1j6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/306254/original/file-20191211-95165-13uu1j6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/306254/original/file-20191211-95165-13uu1j6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/306254/original/file-20191211-95165-13uu1j6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/306254/original/file-20191211-95165-13uu1j6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/306254/original/file-20191211-95165-13uu1j6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/306254/original/file-20191211-95165-13uu1j6.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">The first image of a black hole. This is the supermassive black hole at the center of the galaxy M87.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/news/news.php?feature=7372">Event Horizon Telescope Collaboration</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The proximity of the Milky Way’s galactic center – a mere 24,000 light-years away – provides a unique laboratory for addressing issues in the fundamental physics of supermassive black holes. For example, astrophysicists like myself would like to understand their impact on the central regions of galaxies and their role in galaxy formation and evolution. The detection of a pair of supermassive black holes in the galactic center would indicate that the Milky Way merged with another, possibly small, galaxy at some time in the past. </p>
<p>That’s not all that monitoring the surrounding stars can tell us. Measurements of the star S0-2 allowed scientists to carry out a unique test of Einstein’s general theory of relativity. In May 2018, S0-2 zoomed past the supermassive black hole at a distance of only about 130 times the Earth’s distance from the Sun. According to Einstein’s theory, the wavelength of light emitted by the star should stretch as it climbs from the deep gravitational well of the supermassive black hole. </p>
<p>The stretching wavelength that Einstein predicted – which makes the star appear redder – was detected and proves that the theory of general relativity <a href="http://doi.org/10.1126/science.aav8137">accurately describes the</a> <a href="http://doi.org/10.1051/0004-6361/201833718">physics in this extreme gravitational</a> zone. I am eagerly awaiting the second closest approach of S0-2, which will occur in about 16 years, because astrophysicists like myself will be able to test more of Einstein’s predictions about general relativity, including the change of the orientation of the stars’ elongated orbit. But if the supermassive black hole has a partner, this could alter the expected result. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/305933/original/file-20191209-90580-1aqmixh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/305933/original/file-20191209-90580-1aqmixh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/305933/original/file-20191209-90580-1aqmixh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=273&fit=crop&dpr=1 600w, https://images.theconversation.com/files/305933/original/file-20191209-90580-1aqmixh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=273&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/305933/original/file-20191209-90580-1aqmixh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=273&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/305933/original/file-20191209-90580-1aqmixh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=344&fit=crop&dpr=1 754w, https://images.theconversation.com/files/305933/original/file-20191209-90580-1aqmixh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=344&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/305933/original/file-20191209-90580-1aqmixh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=344&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 NASA/ESA Hubble Space Telescope image show’s the result of a galactic collision between two good-sized galaxies. This new jumble of stars is slowly evolving to become a giant elliptical galaxy.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/goddard/2016/hubble-views-a-galactic-mega-merger">ESA/Hubble & NASA, Acknowledgement: Judy Schmidt</a></span>
</figcaption>
</figure>
<p>Finally, if there are two massive black holes orbiting each other at the galactic center, as my team suggests is possible, they will emit <a href="https://www.ligo.caltech.edu/page/what-are-gw">gravitational waves</a>. Since 2015, the <a href="https://www.ligo.caltech.edu/">LIGO-Virgo</a> observatories have been detecting gravitational wave radiation from merging stellar-mass black holes and neutron stars. These groundbreaking detections have opened a new way for scientists to sense the universe. </p>
<p>Any waves emitted by our hypothetical black hole pair will be at low frequencies, too low for the LIGO-Virgo detectors to sense. But a planned space-based detector known as <a href="https://lisa.nasa.gov/">LISA</a> may be able to detect these waves which will help astrophysicists figure out whether our galactic center black hole is alone or has a partner.</p>
<p>[ <em>Like what you’ve read? Want more?</em> <a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=likethis">Sign up for The Conversation’s daily newsletter</a>. ]</p><img src="https://counter.theconversation.com/content/128295/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Smadar Naoz receives funding from NSF, NASA, Sloan and Keck foundations. </span></em></p>There is a massive black hole in the center of the Milky Way galaxy. Measurements of star orbits near this black hole suggest that there may be a second companion black hole nearby.Smadar Naoz, Associate Professor of Physics & Astronomy, University of California, Los AngelesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1246962019-10-08T00:45:18Z2019-10-08T00:45:18ZA dormant volcano: the black hole at the heart of our galaxy is more explosive than we thought<figure><img src="https://images.theconversation.com/files/295549/original/file-20191004-52826-ca09mr.jpg?ixlib=rb-1.1.0&rect=8%2C0%2C1894%2C1077&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Conical jets of radiation burst from the black hole at the centre of the Milky Way</span> <span class="attribution"><span class="source">Joss Bland-Hawthorn</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The supermassive black hole at the heart of our Galaxy spat out an enormous flare of radiation 3.5 million years ago that would have been clearly visible from Earth.</p>
