tag:theconversation.com,2011:/nz/topics/neutron-stars-1325/articlesNeutron stars – The Conversation2024-03-27T23:55:16Ztag:theconversation.com,2011:article/2267292024-03-27T23:55:16Z2024-03-27T23:55:16ZA cosmic ‘speed camera’ just revealed the staggering speed of neutron star jets in a world first<figure><img src="https://images.theconversation.com/files/584904/original/file-20240327-26-ntaiw6.jpg?ixlib=rb-1.1.0&rect=1283%2C180%2C5431%2C3798&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Nuclear explosions on a neutron star feed its jets.
</span> <span class="attribution"><span class="source">Danielle Futselaar and Nathalie Degenaar, Anton Pannekoek Institute, University of Amsterdam</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>How fast can a neutron star drive powerful jets into space? The answer, it turns out, is about one-third the speed of light, as our team has just revealed in a <a href="https://www.nature.com/articles/s41586-024-07133-5">new study</a> published in Nature.</p>
<p>Energetic cosmic beams known as <a href="https://www.britannica.com/science/radio-jet">jets</a> are seen throughout our universe. They are launched when material – mainly dust and gas – falls in towards any dense central object, such as a neutron star (an extremely dense remnant of a once-massive star) or a <a href="https://science.nasa.gov/universe/black-holes/">black hole</a>. </p>
<p>The jets carry away some of the gravitational energy released by the infalling gas, recycling it back into the surroundings on far larger scales.</p>
<p>The most powerful jets in the universe come from the biggest black holes at the centres of galaxies. The energy output of these jets can affect the evolution of an entire galaxy, or even a galaxy cluster. This makes jets a critical, yet intriguing, component of our universe.</p>
<p>Although jets are common, we still don’t fully understand how they are launched. Measuring the jets from a neutron star has now given us valuable information.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-brightest-object-in-the-universe-is-a-black-hole-that-eats-a-star-a-day-222612">The brightest object in the universe is a black hole that eats a star a day</a>
</strong>
</em>
</p>
<hr>
<h2>Jets from stellar corpses</h2>
<p>Jets from black holes tend to be bright, and have been well studied. However, the jets from neutron stars are typically much fainter, and much less is known about them.</p>
<p>This presents a problem, since we can learn a lot by comparing the jets launched by different celestial objects. <a href="https://imagine.gsfc.nasa.gov/science/objects/neutron_stars1.html">Neutron stars</a> are extremely dense stellar corpses – cosmic cinders the size of a city, yet containing the mass of a star. We can think of them as enormous atomic nuclei, each about 20 kilometres across.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/M8DmwNvtfxk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>In contrast to black holes, neutron stars have both a solid surface and a magnetic field, and gas falling onto them releases less gravitational energy. All of these properties will have an effect on how their jets are launched, making studies of neutron star jets particularly valuable.</p>
<p>One key clue to how jets are launched comes from their speeds. If we can determine how jet speeds vary with the mass or spin of the neutron star, that would provide a powerful test of theoretical predictions. But it is extremely challenging to measure jet speeds accurately enough for such a test.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/unexpected-find-from-a-neutron-star-forces-a-rethink-on-radio-jets-103843">Unexpected find from a neutron star forces a rethink on radio jets</a>
</strong>
</em>
</p>
<hr>
<h2>A cosmic speed camera</h2>
<p>When we measure speeds on Earth, we time an object between two points. This could be a 100-metre sprinter running down the track, or a point-to-point speed camera tracking a car.</p>
<p>Our team, led by Thomas Russell from the <a href="http://www.inaf.it/en">Italian National Institute of Astrophysics</a> in Palermo, conducted a new experiment to do this for neutron star jets.</p>
<p>What has made this measurement so difficult in the past is that jets are steady flows. This means there is no single starting point for our timer. But we were able to identify a short-lived signal at X-ray wavelengths that we could use as our “starting gun”.</p>
<p>Being so dense, neutron stars can “steal” matter from a nearby orbiting companion star. While some of that gas is launched outwards as jets, most of it ends up falling onto the neutron star. As the material piles up, it gets hotter and denser.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/DU43sUjGeL4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>When enough material has built up, it triggers a thermonuclear explosion. A runaway nuclear fusion reaction occurs and rapidly spreads to engulf the entire star. The fusion lasts for a few seconds to minutes, causing a short-lived <a href="https://www.nasa.gov/universe/nasas-nicer-catches-record-setting-x-ray-burst/">burst of X-rays</a>.</p>
<h2>One step closer to solving a mystery</h2>
<p>We thought this thermonuclear explosion would disrupt the neutron star’s jets. So, we used CSIRO’s <a href="https://www.csiro.au/en/about/facilities-collections/atnf/australia-telescope-compact-array">Australia Telescope Compact Array</a> to stare at the jets for three days at radio wavelengths to try and catch the disruption. At the same time, we used the European Space Agency’s <a href="https://www.esa.int/Science_Exploration/Space_Science/Integral_overview">Integral</a> telescope to look at the X-rays from the system.</p>
<p>To our surprise, we found the jets got brighter after every pulse of X-rays. Instead of disrupting the jets, the thermonuclear explosions seemed to power them up. And this pattern was repeated ten times in one neutron star system, and then again in a second system.</p>
<p>We can explain this surprising result if the X-ray pulse causes gas swirling around the neutron star to fall inwards more quickly. This, in turn, provides more energy and material to divert into the jets.</p>
<p>Most importantly, however, we can use the X-ray burst to indicate the launch time of the jets. We timed how long they took to move outwards to where they became visible at two different radio wavelengths. These start and finish points provided us with our cosmic speed camera.</p>
<p>Interestingly, the jet speed we measured was close to the “escape speed” from a neutron star. On Earth, this escape speed is <a href="https://www.britannica.com/science/escape-velocity">11.2 kilometres per second</a> – what rockets need to achieve to break free of Earth’s gravity. For a neutron star, that value is around half the speed of light.</p>
<p>Our work has introduced a new technique for measuring neutron star jet speeds. Our next steps will be to see how the jet speed changes for neutron stars with different masses and rotation rates. That will allow us to directly test theoretical models, taking us one step closer to figuring out how such powerful cosmic jets are launched.</p><img src="https://counter.theconversation.com/content/226729/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Miller-Jones receives funding from the Australian Research Council and the Western Australian State Government.</span></em></p>Powerful jets are launched from the most massive objects in our universe, but we don’t fully understand how. This measurement gets us a step closer to solving the mystery.James Miller-Jones, Professor, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2211902024-01-18T19:03:30Z2024-01-18T19:03:30ZBlack hole, neutron star or something new? We discovered an object that defies explanation<figure><img src="https://images.theconversation.com/files/569626/original/file-20240116-25-e4m99b.jpg?ixlib=rb-1.1.0&rect=0%2C19%2C2657%2C1463&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of the the NGC 1851E binary system, looking over the shoulder of the dark mystery companion star</span> <span class="attribution"><span class="source">MPIfR; Daniëlle Futselaar (artsource.nl)</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Sometimes astronomers come across objects in the sky that we can’t easily explain. In our new research, published in Science, <a href="https://www.science.org/doi/10.1126/science.adg3005">we report such a discovery</a>, which is likely to spark discussion and speculation.</p>
<p>Neutron stars are some of the densest objects in the universe. As compact as an atomic nucleus, yet as large as a city, they push the limits of our understanding of extreme matter. The heavier a neutron star is, the more likely it is to eventually collapse to become something even denser: a black hole. </p>
<p>These astrophysical objects are so dense, and their gravitational pulls so strong, that their cores – whatever they may be – are permanently shrouded from the universe by event horizons: surfaces of perfect darkness from which light cannot escape.</p>
<p>If we are to ever understand the physics at the tipping point between neutron stars and black holes, we must find objects at this boundary. In particular, we must find objects for which we can make precise measurements over long periods of time. And that’s precisely what we’ve found – an object that is neither obviously a neutron star nor a black hole.</p>
<p>It was when looking deep in the star cluster <a href="https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-caldwell-catalog/caldwell-73/">NGC 1851</a> that we spotted what appears to be a pair of stars offering a new view into the extremes of matter in the universe. The system is composed of a <a href="https://public.nrao.edu/gallery/how-to-make-a-millisecond-pulsar/">millisecond pulsar</a>, a type of rapidly spinning neutron star that sweeps beams of radio light across the cosmos as it spins, and a massive, hidden object of unknown nature. </p>
<p>The massive object is dark, meaning it is invisible at all frequencies of light – from the radio to the optical, x-ray and gamma-ray bands. In other circumstances this would make it impossible to study, but it is here that the millisecond pulsar comes to our aid.</p>
<p>Millisecond pulsars are akin to cosmic atomic clocks. Their spins are incredibly stable and can be precisely measured by detecting the regular radio pulse they create. Although intrinsically stable, the observed spin changes when the pulsar is in motion or when its signal is affected by a strong gravitational field. By observing these changes we can measure the properties of bodies in orbits with pulsars.</p>
<p>Our international team of astronomers has been using the <a href="https://www.sarao.ac.za/gallery/meerkat/">MeerKAT radio telescope</a> in South Africa to conduct such observations of the system, referred to as NGC 1851E. </p>
<p>These allowed us to precisely detail the orbits of the two objects, showing that their point of closest approach changes with time. Such changes are described by <a href="https://theconversation.com/how-einsteins-general-theory-of-relativity-killed-off-common-sense-physics-50042">Einstein’s theory of relativity</a> and the speed of a change tells us about the combined mass of the bodies in the system. </p>
<p>Our observations revealed that the NGC 1851E system weighs almost four times as much as our Sun, and that the dark companion was, like the pulsar, a compact object – much denser than a normal star. The most massive neutron stars weigh in at around two solar masses, so if this were a double neutron star system (systems that are well known and studied) then it would have to contain two of the heaviest neutron stars ever found.</p>
<p>To uncover the nature of the companion, we would need to understand how the mass in the system was distributed between the stars. Again using Einstein’s general relativity, we could model the system in detail, finding the mass of the companion to lie between 2.09 and 2.71 times the mass of the Sun.</p>
<p>The companion’s mass falls within the <a href="https://uwm.edu/news/exploring-the-mysterious-gap-between-black-holes-and-neutron-stars/#:%7E:text=For%20decades%20astronomers%20have%20been,is%20about%205%20solar%20masses.">“black hole mass gap”</a> that lies between heaviest possible neutron stars, thought to be around 2.2 solar masses, and the lightest black holes that can be formed from stellar collapse, around 5 solar masses. The nature and formation of objects in this gap is an outstanding question in astrophysics.</p>
<h2>Possible candidates</h2>
<p>So what exactly have we found then?</p>
<p>An enticing possibility is that we have uncovered a pulsar in orbit around the remains of a merger (collision) of two neutron stars. Such an unusual configuration is made possible by the dense packing of stars in NGC 1851. </p>
<p>In this crowded stellar dance floor, stars will twirl around one another, swapping partners in an endless waltz. If two neutron stars happen to be thrown too close together, their dance will come to a cataclysmic end. </p>
<p>The black hole created by their collision, which can be much lighter than those created from collapsing stars, is then free to wander the cluster until it finds another pair of dancers in the waltz and, rather rudely, insert itself – kicking out the lighter partner in the process. It is this mechanism of collisions and exchanges that could give rise to the system we observe today.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/sm47qF0n6MI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Simulation of the three-body interaction that is thought to have produced the NGC 1851E system.</span></figcaption>
</figure>
<p>We are not done with this system yet. Work is already ongoing to conclusively identify the true nature of the companion and reveal whether we have discovered the lightest black hole or the most massive neutron star – or perhaps neither. </p>
<p>At the boundary between neutron stars and black holes there is always the possibility that some new, as yet unknown, astrophysical object might exist. </p>
<p>Much speculation will be sure to follow this discovery, but what is already clear is that this system holds immense promise when it comes to understanding what really happens to matter in the most extreme environments in the universe.</p><img src="https://counter.theconversation.com/content/221190/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Benjamin Stappers receives funding from UKRI.</span></em></p><p class="fine-print"><em><span>Arunima Dutta and Ewan D. Barr 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>It’s too heavy to be a neutron star and too light to be a black hole. So what is it?Ewan D. Barr, Project scientist for the Transients and Pulsars with MeerKAT (TRAPUM) collaboration, Max Planck Institute for Radio AstronomyArunima Dutta, PhD Candidate at the Research Department Fundamental Physics in Radio Astronomy, Max Planck Institute for Radio AstronomyBenjamin Stappers, Professor of Astrophysics, University of ManchesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2043392023-05-22T12:27:17Z2023-05-22T12:27:17ZGravitational wave detector LIGO is back online after 3 years of upgrades – how the world’s most sensitive yardstick reveals secrets of the universe<figure><img src="https://images.theconversation.com/files/527292/original/file-20230519-29-jhi1qv.jpg?ixlib=rb-1.1.0&rect=335%2C178%2C6276%2C2651&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When two massive objects – like black holes or neutron stars – merge, they warp space and time. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/gravitational-waves-illustration-royalty-free-illustration/685026451?phrase=gravitational+waves&adppopup=true">Mark Garlick/Science Photo Library via Getty Images</a></span></figcaption></figure><p>After a three-year hiatus, scientists in the U.S. have just turned on detectors capable of <a href="https://observing.docs.ligo.org/plan/">measuring gravitational waves</a> – tiny ripples in space itself that travel through the universe. </p>
<p>Unlike light waves, gravitational waves are nearly <a href="https://www.ligo.caltech.edu/page/why-detect-gw">unimpeded by the galaxies, stars, gas and dust</a> that fill the universe. This means that by measuring gravitational waves, <a href="https://scholar.google.com/citations?user=33fO9GoAAAAJ&hl=en&oi=sra">astrophysicists like me</a> can peek directly into the heart of some of these most spectacular phenomena in the universe. </p>
<p>Since 2020, the Laser Interferometric Gravitational-Wave Observatory – commonly known as <a href="https://www.ligo.caltech.edu">LIGO</a> – has been sitting dormant while it underwent some exciting upgrades. These improvements will <a href="https://doi.org/10.1103/PhysRevX.13.011048">significantly boost the sensitivity</a> of LIGO and should allow the facility to observe more-distant objects that produce smaller ripples in <a href="https://theconversation.com/why-does-gravity-pull-us-down-and-not-up-162141">spacetime</a>.</p>
<p>By detecting more events that create gravitational waves, there will be more opportunities for astronomers to also observe the light produced by those same events. Seeing an event <a href="https://theconversation.com/ligo-announcement-vaults-astronomy-out-of-its-silent-movie-era-into-the-talkies-85727">through multiple channels of information</a>, an approach called <a href="https://doi.org/10.1038/s42254-019-0101-z">multi-messenger astronomy</a>, provides astronomers <a href="https://doi.org/10.3847/2041-8213/aa91c9">rare and coveted opportunities</a> to learn about physics far beyond the realm of any laboratory testing.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the Sun and Earth warping space." src="https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=440&fit=crop&dpr=1 754w, https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=440&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/527293/original/file-20230519-25-cqwibh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=440&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">According to Einstein’s theory of general relativity, massive objects warp space around them.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/gravity-and-general-theory-of-relativity-concept-royalty-free-image/923504630?phrase=gravity+general+relativity&adppopup=true">vchal/iStock via Getty Images</a></span>
</figcaption>
</figure>
<h2>Ripples in spacetime</h2>
<p>According to <a href="https://theconversation.com/why-does-gravity-pull-us-down-and-not-up-162141">Einstein’s theory of general relativity</a>, mass and energy warp the shape of space and time. The bending of spacetime determines how objects move in relation to one another – what people experience as gravity. </p>
<p>Gravitational waves are created when massive objects like black holes or neutron stars merge with one another, producing sudden, large changes in space. The process of space warping and flexing sends ripples across the universe like a <a href="https://www.ligo.caltech.edu/page/what-are-gw">wave across a still pond</a>. These waves travel out in all directions from a disturbance, minutely bending space as they do so and ever so slightly changing the distance between objects in their way. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/_C5Bl_hE8fM?wmode=transparent&start=17" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">When two massive objects – like a black hole or a neutron star – get close together, they rapidly spin around each other and produce gravitational waves. The sound in this NASA visualization represents the frequency of the gravitational waves.</span></figcaption>
</figure>
<p>Even though the astronomical events that produce gravitational waves involve some of the most massive objects in the universe, the stretching and contracting of space is infinitesimally small. A strong gravitational wave passing through the Milky Way may only change the diameter of the entire galaxy by three feet (one meter).</p>
<h2>The first gravitational wave observations</h2>
<p>Though first predicted by Einstein in 1916, scientists of that era had little hope of measuring the tiny changes in distance postulated by the theory of gravitational waves.</p>
<p>Around the year 2000, scientists at Caltech, the Massachusetts Institute of Technology and other universities around the world finished constructing what is essentially the most precise ruler ever built – the <a href="https://doi.org/10.1088/0034-4885/72/7/076901">LIGO observatory</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An L-shaped facility with two long arms extending out from a central building." src="https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/527294/original/file-20230519-21-zdmud0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The LIGO detector in Hanford, Wash., uses lasers to measure the minuscule stretching of space caused by a gravitational wave.</span>
<span class="attribution"><a class="source" href="https://www.ligo.org/multimedia/gallery/lho-images/Aerial5.jpg">LIGO Laboratory</a></span>
</figcaption>
</figure>
<p><a href="https://www.ligo.caltech.edu/page/what-is-ligo">LIGO is comprised of two separate observatories</a>, with one located in Hanford, Washington, and the other in Livingston, Louisiana. Each observatory is shaped like a giant L with two, 2.5-mile-long (four-kilometer-long) arms extending out from the center of the facility at 90 degrees to each other.</p>
<p>To measure gravitational waves, researchers shine a laser from the center of the facility to the base of the L. There, the laser is split so that a beam travels down each arm, reflects off a mirror and returns to the base. If a gravitational wave passes through the arms while the laser is shining, the two beams will return to the center at ever so slightly different times. By measuring this difference, physicists can discern that a gravitational wave passed through the facility.</p>
<p><a href="https://doi.org/10.1088/0034-4885/72/7/076901">LIGO began operating</a> in the early 2000s, but it was not sensitive enough to detect gravitational waves. So, in 2010, the LIGO team temporarily shut down the facility to perform <a href="https://doi.org/10.1088/0264-9381/32/7/074001">upgrades to boost sensitivity</a>. The upgraded version of LIGO started <a href="https://theconversation.com/what-happens-when-ligo-texts-you-to-say-its-detected-one-of-einsteins-predicted-gravitational-waves-53259">collecting data in 2015 and almost immediately</a> <a href="https://doi.org/10.1103/PhysRevLett.116.061102">detected gravitational waves</a> produced from the merger of two black holes. </p>
<p>Since 2015, LIGO has completed <a href="https://observing.docs.ligo.org/plan/#timeline">three observation runs</a>. The first, run O1, lasted about four months; the second, O2, about nine months; and the third, O3, ran for 11 months before the COVID-19 pandemic forced the facilities to close. Starting with run O2, LIGO has been jointly observing with an <a href="https://doi.org/10.1088/0264-9381/32/2/024001">Italian observatory called Virgo</a>.</p>
<p>Between each run, scientists improved the physical components of the detectors and data analysis methods. By the end of run O3 in March 2020, researchers in the LIGO and Virgo collaboration had detected <a href="https://doi.org/10.48550/arXiv.2111.03606">about 90 gravitational waves</a> from the merging of black holes and neutron stars.</p>
<p>The observatories have still <a href="https://dcc.ligo.org/LIGO-P1200087/public">not yet achieved their maximum design sensitivity</a>. So, in 2020, both observatories shut down for upgrades <a href="https://www.ligo.caltech.edu/news/ligo20200326">yet again</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two people in white lab outfits working on complicated machinery." src="https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/527297/original/file-20230519-27-8k3n94.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Upgrades to the mechanical equipment and data processing algorithms should allow LIGO to detect fainter gravitational waves than in the past.</span>
<span class="attribution"><a class="source" href="https://www.ligo.caltech.edu/image/ligo20190326b">LIGO/Caltech/MIT/Jeff Kissel</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Making some upgrades</h2>
<p>Scientists have been working on <a href="https://dcc-llo.ligo.org/public/0182/G2200736/001/UpdateonLVKDetectors.pdf">many technological improvements</a>.</p>
<p>One particularly promising upgrade involved adding a 1,000-foot (300-meter) <a href="https://spie.org/news/photonics-focus/marapr-2023/squeezing-light-for-ligo?SSO=1">optical cavity</a> to improve a <a href="https://doi.org/10.1088/1361-6633/aab906">technique called squeezing</a>. Squeezing allows scientists to reduce detector noise using the quantum properties of light. With this upgrade, the LIGO team should be able to detect much weaker gravitational waves than before.</p>
<p><a href="https://igc.psu.edu/people/bio/crh184/#nav-members">My teammates and I</a> are data scientists in the LIGO collaboration, and we have been working on a number of different upgrades to <a href="https://doi.org/10.48550/arXiv.2305.05625">software used to process LIGO data</a> and the algorithms that recognize <a href="https://doi.org/10.48550/arXiv.2305.06286">signs of gravitational waves in that data</a>. These algorithms function by searching for patterns that match <a href="https://doi.org/10.48550/arXiv.2211.16674">theoretical models of millions</a> of possible black hole and neutron star merger events. The improved algorithm should be able to more easily pick out the faint signs of gravitational waves from background noise in the data than the previous versions of the algorithms.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A GIF showing a star brightening over a few days." src="https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=641&fit=crop&dpr=1 600w, https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=641&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=641&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=805&fit=crop&dpr=1 754w, https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=805&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/527298/original/file-20230519-27-h3pm1c.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=805&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Astronomers have captured both the gravitational waves and light produced by a single event, the merger of two neutron stars. The change in light can be seen over the course of a few days in the top right inset.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/press-release/nasa-missions-catch-first-light-from-a-gravitational-wave-event">Hubble Space Telescope, NASA and ESA</a></span>
</figcaption>
</figure>
<h2>A hi-def era of astronomy</h2>
<p>In early May 2023, LIGO began a short test run – called an engineering run – to make sure everything was working. On May 18, LIGO detected gravitational waves likely <a href="https://gcn.nasa.gov/circulars/33813">produced from a neutron star merging into a black hole</a>.</p>
<p>LIGO’s 20-month observation run 04 will officially <a href="https://www.ligo.org/news/images/ER15-newsitem.pdf">start on May 24,</a> and it will later be joined by Virgo and a new Japanese observatory – the Kamioka Gravitational Wave Detector, or KAGRA. </p>
<p>While there are many scientific goals for this run, there is a particular focus on detecting and localizing gravitational waves in real time. If the team can identify a gravitational wave event, figure out where the waves came from and alert other astronomers to these discoveries quickly, it would enable astronomers to point other telescopes that collect visible light, radio waves or other types of data at the source of the gravitational wave. Collecting multiple channels of information on a single event – <a href="https://doi.org/10.3847/1538-4357/ab0e8f">multi-messenger astrophysics</a> – is like adding color and sound to a black-and-white silent film and can provide a much deeper understanding of astrophysical phenomena.</p>
<p>Astronomers have only observed a single event <a href="https://doi.org/10.3847/2041-8213/aa91c9">in both gravitational waves and visible light</a> to date – the merger of <a href="https://theconversation.com/ligo-announcement-vaults-astronomy-out-of-its-silent-movie-era-into-the-talkies-85727">two neutron stars seen in 2017</a>. But from this single event, physicists were able to study the <a href="https://doi.org/10.1038/nature24471">expansion of the universe</a> and confirm the origin of some of the universe’s most energetic events known as <a href="https://doi.org/10.3847/2041-8213/aa920c">gamma-ray bursts</a>.</p>