<p>In <a href="https://arxiv.org/abs/1910.02225">new research</a> that will soon be published in the <em>Astrophysical Journal</em> my colleagues and I found that the flare left traces in a trail of gas called the Magellanic Stream that lies some 200,000 light years away and encircles the Milky Way. </p>
<p>The team includes Ralph Sutherland and Brent Groves at the Australian National University and ASTRO-3D; Magda Guglielmo, Wen Hao Li and Andrew Curzons at the University of Sydney; Philip Maloney at the University of Colorado; Gerald Cecil at the University of Carolina; and Andrew J. Fox at the Space Telescope Science Institute in Baltimore.</p>
<p>The discovery changes our view of our galaxy’s central black hole, which has appeared dormant throughout recorded human history. Astronomers are coming to realise that it has been hugely active, even explosive, in the relatively recent past in galactic terms (measured in millions of years). </p>
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<figcaption><span class="caption">Radiation flashes out from the hot spinning gas around the supermassive black hole at the centre of the Milky Way, leaving traces in the Magellanic Stream. Credit: James Josephides / Swinburne University.</span></figcaption>
</figure>
<p>This activity has been flickering on and off for billions of years. We don’t understand why this activity is intermittent, but it has something to do with how material gets dumped onto the black hole. It might be like water droplets on a hot plate that sputter and explode chaotically, depending on their size.</p>
<p>Our situation on Earth resembles living near a largely dormant volcano like Mount Vesuvius that is known to have been explosively active in the past, with disastrous consequences for Pompeii. </p>
<p>Despite this, there’s no need to be alarmed: as far as we can tell, we are safe here in orbit about a cool dwarf star far from the centre of the Milky Way. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/295569/original/file-20191004-118217-n5mcrg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/295569/original/file-20191004-118217-n5mcrg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/295569/original/file-20191004-118217-n5mcrg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=460&fit=crop&dpr=1 600w, https://images.theconversation.com/files/295569/original/file-20191004-118217-n5mcrg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=460&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/295569/original/file-20191004-118217-n5mcrg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=460&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/295569/original/file-20191004-118217-n5mcrg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=578&fit=crop&dpr=1 754w, https://images.theconversation.com/files/295569/original/file-20191004-118217-n5mcrg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=578&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/295569/original/file-20191004-118217-n5mcrg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=578&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 bright area in the lower left is the centre of the galaxy. Only the densest clouds of dust can be seen in this infrared image.</span>
<span class="attribution"><a class="source" href="https://old.ipac.caltech.edu/2mass/gallery/showcase/galcen/index.html">Atlas / 2MASS / University of Massachusetts / California Institute of Technology</a></span>
</figcaption>
</figure>
<h2>Why is there a black hole at the centre of the galaxy?</h2>
<p>If you look along the Milky Way in the direction of the constellation Sagittarius, you will see the dense agglomeration of stars around the centre of the galaxy. The galactic centre is marked by a very dense, very massive cluster of stars orbiting the supermassive black hole. </p>
<p>Earlier this year, the ESO Gravity team found a star close to the black hole travelling at up to 10,000 km per second, a few percent of the speed of light. This let them weigh the black hole to a precision of 1%, arriving at a number of about 4 million times the Sun’s mass. </p>
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<strong>
Read more:
<a href="https://theconversation.com/einsteins-theory-of-gravity-tested-by-a-star-speeding-past-a-supermassive-black-hole-100658">Einstein’s theory of gravity tested by a star speeding past a supermassive black hole</a>
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<p>As galactic supermassive black holes go, this is a featherweight. For example, our neighbouring galaxy Andromeda also has a supermassive black hole, but it is 50 times heavier than ours. </p>
<p>Essentially all large galaxies have central massive black holes. We don’t know exactly why this is so, but we know it’s important and that the growth phases of these monsters are likely to have affected the galaxy as a whole. </p>
<p>Understanding the effect of interactions between black holes and host galaxies is one of the hottest topics in modern astrophysics.</p>
<h2>Some black holes are more active than others</h2>
<p>But if we look out across the Universe, we see only a few percent of galaxies appear to have “active” black holes. By active, we mean that gas and stars spiralling into the black hole form an extremely hot ring of gas. </p>
<p>This ring, called an accretion disc, gets so hot that it drives jets, winds and radiating beams of light out across the galaxy. The effects of these explosions are particularly impressive in more massive galaxies. </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>
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<p>For decades, Australian radio telescopes have mapped out jet flows that are far larger than the visible galaxy in the middle. </p>
<p>The radio jets in the galaxy Centaurus A extend more than 10 degrees across the sky – that’s the size of 20 full moons next to each other. This is remarkable given Centaurus A is 10 million light years away.</p>
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<span class="caption">An enhanced radio image of Centaurus A. The inset picture zooms in on the jets coming from the central black hole.</span>
<span class="attribution"><span class="source">CSIRO/ATNF; ATCA;ASTRON; Parkes;MPIfR; ESO/WFI/AAO (UKST); MPIfR/ESO/APEX; NASA/CXC/CfA</span></span>
</figcaption>
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<h2>The Milky Way explosion</h2>
<p>Some three million years ago, our direct ancestor <em>Australopithecus afarensis</em> walked the Earth. They may well have looked up towards Sagittarius and seen cones of light shooting sideways from the Milky Way, brighter than any star in the night sky. </p>
<p>The lightshow would have appeared as static beams on a human timescale, only flickering on timescales of thousands of years. Today, the only visible remnant of that immensely powerful event is the cooling gas along the distant Magellanic Stream.</p>
<p>So how would life on Earth have fared if the explosive jet was directed straight at us? This is a valid question, because we believe that the spin axis of the accretion disc flops around wildly in lightweight supermassive black holes. </p>
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<figcaption><span class="caption">The beams of radiation from the black hole’s accretion disk flop around in different directions over thousands of years. Credit: Phil Hopkins / Caltech.</span></figcaption>
</figure>
<p>If the beam was pointing at the Solar System, the jet would have to plough through the Milky Way disc, and it would take about ten million years to reach us.</p>
<p>So it’s possible that a more ancient explosion could have produced a powerful jet that is yet to reach us. </p>
<p>But we need not worry – at its peak, the intensity of the jet when it reaches us is unlikely to exceed the most energetic solar flares. These are known to knock out satellites, and pose a threat to space-walking astronauts, but our own atmosphere largely protects us on Earth.</p><img src="https://counter.theconversation.com/content/124696/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joss Bland-Hawthorn receives funding from the Australian Research Council, in particular, an Australian Laureate Fellowship. Joss is a CI for the ARC funded Centre of Excellence ASTRO-3D and is Director of the Sydney Institute for Astronomy, University of Sydney. </span></em></p>New research shows the supermassive black hole at the centre of the Milky Way spat out an enormous beam of radiation 3.5 million years agoJoss Bland-Hawthorn, Director, Sydney Institute for Astronomy, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1181812019-07-31T03:05:43Z2019-07-31T03:05:43ZCurious Kids: can Earth be affected by a black hole in the future?<figure><img src="https://images.theconversation.com/files/285998/original/file-20190729-43118-o01vq2.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C7283%2C4852&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Another reason you don’t want to get too close to a black hole is because of something we call 'spaghettification'. If this happened to Earth it would be... unpleasant. </span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em>If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au.</em> </p>
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<p><strong>Can Earth be affected by a black hole in the future? – Rakovi, age 12, Dimapur, India.</strong></p>
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<p>That is a great question.</p>
<p>As you know, black holes are called that because the gravity in their centre is so strong, it sucks all nearby light in. None can escape. That’s how strong a black’s hole’s gravitational pull is. </p>
<p>Black holes create the strongest gravitational pull in the universe (that we know of). So you really don’t want to get very close to one. </p>
<p>If you get too close, the pull of gravity from the black hole is so strong that you would never be able to escape, even if you were travelling at the speed of light. </p>
<p>This point of no return is called “the event horizon”. </p>
<p>Another reason you don’t want to get too close to a black hole is because of something we call “spaghettification”. </p>
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Read more:
<a href="https://theconversation.com/curious-kids-how-do-wormholes-work-90627">Curious Kids: How do wormholes work?</a>
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<p><img width="100%" src="https://media.giphy.com/media/Is0kQNjdkdppm/giphy.gif"></p>
<h2>Turning a star into spaghetti strips</h2>
<p>Imagine an object in space, like a star. As the star gets closer to a black hole, one side of it is pulled harder than the other. That’s because one side of the star will be closer to the black hole than the other. </p>
<p>The pull from gravity will be stronger on the side closest to the black hole, and weaker on the side that’s further away.</p>
<p>This difference in the pull of gravity (which is called a “tidal force”) would cause the star to get pulled apart. It’s kind of like pulling a lump of pasta dough into spaghetti. </p>
<p>Sometimes astronomers can observe this happening in other galaxies. The technical name is a “tidal disruption event” but it just means that a star got too close to a black hole and got pulled apart. </p>
<p>Here’s an artist’s impression of what spaghettification might look like: </p>
<p><img width="100%" src="https://media.giphy.com/media/uXjFFsHu683bG/giphy.gif"></p>
<h2>The closest black hole is too far away to hurt us</h2>
<p>Thankfully, though, we don’t need to worry. There are no black holes close enough to Earth to affect us. The closest black hole to Earth that we know of is named V616 Monocerotis. It is also known as <a href="https://en.wikipedia.org/wiki/A0620-00">A0620-00</a>.</p>
<p>This black hole is 6.6 times more massive than our Sun. (That means it has a <a href="https://theconversation.com/explainer-what-is-mass-49299">lot of mass</a>, which means it has a really strong gravitational pull – much stronger than even our Sun’s gravitational pull.)</p>
<p>If Earth gets within about 800,000 kilometres (3.7 light seconds) of this black hole it will get pulled apart. But that’s unlikely to happen and certainly not in your lifetime. </p>
<p>V616 Monocerotis is about 3,300 light years away. That’s very, very far away.</p>
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<p>
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<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>
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<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au</em></p><img src="https://counter.theconversation.com/content/118181/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Janie Hoormann receives funding from the Australian Research Council.</span></em></p>If you got too close to a black hole, it would suck you in and you’d never be able to escape, even if you were travelling at the speed of light.