<p>With run O4, astronomers will have access to the most sensitive gravitational wave observatories in history and hopefully will collect more data than ever before. My colleagues and I are hopeful that the coming months will result in one – or perhaps many – multi-messenger observations that will push the boundaries of modern astrophysics.</p><img src="https://counter.theconversation.com/content/204339/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chad Hanna receives funding from the National Science Foundation and NASA.</span></em></p>Upgrades to the hardware and software of the advanced observatory should allow astrophysicists to detect much fainter gravitational waves than before.Chad Hanna, Professor of Physics, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2049022023-05-11T20:08:05Z2023-05-11T20:08:05ZFlip-flopping magnetic fields hint at a solution for puzzling fast radio bursts from space<figure><img src="https://images.theconversation.com/files/525288/original/file-20230510-23-sjc51m.jpg?ixlib=rb-1.1.0&rect=1040%2C1047%2C2185%2C1429&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Fast radio bursts – intense, milliseconds-long flashes of radio energy from outer space – have <a href="https://www.pnas.org/doi/full/10.1073/pnas.1703512114">puzzled astronomers</a> since they were first spotted in 2007. A single burst can emit as much energy in its brief life as the Sun does in a few days.</p>
<p>The great majority of the short-lived pulses originate outside our Milky Way galaxy. We don’t know what produces most of them, or how. </p>
<p>In <a href="http://www.science.org/doi/10.1126/science.abo6526">new research published in Science</a>, we observed a repeating fast radio burst for more than a year and discovered signs it is surrounded by a strong but highly changeable magnetic field. </p>
<p>Our results suggest the source of this cosmic explosion may be a binary system made up of a neutron star whirling through winds of dense, magnetised plasma produced by a massive companion star or even a black hole.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/525534/original/file-20230511-21-ifg0v8.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An infographic with heading 'Twisted Fields Around Mysterious Fast Radio Burst' shows an illustration of two radio telescopes, a bright object in the sky, and a chart." src="https://images.theconversation.com/files/525534/original/file-20230511-21-ifg0v8.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/525534/original/file-20230511-21-ifg0v8.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/525534/original/file-20230511-21-ifg0v8.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/525534/original/file-20230511-21-ifg0v8.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/525534/original/file-20230511-21-ifg0v8.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/525534/original/file-20230511-21-ifg0v8.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/525534/original/file-20230511-21-ifg0v8.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">Changes in the magnetic field around a repeating fast radio burst hint at the nature of its origin.</span>
<span class="attribution"><span class="source">Di Li / ScienceApe / Chinese Academy of Science</span></span>
</figcaption>
</figure>
<h2>A fast radio burst that never stops repeating</h2>
<p>The repeating burst known as FRB 20190520B was <a href="https://www.nature.com/articles/s41586-022-04755-5">discovered in 2022</a> by astronomers at the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China. Repeating fast radio bursts are rare, but FRB 20190520B is the rarest of all: it is the only one that never rests, producing radio bursts a few times an hour, sometimes at multiple radio frequencies. </p>
<p>After this intriguing object was first found, astronomers rushed to follow up the initial observation using other radio wavelengths.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/more-bright-fast-radio-bursts-revealed-but-where-do-they-all-come-from-104488">More 'bright' fast radio bursts revealed, but where do they all come from?</a>
</strong>
</em>
</p>
<hr>
<p>Further investigation showed FRB 20190520B resides in an extremely dense environment in a dwarf galaxy 3.9 billion light years away. There are also materials surrounding the FRB source that produce strong, persistent radio emissions.</p>
<p>This led to suggestions that the bursting source is a young neutron star in a complex environment.</p>
<h2>Powerful magnetic fields</h2>
<p>What else can we learn about this intergalactic firecracker and its environment? We carried out observations of FRB 20190520B using CSIRO’s Parkes radio telescope, Murriyang, in New South Wales and the Green Bank Telescope in the United States. </p>
<p>To our surprise, FRB 20190520B turned out to produce strong signals at relatively high radio frequencies. These high-frequency signals turned out to be highly polarised - which means the electromagnetic waves are “waving” much more strongly in one direction than in others.</p>
<p>We found the direction of this polarisation changes at different frequencies. Measuring how much it changes tells us about the strength of the magnetic field the signal has travelled through. </p>
<p>As it turns out, this polarisation measure suggests the environment around FRB 20190520B is highly magnetised. And what’s more, the strength of the magnetic field appeared to vary over the 16 months we observed the source – and even flipped direction entirely twice. </p>
<p>This change in direction of the magnetic field around a fast radio burst has never been observed before.</p>
<h2>Filling in the picture</h2>
<p>What does this tell us about FRB 20190520B? Most popular theories to explain recent observations of repeating fast radio bursts involve binary systems made up of a neutron star and either another massive star or a black hole. </p>
<p>While we cannot rule out other hypotheses yet, our results favour the massive star scenario. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-brief-history-what-we-know-so-far-about-fast-radio-bursts-across-the-universe-154381">A brief history: what we know so far about fast radio bursts across the universe</a>
</strong>
</em>
</p>
<hr>
<p>Massive stars are known to have strong stellar winds with organised magnetic fields around them. If the source of the bursts were moving in and out of the stellar wind region as it travels through its orbit, we would expect the observed magnetic field direction to reverse. </p>
<p>The time scale of the magnetic field reversal, the measured variability in the apparent field strength, and the dense plasma surrounding the burst source all fit into this picture. </p>
<h2>What’s next?</h2>
<p>Our observations might provide crucial evidence to support the hypothesis that sources of repeating fast radio bursts have a massive companion capable of producing highly magnetised plasma. </p>
<p>More importantly, the binary hypothesis gives us a prediction for the future. If it is correct, the changes in polarisation of the radio signals from FRB 20190520B should rise and fall over longer periods of time. </p>
<p>So we will be watching. Future observations with Murriyang and the Green Bank Telescope will reveal whether FRB 20190520B is truly in a binary system – or whether the Universe will surprise us once again.</p><img src="https://counter.theconversation.com/content/204902/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shi Dai receives funding from the Australian Research Council. He is affiliated with CSIRO Space and Astronomy and the National Astronomical Observatory of China. </span></em></p><p class="fine-print"><em><span>Reshma Anna-Thomas receives funding from NSF grant AAG-1714897. Reshma Anna-Thomas is affiliated with Department of Physics and Astronomy and Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV, USA. </span></em></p><p class="fine-print"><em><span>Di Li and Miroslav Filipovic 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>Magnetic fields billions of light years away offer clues to the nature of intense flashes from the sky known as fast radio bursts.Shi Dai, ARC DECRA Fellow, Western Sydney UniversityDi Li, Professor, National Astronomical Observatories, Chinese Academy of SciencesMiroslav Filipovic, Professor, Western Sydney UniversityReshma Anna-Thomas, PhD candidate Department of Physics and Astronomy, West Virginia UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2023412023-03-27T19:00:47Z2023-03-27T19:00:47ZFor the first time, astronomers have linked a mysterious fast radio burst with gravitational waves<figure><img src="https://images.theconversation.com/files/517532/original/file-20230327-14-a7i9er.jpeg?ixlib=rb-1.1.0&rect=92%2C58%2C3138%2C1886&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">ASKAP.</span> <span class="attribution"><span class="source">CSIRO</span></span></figcaption></figure><p>We have <a href="https://www.nature.com/articles/s41550-023-01917-x">just published evidence</a> in Nature Astronomy for what might be producing mysterious bursts of radio waves coming from distant galaxies, known as <a href="https://theconversation.com/fast-radio-bursts-new-intergalactic-messengers-15700">fast radio bursts</a> or FRBs.</p>
<p>Two colliding <a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341#:%7E:text=Origin%20of%20a%20neutron%20star&text=Once%20its%20nuclear%20fuel%20is,the%20mass%20of%20our%20sun.">neutron stars</a> – each the super-dense core of an exploded star – produced a burst of gravitational waves when they merged into a “<a href="https://www.ozgrav.org/news/research-highlight-the-aftermath-of-binary-neutron-star-mergers">supramassive” neutron star</a>. We found that two and a half hours later they produced an FRB when the neutron star collapsed into a black hole.</p>
<p>Or so we think. The key piece of evidence that would confirm or refute our theory – an optical or gamma-ray flash coming from the direction of the fast radio burst – vanished almost four years ago. In a few months, we might get another chance to find out if we are correct.</p>
<h2>Brief and powerful</h2>
<p>FRBs are incredibly powerful pulses of radio waves from space lasting about a thousandth of a second. Using data from a radio telescope in Australia, the Australian Square Kilometre Array Pathfinder (<a href="https://www.csiro.au/ASKAP">ASKAP</a>), <a href="https://www.science.org/doi/10.1126/science.aaw5903">astronomers have found</a> that most FRBs come from galaxies so distant, light takes <a href="https://theconversation.com/how-we-closed-in-on-the-location-of-a-fast-radio-burst-in-a-galaxy-far-far-away-119177">billions of years to reach us</a>. But what produces these radio wave bursts has been puzzling astronomers since <a href="https://www.science.org/doi/10.1126/science.1147532">an initial detection</a> in 2007.</p>
<p>The best clue comes from an object in our galaxy known as SGR 1935+2154. It’s a <a href="https://earthsky.org/space/what-is-a-magnetar/">magnetar</a>, which is a neutron star with magnetic fields about a trillion times stronger than a fridge magnet. On April 28 2020, it produced a <a href="https://www.nature.com/articles/s41586-020-2872-x">violent burst of radio waves</a> – similar to an FRB, although less powerful.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-brief-history-what-we-know-so-far-about-fast-radio-bursts-across-the-universe-154381">A brief history: what we know so far about fast radio bursts across the universe</a>
</strong>
</em>
</p>
<hr>
<p>Astronomers have long predicted that two neutron stars – a binary – merging to produce a <a href="https://theconversation.com/explainer-black-holes-7431">black hole</a> should also produce a burst of radio waves. The two neutron stars will be highly magnetic, and black holes cannot have magnetic fields. <a href="https://www.aanda.org/articles/aa/full_html/2014/02/aa21996-13/aa21996-13.html">The idea</a> is the sudden vanishing of magnetic fields when the neutron stars merge and collapse to a black hole produces a fast radio burst. Changing magnetic fields produce electric fields – it’s how most power stations produce electricity. And the huge change in magnetic fields at the time of collapse could produce the intense electromagnetic fields of an FRB.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A black field with two illustrations of galaxies in the foreground, and a yellow beam connecting them" src="https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=387&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=387&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=387&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=487&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=487&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517530/original/file-20230327-14-ht1uqe.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=487&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s impression of a fast radio burst traveling through space and reaching Earth.</span>
<span class="attribution"><a class="source" href="https://www.eso.org/public/images/eso1915a/">ESO/M. Kornmesser</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>The search for the smoking gun</h2>
<p>To test this idea, Alexandra Moroianu, a masters student at the University of Western Australia, looked for merging neutron stars detected by the Laser Interferometer Gravitational-Wave Observatory (<a href="https://www.ligo.org/index.php">LIGO</a>) in the US. The gravitational waves LIGO searches for are ripples in spacetime, produced by the collisions of two massive objects, such as neutron stars.</p>
<p>LIGO has found two binary neutron star mergers. Crucially, the second, known as <a href="https://www.ligo.org/detections/GW190425.php">GW190425</a>, occurred when a new FRB-hunting telescope called <a href="https://chime-experiment.ca/en">CHIME</a> was also operational. However, being new, it took CHIME two years <a href="https://theconversation.com/535-new-fast-radio-bursts-help-answer-deep-questions-about-the-universe-and-shed-light-on-these-mysterious-cosmic-events-161976">to release its first batch of data</a>. When it did so, Moroianu quickly identified a fast radio burst called <a href="https://www.chime-frb.ca/catalog/FRB20190425A">FRB 20190425A</a> which occurred only two and a half hours after GW190425.</p>