This point of no return is called the event horizon.Janie Hoormann, Postdoctoral Research Fellow, Astrophysics, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1150642019-04-10T23:46:45Z2019-04-10T23:46:45ZObserving the invisible: the long journey to the first image of a black hole<figure><img src="https://images.theconversation.com/files/268696/original/file-20190410-2921-19jg4e0.jpg?ixlib=rb-1.1.0&rect=863%2C436%2C1670%2C1063&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The first direct visual evidence of the supermassive black hole in the centre of galaxy Messier 87 and its shadow.</span> <span class="attribution"><a class="source" href="https://www.eso.org/public/images/eso1907a/">EHT Collaboration</a></span></figcaption></figure><p>The first picture of a supermassive black hole at the centre of a galaxy shows how we have, in a sense, observed the invisible.</p>
<p>The <a href="https://www.eso.org/public/images/eso1907a/">ghostly image</a> is a radio intensity map of the glowing plasma behind, and therefore silhouetting, the black hole’s “<a href="http://astronomy.swin.edu.au/cosmos/E/Event+Horizon">event horizon</a>” — the spherical cloak of invisibility around a black hole from which not even light can escape.</p>
<p>The radio “photograph” was obtained by an international collaboration involving more than 200 scientists and engineers who linked some of the world’s most capable radio telescopes to effectively see the supermassive black hole in the galaxy known as M87.</p>
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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>
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<p>So how on Earth did we get to this point?</p>
<h2>From ‘dark stars’</h2>
<p>It was the English astronomer <a href="https://www.britannica.com/biography/John-Michell">John Michell</a> who in 1783 first formulated the idea of “dark stars” so incredibly dense that their gravity would be impossible to run from — even if you happened to be a photon able to move at the speed of light. </p>
<p>Things have come a long way since that pioneering insight.</p>
<p>In January this year, astronomers <a href="http://adsabs.harvard.edu/abs/2019ApJ...871...30I" title="The Size, Shape, and Scattering of Sagittarius A* at 86 GHz: First VLBI with ALMA">published an image</a> of the emission coming from the radio source known as Sagittarius A*, the region immediately surrounding the <a href="http://astronomy.swin.edu.au/cosmos/S/Supermassive+Black+Hole">supermassive black hole</a> at the centre of our galaxy.</p>
<p>Impressively, that image had detail on scales down to just nine times the size of the black hole’s event horizon.</p>
<p>Now, the Event Horizon Telescope (<a href="https://eventhorizontelescope.org/">EHT</a>) has succeeded in resolving the event horizon around the supermassive black hole in M87, a relatively nearby galaxy from which light takes 55 million light years to reach us, due to its distance.</p>
<h2>Astronomical figures</h2>
<p>Astronomical objects come with astronomical figures, and this target is no exception. </p>
<p>M87’s black hole has a mass that is 6.5 billion times that of our Sun, which itself is one-third of a million times the mass of the Earth. Its event horizon has a radius of roughly 20 billion kilometres, more than three times the distance Pluto is from our Sun. </p>
<p>It is, however, far away, and the incredible engineering feat required to see such a target is akin to trying to observe an object 1mm in size from a distance of 13,000km.</p>
<p>This Nobel Prize-worthy result is, of course, no accidental discovery, but a measurement built on generations of insight and breakthrough. </p>
<h2>Predictions without observation</h2>
<p>In the early 1900s, considerable progress occurred after Albert Einstein developed his theories of relativity. These enduring equations link space and time, and dictate the motion of matter which in turn dictates the gravitational fields and waves within spacetime.</p>
<p>Soon after, in 1916, astronomers Karl Schwarzschild and Johannes Droste independently realised that Einstein’s equations gave rise to solutions containing a “mathematical singularity”, an indivisible point of zero volume and infinite mass. </p>
<p>Studying the evolution of stars in the 1920s and 1930s, nuclear physicists reached the seemingly unavoidable conclusion that if massive enough, certain stars would end their lives in a catastrophic gravitational collapse resulting in a singularity and the creation of a “frozen star”.</p>
<p>This term reflected the bizarre relative nature of time in Einstein’s theory. At the event horizon, the infamous boundary of no return surrounding such a collapsed star, time will appear to freeze for an external observer. </p>
<p>While advances in the field of quantum mechanics replaced the notion of a singularity with an equally bewildering but finite quantum dot, the actual surface, and interior, of black holes remains an active area of research today.<br>
While our galaxy may contain millions of John Michell’s stellar-mass black holes — of which we know the whereabouts of a dozen or so — their event horizons are too small to observe. </p>
<p>For example, if our Sun were to collapse down to a black hole, the radius of its event horizon would be just 3km. But the collision of stellar-mass black holes in other galaxies was <a href="http://adsabs.harvard.edu/abs/2016PhRvL.116f1102A" title="Observation of Gravitational Waves from a Binary Black Hole Merger">famously detected</a> using gravitational waves. </p>
<h2>Looking for something supermassive</h2>
<p>The EHT’s targets are therefore related to the supermassive black holes located at the centres of galaxies. The term black hole actually only came into use in the mid- to late 1960s when astronomers began to suspect that truly massive “dark stars” powered the highly active nuclei of certain galaxies. </p>
<p>Numerous theories abound for the formation of these particularly massive black holes. Despite the name, black holes are objects, rather than holes in the fabric of spacetime. </p>
<p>In 1972, <a href="http://adsabs.harvard.edu/full/1972AJ.....77..292S" title="The Distribution of Mass in the Galactic Nucleus">Robert Sanders and Thomas Lowinger</a> calculated that a dense mass equal to about one million solar masses resides at the centre of our galaxy. </p>
<p>By 1978, <a href="http://adsabs.harvard.edu/doi/10.1086/156077" title="Dynamical evidence for a central mass concentration in the galaxy M87">Wallace Sargent and colleagues had determined</a> that a dense mass five billion times the mass of our Sun lies at the centre of the nearby galaxy M87. </p>
<p>But these masses, slightly revised since then, might have simply been a dense swarm of planets and dead stars. </p>
<p>In 1995, the existence of black holes was confirmed observationally by <a href="http://adsabs.harvard.edu/abs/1995Natur.373..127M" title="Evidence for a black hole from high rotation velocities in a sub-parsec region of NGC4258">Makoto Miyoshi and colleagues</a>. Using radio interferometry, they detected a mass at the centre of the galaxy M106, within a volume so small that it could only be, or soon would become, a black hole.</p>
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<a href="https://theconversation.com/first-black-hole-photo-confirms-einsteins-theory-of-relativity-115167">First black hole photo confirms Einstein's theory of relativity</a>
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<p>Today, around 130 such supermassive black holes at the centres of nearby galaxies have had their masses directly measured from the orbital velocities and distances of stars and gas circling the black holes, but not yet on a death spiral into the central gravitational compactor.</p>
<p>Despite the increased sample, our Milky Way and M87 still have the largest event horizons as seen from Earth, which is why the international team pursued these two targets.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1115964692802019328"}"></div></p>
<p>The shadowy silhouette of the black hole in M87 is indeed an astonishing scientific image. While black holes can apparently stop time, it should be acknowledged that the predictive power of science, when coupled with human imagination, ingenuity, and determination, is also a remarkable force of nature.</p><img src="https://counter.theconversation.com/content/115064/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Professor Alister Graham is an Associate Investigator at the Australian Research Council’s Centre of Excellence for Gravitational Wave Discovery, known as OzGrav, headquartered at Swinburne University of Technology in Melbourne. </span></em></p>Astronomers say they have “seen what we thought was unseeable” in releasing the first image of a supermassive black hole. So how did we get to this historic observation?Alister Graham, Professor of Astronomy, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1151672019-04-10T16:05:17Z2019-04-10T16:05:17ZFirst black hole photo confirms Einstein’s theory of relativity<figure><img src="https://images.theconversation.com/files/268630/original/file-20190410-2905-t29uaz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Finally dragged out of the shadows.</span> <span class="attribution"><a class="source" href="https://eventhorizontelescope.org">Event Horizon Telescope Collaboration / </a></span></figcaption></figure><p>Black holes are long-time superstars of science fiction. But their Hollywood fame is a little strange given that no-one has ever actually seen one – at least, until now. If you needed to see to believe, then thank the <a href="https://eventhorizontelescope.org">Event Horizon Telescope</a> (EHT), which has just produced the first ever direct image of a black hole. This amazing feat required global collaboration to turn the Earth into one giant telescope and image an object thousands of trillions of kilometres away.</p>
<p>As stunning and ground-breaking as it is, the EHT project is not just about taking on a challenge. It’s an unprecedented test of whether Einstein’s <a href="https://theconversation.com/explainer-einsteins-theory-of-general-relativity-3481">ideas</a> about the very nature of space and time hold up in extreme circumstances, and looks closer than ever before at the role of black holes in the universe. </p>
<p>To cut a long story short: Einstein was right.</p>
<h2>Capturing the uncapturable</h2>
<p>A black hole is a region of space whose mass is so large and dense that not even light can escape its gravitational attraction. Against the black backdrop of the inky beyond, capturing one is a near impossible task. But thanks to Stephen Hawking’s groundbreaking work, we know that the colossal masses <a href="https://theconversation.com/black-holes-arent-totally-black-and-other-insights-from-stephen-hawkings-groundbreaking-work-93458">are not just black abysses</a>. Not only are they able to emit huge jets of plasma, but their immense gravity pulls in streams of matter into its core.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1116287990928687105"}"></div></p>
<p>When matter approaches a black hole’s event horizon – the point at which not even light can escape – it forms an orbiting disk. Matter in this disk will convert some of its energy to friction as it rubs against other particles of matter. This warms up the disk, just as we warm our hands on a cold day by rubbing them together. The closer the matter, the greater the friction. Matter closer to the event horizon glows brilliantly bright with the heat of hundreds of Suns. It is this light that the EHT detected, along with the “silhouette” of the black hole. </p>
<p>Producing the image and analysing such data is an amazingly hard task. As an astronomer who studies <a href="https://ui.adsabs.harvard.edu/abs/2018MNRAS.475.4223G/abstract">black holes in far away galaxies</a>, I cannot usually even image a single star in those galaxies clearly, let alone see the black hole at their centres.</p>
<p>The EHT team decided to target two of the closest supermassive black holes to us – both in the large elliptical shaped galaxy, M87, and in Sagittarius A*, at the centre of our Milky Way. </p>