<p>Exciting as this was, there was a problem – only one of LIGO’s two detectors was working at the time, making it <a href="https://theconversation.com/weve-detected-new-gravitational-waves-we-just-dont-know-where-they-come-from-yet-116267">very uncertain</a> where exactly GW190425 had come from. In fact, there was a 5% chance this could just be a coincidence.</p>
<p>Worse, the <a href="https://fermi.gsfc.nasa.gov/">Fermi</a> satellite, which could have detected gamma rays from the merger – the “smoking gun” confirming the origin of GW190425 – was <a href="https://link.springer.com/article/10.1134/S1063773719110057">blocked by Earth</a> at the time.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A nighttime view of white curved pipes arranged in a grid pattern" src="https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517525/original/file-20230326-14-fnkwc4.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">CHIME, the Canadian Hydrogen Intensity Mapping Experiment, has turned out to be uniquely suited to detecting FRBs.</span>
<span class="attribution"><span class="source">Andre Renard/Dunlap Institute/CHIME Collaboration</span></span>
</figcaption>
</figure>
<h2>Unlikely to be a coincidence</h2>
<p>However, the critical clue was that FRBs trace the total amount of gas they have passed through. We know this because high-frequency radio waves travel faster through the gas than low-frequency waves, so the time difference between them tells us the amount of gas.</p>
<p>Because we know the <a href="https://theconversation.com/half-the-matter-in-the-universe-was-missing-we-found-it-hiding-in-the-cosmos-138569">average gas density of the universe</a>, we can relate this gas content to distance, which is known as the <a href="https://www.nature.com/articles/s41586-020-2300-2">Macquart relation</a>. And the distance travelled by FRB 20190425A was a near-perfect match for the distance to GW190425. Bingo!</p>
<p>So have we discovered the source of all FRBs? No. There are not enough merging neutron stars in the Universe to explain the number of FRBs – some must still come from magnetars, like SGR 1935+2154 did.</p>
<p>And even with all the evidence, there’s still a one in 200 chance this could all be a giant coincidence. However, LIGO and two other gravitational wave detectors, <a href="https://www.virgo-gw.eu/">Virgo</a> and <a href="https://gwcenter.icrr.u-tokyo.ac.jp/en/">KAGRA</a>, will <a href="https://www.ligo.caltech.edu/page/observing-plans">turn back on</a> in May this year, and be more sensitive than ever, while CHIME and <a href="https://www.mwatelescope.org/">other radio telescopes</a> are ready to immediately detect any FRBs from neutron star mergers.</p>
<p>In a few months, we may find out if we’ve made a key breakthrough – or if it was just a flash in the pan.</p>
<hr>
<p><em>Clancy W. James would like to acknowledge Alexandra Moroianu, the lead author of the study; his co-authors, Linqing Wen, Fiona Panther, Manoj Kovalem (University of Western Australia), Bing Zhang and Shunke Ai (University of Nevada); and his late mentor, Jean-Pierre Macquart, who experimentally verified the gas-distance relation, which is now named after him.</em></p><img src="https://counter.theconversation.com/content/202341/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Clancy William James receives funding from the Australian Research Council. </span></em></p>For years, astronomers have been detecting incredibly powerful pulses from the cosmos, without a confirmed source. Recent advances in astronomy are getting us closer to the solution.Clancy William James, Senior Lecturer (astronomy and astroparticle physics), Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1968592022-12-21T13:40:49Z2022-12-21T13:40:49ZUnusual, long-lasting gamma-ray burst challenges theories about these powerful cosmic explosions that make gold, uranium and other heavy metals<figure><img src="https://images.theconversation.com/files/502241/original/file-20221220-20-5eta2v.jpeg?ixlib=rb-1.1.0&rect=70%2C601%2C2172%2C1591&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When two neutron stars merge and create a black hole, they produce a powerful blast of gamma rays.</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/14255"> A. Simonnet (Sonoma State Univ.) and NASA’s Goddard Space Flight Center</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p><em>The <a href="https://theconversation.com/us/topics/research-brief-83231">Research Brief</a> is a short take about interesting academic work.</em> </p>
<h2>The big idea</h2>
<p>A bright flash of gamma rays from the constellation Boötes that lasted nearly one minute came from a kilonova, as we described in <a href="https://doi.org/10.1038/s41586-022-05327-3">a new paper</a>. This finding challenges what astronomers know about some of the most powerful events in the universe.</p>
<p>The unusual cosmic explosion was detected by the <a href="https://www.nasa.gov/mission_pages/swift/main">Neil Gehrels Swift</a> observatory on Dec. 11, 2021, as the satellite orbited Earth. When astronomers pointed other telescopes at the part of the sky where this large blast of gamma rays – named GRB211211A – came from, they saw a glow of visible and infrared light known as a <a href="https://theconversation.com/we-beat-a-cyber-attack-to-see-the-kilonova-glow-from-a-collapsing-pair-of-neutron-stars-85660">kilonova</a>. The particular wavelengths of light coming from this explosion allowed our team to identify the source of the unusual gamma-ray burst as two neutron stars colliding and merging together.</p>
<p>Gamma rays are the most energetic form of electromagnetic radiation. In just a few seconds, a gamma-ray burst blasts out the same amount of energy that the Sun will radiate throughout <a href="https://www.scientificamerican.com/article/record-breaking-gamma-rays-reveal-secrets-of-the-universes-most-powerful-explosions/">its entire life</a>. Gamma-ray bursts are the <a href="https://theconversation.com/flash-aah-aah-could-a-gamma-ray-burst-eradicate-all-life-on-earth-5291">most powerful events in the universe</a>, and astronomers think only two cosmic scenarios can produce gamma-ray bursts.</p>
<p>The most common sources are the deaths of stars 30 to 50 times more massive than the Sun. The catastrophic destruction of one these large stars is called a <a href="https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-supernova.html">supernova</a>. When they explode, the stars create black holes that consume the leftover debris. These black holes emit a jet of matter and electromagnetic radiation that moves at close to the speed of light. In moments after the black hole starts emitting this high-energy stream of matter and radiation, the jet produces a burst of gamma rays that can last for minutes. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/502215/original/file-20221220-24-6x1y81.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of galaxies and stars in the sky with a graph showing brightness and duration." src="https://images.theconversation.com/files/502215/original/file-20221220-24-6x1y81.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/502215/original/file-20221220-24-6x1y81.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=624&fit=crop&dpr=1 600w, https://images.theconversation.com/files/502215/original/file-20221220-24-6x1y81.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=624&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/502215/original/file-20221220-24-6x1y81.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=624&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/502215/original/file-20221220-24-6x1y81.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=785&fit=crop&dpr=1 754w, https://images.theconversation.com/files/502215/original/file-20221220-24-6x1y81.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=785&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/502215/original/file-20221220-24-6x1y81.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=785&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 unusual gamma-ray burst originated from the small red dot within the circle in this image. The graph shows how bright and long-lasting the burst was.</span>
<span class="attribution"><span class="source">International Gemini Observatory/NOIRLab/NSF/AURA/M. Zamani/NASA/ESA/Eleonora Troja</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Kilonovae are the second type of events associated with gamma-ray bursts. Kilonovae occur when a neutron star merges with another neutron star or is consumed by a black hole. Neutron stars <a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">are rather small stars</a> – about 1.4 to 2 times the mass of the Sun, though only dozens of miles across.</p>
<p>When two of these tiny, dense stars merge to produce a black hole, they leave very little material behind. Compared with the long-lasting feast a black hole gets after a supernova, kilonovae leave a black hole with little more than a snack that results in a gamma-ray burst that lasts only a second or <a href="https://doi.org/10.1088/0004-637X/764/2/179">two at most</a>.</p>
<p>For over 20 years, astronomers thought that kilonovae accompanied short gamma-ray bursts and supernovae accompanied long ones. So when our team started looking at the wealth of data and images collected on the minute-long burst in December 2021, we expected to see a supernova. Much to our surprise, we found a kilonova.</p>
<h2>Why it matters</h2>
<p>Kilonovae are cosmic factories that <a href="https://theconversation.com/piercing-the-mystery-of-the-cosmic-origins-of-gold-88880">create heavy metals</a>, including gold, platinum, iodine and uranium. Because they enrich the chemical composition of the universe, kilonovae are critical to providing the basic ingredients for the formation of planets and life.</p>
<p>GRB211211A’s long duration <a href="https://doi.org/10.1038/d41586-022-04165-7">contradicts existing theories</a> of how gamma-ray bursts relate to supernovae and kilonovae. This finding shows that there is still a lot astronomers like us don’t understand about these powerful and important processes and suggests that there may be other ways the universe can produce heavy metals.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/FQLZPm34Chg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Kilonovae are responsible for producing heavy metals – like gold, uranium and iodine – that are important for many processes in the universe.</span></figcaption>
</figure>
<h2>What still isn’t known</h2>
<p>The initial images and data gathered on this interesting event look like a kilonova produced from the collision of two neutron stars. But the long-lasting burst of gamma rays throws doubt on what exactly happened. It is possible that one of the players was a rare neutron star with an <a href="https://apod.nasa.gov/apod/ap980527.html">incredibly powerful magnetic field</a> – called a magnetar. The burst could also have been the result of a neutron star being <a href="https://theconversation.com/what-happens-when-black-holes-collide-with-the-most-dense-stars-in-the-universe-162526">torn apart by its companion black hole</a>. Or astronomers could have just witnessed a <a href="https://doi.org/10.1038/s41586-022-05403-8">new, previously unknown type of stellar crash</a>. </p>
<h2>What’s next</h2>
<p>The few exotic stellar encounters that produce gamma-ray bursts can look very similar to one another across the electromagnetic spectrum. However, the unique gravitational wave signatures they produce could be the key to solving the enigma. The gravitational wave detectors <a href="https://www.ligo.org/">LIGO</a>, <a href="https://www.virgo-gw.eu/">Virgo</a> and <a href="https://gwcenter.icrr.u-tokyo.ac.jp/en/">KAGRA</a> did not see GRB211211A, as they were all offline for improvements. If they can catch a long-duration gamma-ray burst after they begin operating again in <a href="https://observing.docs.ligo.org/plan/">2023</a>, the <a href="https://doi.org/10.1038/s42254-019-0101-z">combination of gravitational wave and electromagnetic data</a> may solve the mystery of this newly discovered event.</p><img src="https://counter.theconversation.com/content/196859/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Eleonora Troja receives funding from the European Research Council under the European Union's Horizon 2020 research and innovation programme. </span></em></p><p class="fine-print"><em><span>Simone Dichiara does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Gamma-ray bursts occur when a massive star explodes or when two neutron stars merge. A newly discovered burst has puzzled astronomers, as it lasted much longer than astronomers would have expected.Eleonora Troja, Associate Professor of Astrophysics, University of Rome Tor VergataSimone Dichiara, Assistant Research Professor of Astrophysics, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1840502022-05-30T20:32:25Z2022-05-30T20:32:25ZThis newly discovered neutron star might light the way for a whole new class of stellar object<figure><img src="https://images.theconversation.com/files/465905/original/file-20220530-22-ktw8io.jpeg?ixlib=rb-1.1.0&rect=89%2C112%2C4902%2C3211&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>The discovery of a neutron star emitting unusual radio signals is rewriting our understanding of these unique star systems.</p>
<p>My colleagues and I (the <a href="https://www.meertrap.org/">MeerTRAP</a> team) made the discovery when observing the Vela-X 1 region of the Milky Way about 1,300 light years away from Earth, using the MeerKAT radio telescope in South Africa. We spotted a strange-looking flash or “pulse” that lasted about 300 milliseconds. </p>
<p>The flash had some characteristics of a radio-emitting neutron star. But this wasn’t like anything we’d seen before. </p>
<p>Intrigued, we scoured through older data from the region in hopes of finding similar pulses. Interestingly, we did identify more such pulses which had previously been missed by our real-time pulse detection system (since we typically only search for pulses lasting some 20-30 milliseconds).</p>
<p>A quick analysis of the times of arrival of the pulses showed them to be repeating about every 76 seconds – whereas <a href="https://www.skyatnightmagazine.com/space-science/neutron-star/">most neutron star</a> pulses cycle through within a few seconds, or even milliseconds.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram of a neutron star" src="https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=694&fit=crop&dpr=1 600w, https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=694&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=694&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=872&fit=crop&dpr=1 754w, https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=872&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=872&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Neutron stars are the collapsed cores of massive stars. Those that emit beams of electromagnetic radiation are classified as pulsars.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Our observation showed PSR J0941-4046 had some of the characteristics of a “pulsar” or even a “magnetar”. Pulsars are the extremely dense remnants of collapsed giant stars which usually emit radio waves from their poles. As they rotate, the radio pulses can be measured from Earth, a bit like how you’d see a lighthouse periodically flash in the distance.</p>
<p>However, the longest known rotation period for a pulsar before this was 23.5 seconds – which means we might have found a completely new class of radio-emitting object. Our findings are <a href="https://doi.org/10.1038/s41550-022-01688-x">published today</a> in Nature Astronomy.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-brief-history-what-we-know-so-far-about-fast-radio-bursts-across-the-universe-154381">A brief history: what we know so far about fast radio bursts across the universe</a>
</strong>
</em>
</p>
<hr>
<h2>An anomaly among neutron stars?</h2>
<p>Using all the data available to us from the MeerTRAP and <a href="http://www.thunderkat.uct.ac.za/">ThunderKAT</a> projects at MeerKAT, we managed to pinpoint the object’s position with excellent accuracy. After this we carried our more sensitive follow-up observations to study the source of the pulses. </p>
<p>The newly discovered object, named PSR J0941-4046, is a peculiar radio-emitting galactic neutron star which rotates extremely slowly compared to other pulsars. Pulsar pulse rates are incredibly consistent, and our follow-up observations allowed us to predict the arrival time of each pulse to a 100-millionth of a second.</p>
<p>Apart from the unexpected pulse rate, PSR J0941-4046 is also unique as it resides in the neutron star “graveyard”. This is a region of space where we don’t expect to detect any radio emissions at all, since it’s theorised the neutron stars here are at the end of their life cycle and therefore not active (or less active). PSR J0941-4046 challenges our understanding of how neutron stars are born and evolve.</p>
<p>It’s also fascinating as it appears to produce at least seven distinctly different pulse shapes, whereas most neutron stars don’t exhibit such variety. This diversity in pulse shape, and also pulse intensity, is likely related to the unknown physical emission mechanism of the object.</p>
<p>One particular type of pulse shows a strongly “quasi-periodic” structure, which suggests some kind of oscillation is driving the radio emission. These pulses may provide us with valuable information about the inner workings of PSR J0941-4046.</p>
<p>These quasi-periodic pulses bear some resemblance to enigmatic fast radio bursts, which are short radio bursts of unknown origin. However, it’s not yet clear whether PSR J0941-4046 emits the kind of energies observed in fast radio bursts. If we find it does, then it could be that PSR J0941-4046 is an “ultra-long period magnetar”.</p>
<p><a href="https://astronomy.swin.edu.au/cosmos/M/Magnetar">Magnetars</a> are neutron stars with very powerful magnetic fields, of which only a handful are known to emit in the radio part of the spectrum. While we’ve yet to actually identify an ultra-long period magnetar, they are theorised to be a possible source of fast radio bursts.</p>
<h2>Brief encounters</h2>
<p>It’s unclear how long PSR J0941-4046 has been active and emitting in the radio spectrum, since radio surveys typically don’t usually search for periods this long. </p>
<p>We don’t know how many of these sources might exist in the galaxy. Also, we can only detect radio emissions from PSR J0941-4046 for 0.5% of its rotation period – so it’s only visible to us for a fraction of a second. It’s pretty lucky we were able to spot it in the first place. </p>
<p>Detecting similar sources is challenging, which implies there may be a larger undetected population waiting to be discovered. Our finding also adds to the possibility of a new class of radio transient: the ultra-long period neutron star. Future searches for similar objects will be vital to our understanding of the neutron star population. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/this-object-in-space-flashed-brilliantly-for-3-months-then-disappeared-astronomers-are-intrigued-175240">This object in space flashed brilliantly for 3 months, then disappeared. Astronomers are intrigued</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/184050/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Manisha Caleb acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 694745), an Australian Research Council Discovery Early Career Research Award (project number DE220100819) funded by the Australian Government and the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. </span></em></p>The object has a highly unusually long rotation period, and was found in an area we call the neutron star ‘graveyard’.Manisha Caleb, Lecturer, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1752402022-01-26T19:03:24Z2022-01-26T19:03:24ZThis object in space flashed brilliantly for 3 months, then disappeared. Astronomers are intrigued<figure><img src="https://images.theconversation.com/files/442444/original/file-20220125-19-6p41pi.jpg?ixlib=rb-1.1.0&rect=22%2C49%2C2973%2C2946&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist visualisation</span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><blockquote>
<p>“Holy sharks, Batman, it’s periodic!” </p>
</blockquote>
<p>I exclaimed on Slack.</p>
<p>It was the first lockdown of 2021 in Perth, and we were all working from home. And when astronomers look for something to distract themselves from looming existential dread, there’s nothing better than a new cosmic mystery. </p>
<p>In 2020 I gave an undergraduate student, Tyrone O'Doherty, a fun project: look for radio sources that are changing in a <a href="https://www.ted.com/talks/natasha_hurley_walker_how_radio_telescopes_show_us_unseen_galaxies">large radio survey</a> I’m leading. </p>
<p>By the end of the year he’d found a particularly unusual source that was visible in data from early 2018, but had disappeared within a few months. The source <a href="https://www.nature.com/articles/s41586-021-04272-x">was named GLEAM-X J162759.5-523504</a>, after the survey it was found in and its position. </p>
<p>Sources that appear and disappear are called “radio transients” and are usually a sign of extreme physics at play. </p>
<h2>The mystery begins</h2>
<p>Earlier this year I started investigating the source, expecting it to be something we knew about – something that would change slowly over months and perhaps point to an exploded star, or a big collision in space. </p>
<p>To understand the physics, I wanted to measure how the source’s brightness relates to its frequency (in the electromagnetic spectrum). So I looked at observations of the same location, taken at different frequencies, before and after the detection, and it wasn’t there. </p>
<p>I was disappointed, as spurious signals do crop up occasionally due to telescope calibration errors, Earth’s ionosphere reflecting TV signals, or aircraft and satellites streaking overhead. </p>
<p>So I looked at more data. And in an observation taken 18 minutes later, there the source was again, in exactly the same place and at exactly the same frequency – like nothing astronomers had ever seen before.</p>
<p>At this point I broke out in a cold sweat. There is a worldwide research effort searching for repeating cosmic radio signals transmitted at a single frequency. It’s called the <a href="https://theconversation.com/curious-kids-what-has-the-search-for-extraterrestrial-life-actually-yielded-and-how-does-it-work-122454">Search for Extra-Terrestrial Intelligence</a>. Was this the moment we finally found that the truth is … <em>out there</em>?</p>
<figure>
<iframe src="https://player.vimeo.com/video/657269342" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">One of the brightest pulses from the new radio transient detected with the Murchison Widefield Array.</span></figcaption>
</figure>
<h2>The plot thickens</h2>
<p>I rapidly downloaded more data and posted updates on Slack. This source was incredibly bright. It was outshining everything else in the observation, which is nothing to sniff at. </p>
<p>The brightest radio sources are supermassive black holes flaring huge jets of matter into space at nearly the speed of light. What had we found that could possibly be brighter than that?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/experts-solve-the-mystery-of-a-giant-x-shaped-galaxy-with-a-monster-black-hole-as-its-engine-138205">Experts solve the mystery of a giant X-shaped galaxy, with a monster black hole as its engine</a>
</strong>
</em>
</p>
<hr>
<p>Colleagues were beginning to take notice, posting:</p>
<blockquote>
<p>It’s repeating too slowly to be a pulsar. But it’s too bright for a flare star. What is this? (alien emoji icon)??? </p>
</blockquote>
<p>Within a few hours, I breathed a sigh of relief: I had detected the source across a wide range of frequencies, so the power it would take to generate it could only come from a natural source; not artificial (and not aliens)! </p>
<p>Just like <a href="https://www.space.com/32661-pulsars.html">pulsars</a> – highly magnetised rotating neutron stars that beam out radio waves from their poles – the radio waves repeated like clockwork about three times per hour. In fact, I could predict when they would appear to an accuracy of one ten-thousandth of a second.</p>
<p>So I turned to our enormous data archive: 40 petabytes of radio astronomy data recorded by the Murchison Widefield Array in Western Australia, during its eight years of operation. Using <a href="https://pawsey.org.au/">powerful supercomputers</a>, I searched hundreds of observations and picked up 70 more detections spanning three months in 2018, but none before or after.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/tuning-in-to-cosmic-radio-from-the-dawn-of-time-51584">Tuning in to cosmic radio from the dawn of time</a>
</strong>
</em>
</p>
<hr>
<p>The amazing thing about radio transients is that if you have enough frequency coverage, you can work out how far away they are. This is because lower radio frequencies arrive slightly later than higher ones depending on how much space they’ve traveled through. </p>
<p>Our new discovery lies about 4,000 light years away – very distant, but still in our galactic backyard.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/442445/original/file-20220125-13-54xe4a.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/442445/original/file-20220125-13-54xe4a.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/442445/original/file-20220125-13-54xe4a.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/442445/original/file-20220125-13-54xe4a.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/442445/original/file-20220125-13-54xe4a.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/442445/original/file-20220125-13-54xe4a.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/442445/original/file-20220125-13-54xe4a.gif?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">Interstellar space slows down long wavelength radio waves more than short.</span>
<span class="attribution"><span class="source">ICRAR</span></span>
</figcaption>
</figure>
<p>We also found the radio pulses were almost completely <a href="https://www.sciencefocus.com/science/what-is-polarised-light/">polarised</a>. In astrophysics this usually means their source is a strong magnetic field. The pulses were also changing shape in just half a second, so the source has to be less than half a light second across, much smaller than our Sun.</p>
<p>Sharing the result with colleagues across the world, everyone was excited, but no one knew for sure what it was.</p>
<h2>The jury is still out</h2>
<p>There were two leading explanations for this compact, rotating, and highly magnetic astrophysical object: a white dwarf, or a neutron star. These remain after stars run out of fuel and collapse, generating magnetic fields billions to quintillions times stronger than our Sun’s. </p>
<p>And while we’ve never found a neutron star that behaves quite this way, theorists have predicted such objects, called an “ultra-long period magnetars”, could exist. Even so, no one expected one could be so bright.</p>
<figure>
<iframe src="https://player.vimeo.com/video/657248792" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">We think the source could be either a magnetar or a white dwarf, or something completely unknown.</span></figcaption>
</figure>
<p>This is the first time we’ve ever seen a radio source that repeats every 20 minutes. But maybe the reason we never saw one before is that we weren’t looking.</p>
<p>When I first started trying to understand this source, I was biased by my expectations: transient radio sources either change quickly like pulsars, or slowly like the fading remnants of a supernova.</p>
<p>I wasn’t looking for sources repeating at 18-minute intervals – an unusual period for any known class of object. Nor was I searching for something that would appear for a few months and then disappear forever. No one was.</p>