<p>To give a sense of how hard this task is, while the Milky Way’s black hole has a mass of 4.1 million Suns and a diameter of 60 million kilometres, it is 250,614,750,218,665,392 kilometres away from Earth – thats the equivalent of travelling from London to New York 45 trillion times. As <a href="https://www.youtube.com/watch?v=hMsNd1W_lmE">noted by the EHT team</a>, it is like being in New York and trying to count the dimples on a golf ball in Los Angeles, or imaging an orange on the moon. </p>
<p>To photograph something so impossibly far away, the team needed a telescope as big as the Earth itself. In the absence of such a gargantuan machine, the EHT team connected together telescopes from around the planet, and combined their data. To capture an accurate image at such a distance, the telescopes needed to be stable, and their readings completely synchronised.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/hMsNd1W_lmE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How the researchers captured the first image of a black hole.</span></figcaption>
</figure>
<p>To accomplish this challenging feat, the team used atomic clocks so accurate that they lose just one second per hundred million years. The 5,000 terabytes of data collected was so large that it had to be stored on hundreds of hard drives and physically delivered to a supercomputer, which corrected the time differences in the data and produced the image above.</p>
<h2>General Relativity vindicated</h2>
<p>With a sense of excitement, I watched the live stream showing the image of the black hole from the centre of M87 for the first time.</p>
<p>The most important initial take-home is that Einstein was right. <a href="https://theconversation.com/gravitational-waves-discovered-top-scientists-respond-53956">Again</a>. His general theory of relativity has passed two serious tests from the universe’s most extreme conditions in the last few years. Here, Einstein’s theory predicted the observations from M87 with unerring accuracy, and is seemingly the correct description of the nature of space, time, and gravity.</p>
<p>The measurements of the speeds of matter around the centre of the black hole are consistent with being near the speed of light. From the image, the EHT scientists determined that the M87 black hole is 6.5 billion times the mass of the Sun and 40 billion km across – that’s larger than Neptune’s 200-year orbit of the sun. </p>
<p>The Milky Way’s black hole was too challenging to image accurately this time round due to rapid variability in light output. Hopefully, more telescopes will be added to the EHT’s array soon, to get ever clearer images of these fascinating objects. I have no doubt that in the near future we will be able to gaze upon the dark heart of our very own galaxy.</p>
<p><em>This piece has been updated to include a picture of Katie Bouman, a computer scientist who developed the algorithm that made the black hole photo possible.</em></p><img src="https://counter.theconversation.com/content/115167/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kevin Pimbblet receives funding from STFC. </span></em></p>Scientists turned Earth into one giant telescope to capture the uncapturable.Kevin Pimbblet, Senior Lecturer in Physics, University of HullLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1081812018-12-18T13:44:46Z2018-12-18T13:44:46ZHow we’re probing the secrets of a giant black hole at our galaxy’s centre<figure><img src="https://images.theconversation.com/files/248668/original/file-20181204-126674-11iq133.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The region around the supermassive black hole at the centre of the Milky Way, imaged with South Africa's MeerKAT telescope.</span> <span class="attribution"><span class="source">South African Radio Astronomy Observatory (SARAO)</span></span></figcaption></figure><p>Supermassive black holes are giant black holes found at the centre of almost every galaxy. Astronomers recently made the clearest image yet of the supermassive black hole at the heart of our own galaxy using the new <a href="http://www.ska.ac.za/science-engineering/meerkat/">MeerKAT radio telescope</a> in South Africa, revealing the features surrounding it in exquisite detail. </p>
<p>The giant black hole in our galaxy is passive, sitting by idly as galactic processes go on around it. In other galaxies, however, black holes are active: gas and dust are falling into their central supermassive black hole. This causes vast amounts of energy to be released into space and produces violent outflows of material which can travel for many thousands of kilometres through space.</p>
<p>The new MeerKAT telescope will help us unlock the secrets of these massive beasts, making this an exciting time for astronomers all over the world.</p>
<h2>Huge and mysterious</h2>
<p>A black hole is an object with such a strong gravitational pull that nothing, not even light, can escape from. This occurs because they have a large mass crammed into a very small area, creating an extremely dense object. </p>
<p>The existence of black holes <a href="https://www.reuters.com/article/us-space-milky-way/scientists-confirm-einsteins-supermassive-black-hole-theory-idUSKBN1KG28G">was predicted</a> from mathematical theories by physicist Albert Einstein, astronomer and physicist Karl Schwarzschild and others several decades before they were first discovered. </p>
<p>Most black holes are about 10 times heavier than our sun. They are formed when the core of a large star collapses at the end of its life, leaving behind an extremely dense object. There are millions of these small black holes in our galaxy alone. </p>
<p>“Supermassive” black holes are particularly heavy black holes which are found at the centre of almost every galaxy. These black holes are millions to billions of times more massive than our sun – which is where they get their name from – and exactly how they form is still a mystery.</p>
<p>Astronomers first realised there is a black hole at the centre of our own galaxy by <a href="https://www.eso.org/public/videos/eso0226a/">looking at the motion of the stars very close to the centre</a> and realising that they must be orbiting something very heavy that we can’t see. The only thing that could be this massive and fit into such a small piece of space is a very heavy black hole.</p>
<h2>In the Milky Way</h2>
<p>We’ve recently made the best image yet of the area around the supermassive black hole at the heart of the Milky Way using the <a href="https://theconversation.com/a-big-moment-for-africa-why-the-meerkat-and-astronomy-matter-99714">brand new</a> MeerKAT telescope. MeerKAT consists of 64 dishes, each 13.5m across, situated in South Africa’s Northern Cape province. It will eventually be incorporated into the Square Kilometre Array (SKA) – an ambitious project to build the world’s largest radio telescope. Launched in July, MeerKAT is already the largest and most sensitive radio telescope in the southern hemisphere.</p>
<p>With this powerful new machine, we’ve been able to produce the clearest image yet of the centre of our galaxy – you can see it at the top of this story. This extraordinary image provides a wealth of new information about the heart of the Milky Way. The supermassive black hole itself is in the middle of the bright patch at the centre of the image; it’s surrounded by plasma which is glowing brightly.</p>
<p>The bright, spark-like, filamentary structures in the image have never been seen in such detail before and their exact origin remains a mystery. They are seen close to the supermassive black hole but nowhere else in the galaxy. </p>
<p>This stunning image also provides a clearer view of features that have previously been observed in the Milky Way – among them the bubble-like objects on the left-hand side of the image. These are shock waves caused when a star explodes in a supernova at the end of its life. As part of this processes the core of the star collapses and may create a small black hole.</p>
<h2>Meanwhile, elsewhere</h2>
<p>Our galaxy isn’t the only one with a supermassive black hole at its centre. In fact astronomers think that almost all galaxies contain a similar giant black hole. </p>
<p>In nine out of 10 galaxies, including our own, the supermassive black hole is passive: it minds its own business while the galaxy continues as normal around it. </p>
<p>Other supermassive black holes are feeding on nearby gas and dust, causing a colossal amount of energy to be released. In many cases, this causes the region around the central black hole to glow so brightly that it outshines the total light from all of the stars in the galaxy. </p>
<p>Some of these black holes also produce <a href="https://theconversation.com/radio-galaxies-the-mysterious-secretive-beasts-of-the-universe-64381">powerful jets of lightning-fast particles</a>, which travel for many thousands of kilometres through space. I am using the MeerKAT telescope to <a href="https://theconversation.com/telescopes-in-southern-africa-will-peel-back-the-universes-secrets-from-2018-88668">study these giant jets</a>, and the role they play in the life cycle of galaxies, like our Milky Way. It’s early days for my research, but I soon hope to provide some valuable answers to our many questions about these jets.</p>
<p>It’s early days for MeerKAT, too: it has just started science operations. That means the best is yet to come. More data and more images will help us to understand our galaxy and others far better than we ever have before.</p><img src="https://counter.theconversation.com/content/108181/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Imogen Whittam works for the University of the Western Cape. She receives funding from the South African Radio Astronomy Observatory. </span></em></p>A black hole is an object with such a strong gravitational pull that nothing, not even light, can escape from it.Imogen Whittam, Post-doctoral researcher in Astrophysics, University of the Western CapeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1069522018-11-15T19:11:38Z2018-11-15T19:11:38ZHere’s how the ‘brightest’ object in the universe formed<figure><img src="https://images.theconversation.com/files/245735/original/file-20181115-194513-gdvgoj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression of quasar W2246-0526.</span> <span class="attribution"><span class="source"> NRAO/AUI/NSF; Dana Berry / SkyWorks; ALMA (ESO/NAOJ/NRAO)</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Active galaxies are some of the most luminous and impressive objects in the sky. They tend to be massive, distant and emit extraordinary amounts of energy as material falls into the supermassive black hole that lurks at their centre. Astronomers have recently discovered that some of them are also hidden from plain view by huge amounts of gas and smoke-like dust. But it is unclear how these rare objects form and feed.</p>
<p>Now our team of astronomers has worked out more about the origin of the most luminous galaxy found in the universe: a <a href="https://www.eso.org/public/news/eso1602/">“quasar” called W2246</a>. Our findings, <a href="http://science.sciencemag.org/lookup/doi/10.1126/science.aap7605">published in Science</a>, show clear signs of W2246 forming by several galaxies merging. </p>
<p>W2246 was first discovered in the all-sky infrared survey made by the <a href="https://www.nasa.gov/mission_pages/WISE/main/index.html">WISE spacecraft</a> in 2010. But we don’t see it as it looks today. When we look out into the universe we detect light that has taken some appreciable time to get to us. This galaxy is so far away that we see it as it was when the universe was only about 8% of its present age. </p>
<p>The object is extremely bright – about 10,000 times more luminous than our galaxy, the Milky Way. Previous work using a range of cutting-edge telescopes – including <a href="https://www.almaobservatory.org/en/home/">the Atacama Large Millimetre Array (ALMA)</a>, and the Hubble and Herschel Space Telescopes – confirmed in 2016 that W2246 is the current holder of the record for the <a href="https://arxiv.org/abs/1511.04079">most luminous galaxy in the universe</a>.</p>
<p>The bulk of the power from W2246 emanates from a relatively compact region in its centre, several times smaller than the Milky Way. The images also show that this region contains a remarkable cloud of hot, uniform, high-pressure gas, plausibly starting to expand out as a bubble in all directions. </p>
<h2>New observations</h2>