<p>As astronomers build <a href="https://www.skatelescope.org/">new</a> <a href="https://www.lsst.org/">telescopes</a> that will collect vast quantities of data, it’s vital we keep our minds, and our search techniques, open to unexpected possibilities. The universe is full of wonders, should we only choose to look.</p><img src="https://counter.theconversation.com/content/175240/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Natasha Hurley-Walker is supported by an Australian Research Council Future Fellowship (project number FT190100231) funded by the Australian Government.</span></em></p>A mysterious repeating signal from our galactic backyard is a reminder the universe is full of unexpected surprises, if only we should look.Natasha Hurley-Walker, Radio Astronomer, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1731572021-12-13T19:07:29Z2021-12-13T19:07:29ZWe counted 20 billion ticks of an extreme galactic clock to give Einstein’s theory of gravity its toughest test yet<figure><img src="https://images.theconversation.com/files/435995/original/file-20211207-21-1w4a3pw.jpeg?ixlib=rb-1.1.0&rect=142%2C146%2C2578%2C2004&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of the Double Pulsar system in which the two pulsars orbit each other every 2.5 hours and send out high-energy beams that sweep across the sky.</span> <span class="attribution"><a class="source" href="https://sites.google.com/site/johnroweanimation/home">Image credit: John Rowe Animations/CSIRO</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>For more than 100 years, Albert Einstein’s general theory of relativity has been our best description of how the force of gravity acts throughout the Universe.</p>
<p>General relativity is not only very accurate, but ask any astrophysicist about the theory and they’ll probably also describe it as “beautiful”. But it has a dark side too: a fundamental conflict with our other great physical theory, quantum mechanics.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-einsteins-theory-of-general-relativity-3481">Explainer: Einstein's Theory of General Relativity</a>
</strong>
</em>
</p>
<hr>
<p>General relativity works extremely well at large scales in the Universe, but quantum mechanics rules the microscopic realm of atoms and fundamental particles. To resolve this conflict, we need to see general relativity pushed to its limits: extremely intense gravitational forces at work on small scales.</p>
<p>We studied a pair of stars called the Double Pulsar which provide just such a situation. After 16 years of observations, we have found <a href="https://journals.aps.org/prx/abstract/10.1103/PhysRevX.11.041050">no cracks in Einstein’s theory</a>. </p>
<h2>Pulsars: nature’s gravity labs</h2>
<p>In 2003, astronomers at CSIRO’s Parkes radio telescope, Murriyang, in New South Wales <a href="https://www.atnf.csiro.au/research/highlights/2003/manchester/manchester.html">discovered</a> a double pulsar system 2,400 light years away that offers a perfect opportunity to study general relativity under extreme conditions. </p>
<p>To understand what makes this system so special, imagine a star 500,000 times as heavy as Earth, yet only 20 kilometres across. This ultra-dense “neutron star” spins 50 times a second, blasting out an intense beam of radio waves that our telescopes register as a faint blip every time it sweeps over Earth. There are more than 3,000 such “pulsars” in the Milky Way, but this one is unique because it whirls in an orbit around a similarly extreme companion star every 2.5 hours.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/fifty-years-ago-jocelyn-bell-discovered-pulsars-and-changed-our-view-of-the-universe-88083">Fifty years ago Jocelyn Bell discovered pulsars and changed our view of the universe</a>
</strong>
</em>
</p>
<hr>
<p>According to general relativity, the colossal accelerations in the Double Pulsar system strain the fabric of space-time, sending gravitational ripples away at the speed of light that slowly sap the system of orbital energy. </p>
<p>This slow loss of energy makes the stars’ orbit drift ever closer together. In 85 million years’ time, they are doomed to merge in a spectacular cosmic pile-up that will enrich the surroundings with a <a href="https://theconversation.com/cosmic-alchemy-colliding-neutron-stars-show-us-how-the-universe-creates-gold-86104">heady dose of precious metals</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/437086/original/file-20211213-23-yur4x4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/437086/original/file-20211213-23-yur4x4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/437086/original/file-20211213-23-yur4x4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/437086/original/file-20211213-23-yur4x4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/437086/original/file-20211213-23-yur4x4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/437086/original/file-20211213-23-yur4x4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/437086/original/file-20211213-23-yur4x4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of the Double Pulsar system and its effect on spacetime. The spacetime curvature (shown in the grid at the bottom) is highest near the pulsars. As they orbit one another, these deformations propagate away at the speed of light as gravity waves, carrying away orbital energy. By counting each time the pulsed beam of radio emission sweeps over the Earth, we can track the slowly shrinking orbit.</span>
<span class="attribution"><span class="source">Image credit: M. Kramer / MPIfR</span></span>
</figcaption>
</figure>
<p>We can watch this loss of energy by very carefully studying the blinking of the pulsars. Each star acts as a giant clock, precisely stabilised by its immense mass, “ticking” with every rotation as its radio beam sweeps past. </p>
<h2>Using stars as clocks</h2>
<p>Working with an international team of astronomers led by Michael Kramer of the Max Planck Institute for Radio Astronomy in Germany, we have used this “pulsar timing” technique to study the Double Pulsar ever since its discovery.</p>
<p>Adding in data from five other radio telescopes across the world, we modelled the precise arrival times of more than 20 billion of these clock ticks over a 16-year period. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/435538/original/file-20211203-13-1z06w8u.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/435538/original/file-20211203-13-1z06w8u.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=414&fit=crop&dpr=1 600w, https://images.theconversation.com/files/435538/original/file-20211203-13-1z06w8u.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=414&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/435538/original/file-20211203-13-1z06w8u.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=414&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/435538/original/file-20211203-13-1z06w8u.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=521&fit=crop&dpr=1 754w, https://images.theconversation.com/files/435538/original/file-20211203-13-1z06w8u.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=521&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/435538/original/file-20211203-13-1z06w8u.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=521&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Parkes 64-metre diameter radio telescope, located in Central NSW, Australia, was used to observe the pulsed radio emission.</span>
<span class="attribution"><span class="source">Image credit: Shaun Amy/CSIRO</span></span>
</figcaption>
</figure>
<p>To complete our model, we needed to know exactly how far the Double Pulsar is from Earth. To find this out, we turned to a global network of ten radio telescopes called the Very Long Baseline Array (VLBA).</p>
<p>The VLBA has such high resolution it could spot a human hair 10km away! Using it, we were able to observe a tiny wobble in the apparent position of the Double Pulsar every year, which results from Earth’s motion around the Sun. </p>
<p>And because the size of the wobble depends on the distance to the source, we could show that the system is 2,400 light years from the Earth. This provided the last puzzle piece we needed to put Einstein to the test.</p>
<h2>Finding Einstein’s fingerprints in our data</h2>
<p>Combining these painstaking measurements allows us to precisely track the orbits of each pulsar. Our benchmark was Isaac Newton’s simpler model of gravity, which predated Einstein by several centuries: every deviation offered another test. </p>
<p>These “post-Newtonian” effects – things that are insignificant when considering an apple falling from a tree, but noticeable in more extreme conditions – can be compared against the predictions of general relativity and other theories of gravity.</p>
<p>One of these effects is the loss of energy due to gravitational waves described above. Another is the “<a href="https://cosmosmagazine.com/space/catching-frame-dragging-in-action/">Lense-Thirring effect</a>” or “relativistic frame-dragging”, in which the spinning pulsars drag space-time itself around with them as they move.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/warp-factor-weve-observed-a-spinning-star-that-drags-the-very-fabric-of-space-and-time-130201">Warp factor: we've observed a spinning star that drags the very fabric of space and time</a>
</strong>
</em>
</p>
<hr>
<p>In total, we detected seven post-Newtonian effects, including some never seen before. Together, they give by far the best test so far of general relativity in strong gravitational fields.</p>
<p>After 16 long years, <a href="https://journals.aps.org/prx/abstract/10.1103/PhysRevX.11.041050">our observations</a> proved to be amazingly consistent with Einstein’s general relativity, matching Einstein’s predictions to within 99.99%. None of the dozens of other gravitational theories proposed since 1915 can describe the motion of the Double Pulsar better!</p>
<p>With larger and more sensitive radio telescopes, and new analysis techniques, we could keep using the Double Pulsar to study gravity for another 85 million years. Eventually, however, the two stars will spiral together and merge. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/435781/original/file-20211206-104971-1rcisdi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/435781/original/file-20211206-104971-1rcisdi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=532&fit=crop&dpr=1 600w, https://images.theconversation.com/files/435781/original/file-20211206-104971-1rcisdi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=532&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/435781/original/file-20211206-104971-1rcisdi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=532&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/435781/original/file-20211206-104971-1rcisdi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=669&fit=crop&dpr=1 754w, https://images.theconversation.com/files/435781/original/file-20211206-104971-1rcisdi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=669&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/435781/original/file-20211206-104971-1rcisdi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=669&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s illustration of two merging neutron stars, which is the fate of the Double Pulsar in 85 million years’ time. Such collisions can be detected by gravitational wave laser interferometers, and provide a complementary test of general relativity.</span>
<span class="attribution"><span class="source">Image credit: NSF/LIGO/Sonoma State University/A. Simonnet</span></span>
</figcaption>
</figure>
<p>This cataclysmic ending will itself offer one last opportunity, as the system throws off a burst of high-frequency gravitational waves. Such bursts from merging neutron stars in other galaxies have already been detected by the LIGO and Virgo gravitational-wave observatories, and those measurements provide a complementary test of general relativity under even more extreme conditions.</p>
<p>Armed with all these approaches, we are hopeful of eventually identifying a weakness in general relativity that can lead to an even better gravitational theory. But for now, Einstein still reigns supreme.</p><img src="https://counter.theconversation.com/content/173157/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adam Deller receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Richard Manchester has received funding from the Australian Research Council.</span></em></p>Astronomers watched a pair of pulsars for 16 years to test the theory of general relativity, which has stood unchallenged for over a century.Adam Deller, Associate Investigator, ARC Centre of Excellence for Gravitational Waves (OzGrav), and Associate Professor in Astrophysics, Swinburne University of TechnologyRichard Manchester, CSIRO Fellow, CSIRO Space and Astronomy, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1639862021-07-07T20:07:49Z2021-07-07T20:07:49ZWe found a new type of stellar explosion that could explain a 13-billion-year-old mystery of the Milky Way’s elements<figure><img src="https://images.theconversation.com/files/410093/original/file-20210707-21-qxb5cu.jpeg?ixlib=rb-1.1.0&rect=50%2C13%2C2196%2C1404&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NASA/WikiCommons</span></span></figcaption></figure><p>Until recently it was thought neutron star mergers were the only way <a href="https://pls.llnl.gov/research-and-development/nuclear-science/project-highlights/livermorium/elements-113-and-115">heavy elements</a> (heavier than Zinc) could be produced. These mergers involve the mashup of the remnants of two massive stars in a binary system. </p>
<p>But we know heavy elements were first produced not long after the Big Bang, when the universe was really young. Back then, not enough time had passed for neutron star mergers to have even occurred. Thus, another source was needed to explain the presence of early heavy elements in the Milky Way.</p>