<p>The latest observations were carried out by my colleague <a href="http://astronomia.udp.cl/tanio-diaz-santos/">Tanio Diaz Santos</a> in Chile, and 11 other astronomers, using the ALMA and <a href="https://science.nrao.edu/facilities/vla">Jansky Very Large Array (JCLA)</a> telescopes, at excellent sites in Chile and New Mexico respectively. The work has revealed the smog of gas and dust contained within W2246 in unprecedented detail. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/245566/original/file-20181114-194488-1vhyd9x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/245566/original/file-20181114-194488-1vhyd9x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=594&fit=crop&dpr=1 600w, https://images.theconversation.com/files/245566/original/file-20181114-194488-1vhyd9x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=594&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/245566/original/file-20181114-194488-1vhyd9x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=594&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/245566/original/file-20181114-194488-1vhyd9x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=747&fit=crop&dpr=1 754w, https://images.theconversation.com/files/245566/original/file-20181114-194488-1vhyd9x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=747&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/245566/original/file-20181114-194488-1vhyd9x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=747&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">ALMA image of W2246-0526 and its companions feeding it through trans-galactic streamers.</span>
<span class="attribution"><span class="source">T. Diaz-Santos et al.; N. Lira; ALMA (ESO/NAOJ/NRAO)</span></span>
</figcaption>
</figure>
<p>The fact that W2246 could be so bright without feeding on nearby galaxies has long been a mystery to astronomers – potentially challenging our theories about galaxy formation. But our new results reveal that there are indeed a number of nearby companion galaxies that are in the process of being gobbled up by this object. This is evidenced by connecting dust bridges of carbon-rich solid material, similar to diesel soot. These trace the routes along which matter from the companion galaxies is being sucked in towards the supermassive black hole.</p>
<p>The presence of dust is important as it is made of elements that are only produced by nuclear reactions deep inside massive stars, and are then spread around the galaxy when these stars explode as supernovae. This indicates that the gas seen around W2246 has been cycled inside stars in the past – probably in the surrounding galaxies – prior to the start of the galaxy’s current dramatic burst of activity. The new images therefore provide insight not only into the activity in the galaxy as we see it today, but also into its history at even earlier times.</p>
<p>To be visible to ALMA, the bridging dust must be actively heated. This could be done by young stars that also occupy the bridges, or by the radiation from the hugely bright core of W2246. The conditions in the gas within the bridges suggest that even if W2246 is the primary heat source, the gas in the bridges can still collapse under its own gravity to form new stars in dense clouds, which would allow it to be gobbled up by the central black hole to fuel W2246.</p>
<p>From the relative speed and separation of the companion galaxies, it is possible to work out how much mass they contain. We can also estimated that the duration of the current interaction is about 200m years. Together, we used this to determine the rate at which gas must be fed into the black hole, uncovering that it is indeed sufficient to produce the dramatic energy output we see from the object.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/245765/original/file-20181115-194491-bzmrju.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/245765/original/file-20181115-194491-bzmrju.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/245765/original/file-20181115-194491-bzmrju.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/245765/original/file-20181115-194491-bzmrju.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/245765/original/file-20181115-194491-bzmrju.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/245765/original/file-20181115-194491-bzmrju.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/245765/original/file-20181115-194491-bzmrju.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">ALMA antennas.</span>
<span class="attribution"><span class="source">Iztok Bončina/ESO</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>However, the details of what happens within the bright compact core of the galaxy as this material rains in, and enters the the black hole (that then heats and drives away material) can’t be seen. Observations on finer scales will be needed to investigate what happens deep in the heart of W2246. </p>
<h2>Out with a whimper?</h2>
<p>Luckily, further observations using ALMA and the forthcoming <a href="https://theconversation.com/how-hubbles-successor-will-give-us-a-glimpse-into-the-very-first-galaxies-45970">James Webb Space Telescope (JWST)</a>, scheduled for launch in 2021, will be able to reveal exactly how the gas and dust travels within and is distributed around the galaxies, gets converted into stars and is consumed by the black hole.</p>
<p>Not only will these observations give insight into this most extreme galaxy, it could also help us understand the processes that build more ordinary galaxies, and the conditions required to ignite all galaxies’ most luminous phases. </p>
<p>It’s been great watching W2246. In about 100m years, it will definitely have finished its meal of neighbouring galaxies. It will then lose its sparkle, and another object will take the crown of being the brightest galaxy in the universe. Nothing is forever.</p><img src="https://counter.theconversation.com/content/106952/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Blain receives or has received funding from The Royal Society, STFC, NSF and NASA </span></em></p>A number of surrounding galaxies are slowly being devoured by the most luminous object in the sky.Andrew Blain, Professor of Observational Astronomy, University of LeicesterLicensed as Creative Commons – attribution, no derivatives.