<p>The discovery of an ancient star SMSS J2003-1142 in the Milky Way’s halo — which is the roughly spherical region that surrounds the galaxy — is providing the first evidence for another source for heavy elements, including uranium and possibly gold. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/410107/original/file-20210707-13-vbdmhd.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/410107/original/file-20210707-13-vbdmhd.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/410107/original/file-20210707-13-vbdmhd.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=647&fit=crop&dpr=1 600w, https://images.theconversation.com/files/410107/original/file-20210707-13-vbdmhd.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=647&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/410107/original/file-20210707-13-vbdmhd.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=647&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/410107/original/file-20210707-13-vbdmhd.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=813&fit=crop&dpr=1 754w, https://images.theconversation.com/files/410107/original/file-20210707-13-vbdmhd.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=813&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/410107/original/file-20210707-13-vbdmhd.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=813&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Around our galaxy, the Milky Way, there is a ‘halo’ made up of hot gases which is continually being supplied with material ejected by birthing or dying stars. Only 1% of stars in the galaxy are found in the halo.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>In our research <a href="https://dx.doi.org/10.1038/s41586-021-03611-2">published today</a> in Nature, we show the heavy elements detected in SMSS J2003-1142 were likely produced, not by a neutron star merger, but through the collapse and explosion of a rapidly spinning star with a strong magnetic field and a mass about 25 times that of the Sun.</p>
<p>We call this explosion event a “magnetorotational hypernova”. </p>
<h2>Stellar alchemy</h2>
<p>It was recently <a href="https://www.space.com/strontium-heavy-element-formed-neutron-star-merger.html">confirmed</a> that neutron star mergers are indeed one source of the heavy elements in our galaxy. As the name suggests, this is when two neutron stars in a binary system merge together in an energetic event called a “kilonova”. This process produces heavy elements.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/410108/original/file-20210707-25-uv3eud.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/410108/original/file-20210707-25-uv3eud.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/410108/original/file-20210707-25-uv3eud.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/410108/original/file-20210707-25-uv3eud.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/410108/original/file-20210707-25-uv3eud.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/410108/original/file-20210707-25-uv3eud.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/410108/original/file-20210707-25-uv3eud.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/410108/original/file-20210707-25-uv3eud.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">Binary star systems have two stars orbiting around a common centre of mass. A neutron star merger is a type of stellar collision that happens between two neutron stars in a binary system. This process can produce heavy elements.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>However, existing models of the chemical evolution of our galaxy indicate that neutron star mergers <em>alone</em> could not have produced the specific patterns of elements we see in multiple ancient stars, including SMSS J2003-1142.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/signals-from-a-spectacular-neutron-star-merger-that-made-gravitational-waves-are-slowly-fading-away-94294">Signals from a spectacular neutron star merger that made gravitational waves are slowly fading away</a>
</strong>
</em>
</p>
<hr>
<h2>A relic from the early universe</h2>
<p>SMSS J2003-1142 was first observed in 2016 from Australia, and then again in September 2019 using a telescope at the European Southern Observatory in Chile.</p>
<p>From these observations, we studied the star’s chemical composition. Our analysis revealed an iron content roughly 3,000 times lower than the Sun’s. In other words, SMSS J2003-1142 is chemically primitive. </p>
<p>The elements we observed in it were likely produced by a single parent star, just after the Big Bang. </p>
<h2>Signatures of a collapsed rapidly spinning star</h2>
<p>The chemical composition of SMSS J2003-1142 can reveal the nature and properties of its parent star. Particularly important are its unusually high amounts of nitrogen, zinc and heavy elements including europium and uranium. </p>
<p>The high nitrogen levels in SMSS J2003-1142 indicate the parent star had rapid rotation, while high zinc levels indicate the energy of the explosion was about ten times that of a “normal” supernova — which means it would have been a hypernova. Also, large amounts of uranium would have required the presence of lots of neutrons. </p>
<p>The heavy elements we can observe in SMSS J2003-1142 today are all evidence that this star was produced as a result of an early magnetorotational hypernova explosion.</p>
<p>And our work has therefore provided the first evidence that magnetorotational hypernova events are a source of heavy elements in our galaxy (alongside neutron star mergers).</p>
<h2>What about neutron star mergers?</h2>
<p>But how do we know it wasn’t just neutron star mergers that led to the particular elements we find in SMSS J2003-1142? There’s a few reasons for this.</p>
<p>In our hypothesis, a single parent star would have made all the elements observed in SMSS J2003-1142. On the other hand, it would have taken much, much longer for the same elements to have been made only through neutron star mergers. But this time wouldn’t have even existed this early in the galaxy’s formation when these elements were made.</p>
<p>Also, neutron star mergers make <em>only</em> heavy elements, so additional sources such as regular supernova would had to have occurred to explain other heavy elements, such as calcium, observed in SMSS J2003-1142. This scenario, while possible, is more complicated and therefore less likely.</p>
<p>The magnetorotational hypernovae model not only provides a better fit to the data, it can also explain the composition of SMSS J2003-1142 through a single event. It could be neutron star mergers, together with magnetorotational supernovae, could in unison explain how all the heavy elements in the Milky Way were created. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-race-to-find-even-more-new-elements-to-add-to-the-periodic-table-52747">The race to find even more new elements to add to the periodic table</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/163986/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Yong receives funding from the Australian Research Council. He is affiliated with the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D). </span></em></p><p class="fine-print"><em><span>Gary Da Costa has received funding from the Australian Research Council. He is affiliated with the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D).</span></em></p>The discovery of an ancient star in the Milky Way’s halo is providing evidence for another source that would have produced the galaxy’s heavy elements.David Yong, Academic, Research School of Astronomy and Astrophysics, Australian National UniversityGary Da Costa, Emeritus Professor of Astronomy, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1625262021-06-30T14:02:05Z2021-06-30T14:02:05ZWhat happens when black holes collide with the most dense stars in the universe<p>For the first time, a faint signal caused by the merging of two almost equally mysterious objects – a black hole and a neutron star – has <a href="https://iopscience.iop.org/article/10.3847/2041-8213/ac082e">been recorded on Earth</a>.</p>
<p>On January 5 2020, when the world was first learning of the COVID-19 outbreak, gravitational waves from this merging reached the Livingston detector of the <a href="https://www.ligo.caltech.edu/page/what-is-ligo">Laser Interferometer Gravitational-wave Observatory (Ligo</a>) gravitational wave observatory in Louisiana, US. </p>
<p>On January 15, the second gravitational wave event from a merger between a black hole and a neutron star, the densest stars in the universe, was discovered.</p>
<p>These two recordings are the first mergers between a black hole and a neutron star to have been detected on Earth. Black hole-neutron star binary systems, where a black hole and a neutron star orbit each other, <a href="https://www.frontiersin.org/articles/10.3389/fspas.2020.00046/full">had been predicted</a> but never observed – until now.</p>
<p><a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">Gravitational waves</a> are distortions in space-time, predicted by Albert Einstein’s general theory of relativity. </p>
<p>In a <a href="https://theconversation.com/five-myths-about-gravitational-waves-46493">gravitational wave observatory</a>, the distance between two suspended mirrors is measured with a laser. The measurement technique relies on the overlap of reflected laser light within the experiment. Two light waves are arranged so that the signals cancel each other out exactly. Changing the distance between the mirrors by even a tiny fraction of a wavelength produces a measurable light signal.</p>
<p>The basic idea behind the theory of relativity is that space itself possesses a kind of elastic structure, even in the absence of any matter. Similar to an inflated balloon, you can squeeze it one way and it expands in the perpendicular direction. </p>
<p>Relativity predicts that matter warps space (and time) and a collision between two compact objects like a black hole and a neutron star rapidly changes the compression and relaxation of the space in the vicinity of the objects. Waves of periodic compression and expansion are emitted. The way to measure these waves is to monitor the distance between two otherwise fixed objects, because the gravitational wave will periodically change the extent of the space between these objects, as it passes.</p>
<p>During the first ever detected gravitational wave event in 2015, for which three physicists were awarded <a href="https://theconversation.com/scientists-behind-the-discovery-of-gravitational-waves-win-the-2017-nobel-prize-for-physics-66457">the Nobel prize in 2017</a>, the distances between the mirrors in the two stations of the LIGO observatory, which are 4km (2.5 miles) apart, changed by about a thousandth of a trillionth of a millimetre. </p>
<p>The merger detected in 2015 was between two comparatively massive black holes, each around 30 times the mass of the Sun. Since then, the sensitivity of the instrument has been improved. Now also a smaller, less sensitive, gravitational wave observatory in Italy, called <a href="https://www.virgo-gw.eu/">the Virgo experiment</a>, is frequently used as part of the telescope network. </p>
<p>In the new discoveries, the merging objects each had less than ten times the mass of the Sun. The event on January 5 involved objects with respective masses of 8.9 and 1.9 times the mass of the Sun, and the merger on January 15 was between objects with 5.7 and a 1.5 times the mass of the Sun.</p>
<h2>Neutron stars</h2>
<p>It’s important that the smaller masses were below 2.2 times the mass of the Sun, because this suggests these objects were neutron stars. Neutron stars are so dense that an amount of matter comparable to the solar system is compressed to a diameter of about 20km.</p>
<p>The matter in a neutron star is so dense that atoms get crushed, resulting in the formation of neutrons. The strong gravity on their surface makes them, in their own right, interesting laboratories to study effects of general relativity. </p>
<p>When a neutron star becomes even more massive, for example when some interstellar gas falls on it, the nuclear forces can no longer resist gravity and the star collapses to a black hole, an object so compact that not even light can resist its gravitational pull.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal-85647">How we discovered gravitational waves from 'neutron stars' – and why it's such a huge deal</a>
</strong>
</em>
</p>
<hr>
<p>Neutron stars and black holes are not that rare in the Milky Way. They are a common outcome from the evolution of stars significantly more massive than the Sun. Such massive stars often occur in binary systems, with two stars orbiting each other.</p>
<p>It’s not surprising to find neutron stars and black holes in binary systems, where they are locked in a gravitational dance. Such binaries emit gravitational waves for their entire lifetime.</p>
<h2>Binary systems</h2>
<p>The energy for the gravitational waves comes from the motion of the objects around each other. As the system emits gravitational waves, the objects get closer together. This makes the gravitational wave emission increase and, finally, the two merge into a new, bigger black hole, with a burst of gravitational wave emission. This is what is detectable on Earth.</p>
<p>While it was expected that neutron star-black hole systems existed, we’d never been able to spot them before. Neutron stars emit radio and X-ray emissions, which can now be routinely detected. Other than looking for gravitational waves, black holes can only be observed when something falls on them – a star or interstellar gas, for example.</p>
<p>If a black hole has a normal star companion, it can capture mass from the companion which emits X-rays before it disappears into the black hole. Binary black holes have no obvious source of gas, and they’re known only from gravitational wave experiments. </p>
<p>A neutron star-black hole system could in principle be discovered with radio telescopes, but – so far – the search has not been successful. This new discovery provides important information about the astrophysics of such systems. </p>
<p>More discoveries will surely be made, which will help to improve our understanding of what is inside neutron stars and black holes – and quite possibly also provide new tests, or proofs, of the theory of relativity.</p><img src="https://counter.theconversation.com/content/162526/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Martin Krause receives funding from the Science and Technology Facilities Council and is a fellow of the Royal Astronomical Society, member of the Astronomische Gesellschaft, the European Astronomical Society, the International Astronomical Union and the German Physical Society.</span></em></p>The aftermath of a black hole colliding with a neutron star has been recorded on Earth.Martin Krause, Senior Lecturer, University of HertfordshireLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1635752021-06-29T12:07:28Z2021-06-29T12:07:28Z‘Laws of nature turned up to 11’: astronomers spot two neutron stars being swallowed by black holes<figure><img src="https://images.theconversation.com/files/408783/original/file-20210629-19-11qb29b.jpg?ixlib=rb-1.1.0&rect=1%2C9%2C1304%2C912&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Carl Knox/OzGrav/Swinburne Univ.</span></span></figcaption></figure><p>One of the best things about being an astronomer is being able to discover something new about the universe. In fact, maybe the only thing better is discovering it twice. And that’s exactly what my colleagues and I have done, by making two separate observations, just ten days apart, of an entirely new type of astronomical phenomenon: a neutron star circling a black hole before being gobbled up.</p>
<p>The two observations were made in January 2020, by the <a href="https://www.ligo.caltech.edu/page/what-is-ligo">Laser Interferometer Gravitational-wave Observatory (LIGO)</a> and the <a href="https://www.virgo-gw.eu/">Virgo Observatory</a>, both of which detect gravitational waves from the distant cosmos. </p>
<p>After 18 months of painstaking analysis, our discoveries are <a href="https://doi.org/10.3847/2041-8213/ac082e">published today in The Astrophysics Journal Letters</a>. The new observations open up new avenues to study the life cycle of stars, the nature of space-time, and the behaviour of matter at extreme pressures and densities.</p>
<p>The first observation of a neutron star-black hole system was made on January 5 2020. LIGO and Virgo observed gravitational waves — distortions in the very fabric of space-time — produced by the final 30 seconds of the dying orbit of the neutron star and black hole, followed by their inevitable collision. The discovery is named GW200105. </p>
<p>Remarkably, just ten days later, LIGO and Virgo detected gravitational waves from a second collision between a neutron star and a black hole. This event is named GW200115. Both collisions happened around 900 million years ago, long before the first dinosaurs appeared on Earth.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/dACjwnMhUJg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Artist’s impression of a neutron star orbiting and colliding with a black hole – Carl Knox/OzGrav/Swinburne Univ.</span></figcaption>
</figure>
<p>Neutron stars and black holes are among the most extreme objects in the universe. They are the fossil relics of massive dead stars. When a star that is more than eight times as massive as the Sun runs out of fuel, it undergoes a spectacular explosion called a supernova. What remains can be a neutron star or a black hole. </p>
<p>Neutron stars are typically between 1.5 and 2 times as massive as the Sun, but are so dense that all their mass is packed into an object the size of a city. At this density, atoms can no longer sustain their structure, and dissolve into a stream of free quarks and gluons: the building blocks of protons and neutrons.</p>
<p>Black holes are even more extreme. There is no upper limit to how massive a black hole can be, but all black holes have two things in common: a point of no return at their surface called an “event horizon”, from which not even light can escape; and a point at their centre called a “singularity”, at which the laws of physics as we understand them break down. </p>
<p>It is fair to say black holes are an enigma. One of the holy grails of 21st-century physics and astronomy is to find a deeper understanding of the laws of nature by observing these strange and extreme objects.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">Gravitational waves discovered: the universe has spoken</a>
</strong>
</em>
</p>
<hr>
<h2>A new type of star system</h2>
<p>Neutron stars orbiting black hole companions have long been thought to exist. LIGO and Virgo had been searching for them for more than a decade, but they have remained elusive until now.</p>
<p>So why are we so confident we’ve now seen not one such system, but two? </p>
<p>When LIGO and Virgo observe gravitational waves, the first question on our minds is “what caused them?” To find that out, we use two things: our observational data, and supercomputer simulations of different types of astronomical events that could plausibly explain those data. </p>
<p>By comparing the simulations to our real observations, we look for those characteristics that best match our data, homing in on the likely ones and ruling out the unlikely ones.</p>
<p>For the first discovery (GW200105), we determined that the most likely source of the gravitational waves was the final few orbits, and eventual collision, between an object around 8.9 times the mass of the Sun, with an object around 1.9 times the mass of the Sun. Given the masses involved, the most plausible explanation is that the heavier object is a black hole, and the lighter one is a neutron star. </p>
<p>Similarly, from the second (GW200115), we determined that its most likely source was the final few orbits and collision of a 5.7-solar-mass black hole with a 1.5-solar-mass neutron star.</p>
<p>There is no definitive smoking gun that the lighter objects are neutron stars, and in principle they could be very light black holes, although we consider this explanation unlikely. By far the best hypothesis is that our new observations are consistent with the merger of neutron stars and black holes.</p>
<h2>Stellar fossil-hunting</h2>
<p>Our discoveries have several intriguing implications. Neutron star-black hole systems allow us to piece together the evolutionary history of stars. Gravitational-wave astronomers are like stellar fossil-hunters, using the relics of exploded stars to understand how massive stars form, live and die. </p>
<p>We have been doing this for several years with LIGO/Virgo’s observations of <a href="https://theconversation.com/when-black-holes-meet-inside-the-cataclysms-that-cause-gravitational-waves-54236">pairs of black holes</a> and <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">pairs of neutron stars</a>. The newly discovered rarer pairs, containing one of each, are fascinating pieces of the stellar fossil record. </p>
<p>For the first time we have directly measured the rate at which neutron stars merge with black holes: we think there are likely to be tens or hundreds of thousands such collisions across the universe per year. With more observations, we will measure the rate more precisely.</p>
<p>What happens to the neutron stars after they’ve been gobbled up? Now we’re really looking at the laws of nature turned up to 11. When neutron stars merge with black holes, they are deformed, imprinting information about their exotic form of matter onto the gravitational waves we observe on Earth. </p>
<p>This can reveal the composition of neutron stars, which in turn tells us about how quarks and gluons behave at extreme pressure and density. It doesn’t tell us what’s going on behind the black hole’s event horizon, although another aspect of our discoveries is that we can look for hints of new physics in black holes in the gravitational-wave signals.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/when-black-holes-meet-inside-the-cataclysms-that-cause-gravitational-waves-54236">When black holes meet: inside the cataclysms that cause gravitational waves</a>
</strong>
</em>
</p>
<hr>
<p>When LIGO and Virgo resume observing in mid-2022 after an upgrade to boost their sensitivity still further, we will see more collisions between neutron stars and black holes. In the coming decade we expect to amass thousands more gravitational-wave detections. </p>
<p>Over time we hope to piece together the laws of nature that will help us understand the inner workings of the most extreme and impenetrable objects in the universe.</p><img src="https://counter.theconversation.com/content/163575/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rory Smith does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Gravitational waves reveal the demise of super-dense neutron stars spiralling into their black hole companions - the first time such strange and exotic star systems have ever been observed.Rory Smith, Lecturer in Astrophysics, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1551252021-02-15T18:51:20Z2021-02-15T18:51:20ZA tiny crystal device could boost gravitational wave detectors to reveal the birth cries of black holes<figure><img src="https://images.theconversation.com/files/384196/original/file-20210215-15-u84vo1.jpg?ixlib=rb-1.1.0&rect=8%2C13%2C2986%2C2645&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NSF / LIGO / Sonoma State University / A Simonnet</span>, <span class="license">Author provided</span></span></figcaption></figure><p>In 2017, astronomers witnessed the birth of a black hole for the first time. Gravitational wave detectors picked up the ripples in spacetime caused by <a href="https://en.wikipedia.org/wiki/GW170817">two neutron stars colliding</a> to form the black hole, and other telescopes then observed the resulting explosion.</p>
<p>But the real nitty-gritty of how the black hole formed, the movements of matter in the instants before it was sealed away inside the black hole’s event horizon, went unobserved. That’s because the gravitational waves thrown off in these final moments had such a high frequency that our current detectors can’t pick them up.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">At last, we've found gravitational waves from a collapsing pair of neutron stars</a>
</strong>
</em>
</p>
<hr>
<p>If you could observe ordinary matter as it turns into a black hole, you would be seeing something similar to the Big Bang played backwards. The scientists who design gravitational wave detectors have been hard at work to figure out how improve our detectors to make it possible.</p>
<p>Today our team is publishing <a href="https://www.nature.com/articles/s42005-021-00526-2">a paper</a> that shows how this can be done. Our proposal could make detectors 40 times more sensitive to the high frequencies we need, allowing astronomers to listen to matter as it forms a black hole.</p>
<p>It involves creating weird new packets of energy (or “quanta”) that are a mix of two types of quantum vibrations. Devices based on this technology could be added to existing gravitational wave detectors to gain the extra sensitivity needed.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=369&fit=crop&dpr=1 600w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=369&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=369&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=464&fit=crop&dpr=1 754w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=464&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=464&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 conception of photons interacting with a millimetre scale phononic crystal device placed in the output stage of a gravitational wave detector.</span>
<span class="attribution"><span class="source">Carl Knox / OzGrav / Swinburne University</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Quantum problems</h2>
<p>Gravitational wave detectors such as the <a href="https://en.wikipedia.org/wiki/LIGO">Laser Interferometer Gravitational-wave Observatory (LIGO)</a> in the United States use lasers to measure incredibly small changes in the distance between two mirrors. Because they measure changes 1,000 times smaller than the size of a single proton, the effects of quantum mechanics – the physics of individual particles or quanta of energy – play an important role in the way these detectors work.</p>
<p>Two different kinds of quantum packets of energy are involved, both predicted by Albert Einstein. In 1905 he predicted that light comes in packets of energy that we call <em>photons</em>; two years later, he predicted that heat and sound energy come in packets of energy called <em>phonons</em>. </p>
<p>Photons are used widely in modern technology, but phonons are much trickier to harness. Individual phonons are usually swamped by vast numbers of random phonons that are the heat of their surroundings. In gravitational wave detectors, phonons bounce around inside the detector’s mirrors, degrading their sensitivity.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/australias-part-in-the-global-effort-to-discover-gravitational-waves-54525">Australia's part in the global effort to discover gravitational waves</a>
</strong>
</em>
</p>
<hr>
<p>Five years ago physicists realised you could <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.211104">solve the problem</a> of insufficient sensitivity at high frequency with devices that <em>combine</em> phonons with photons. They showed that devices in which energy is carried in quantum packets that share the properties of both phonons and photons can have quite remarkable properties. </p>
<p>These devices would involve a radical change to a familiar concept called “resonant amplification”. Resonant amplification is what you do when you push a playground swing: if you push at the right time, all your small pushes create big swinging.</p>
<p>The new device, called a “white light cavity”, would amplify all frequencies equally. This is like a swing that you could push any old time and still end up with big results.</p>
<p>However, nobody has yet worked out how to make one of these devices, because the phonons inside it would be overwhelmed by random vibrations caused by heat.</p>
<h2>Quantum solutions</h2>
<p>In <a href="https://www.nature.com/articles/s42005-021-00526-2">our paper</a>, published in Communications Physics, we show how two different projects currently under way could do the job.</p>
<p>The Niels Bohr Institute in Copenhagen has been <a href="https://www.nature.com/articles/nnano.2017.101">developing devices</a> called phononic crystals, in which thermal vibrations are controlled by a crystal-like structure cut into a thin membrane. The Australian Centre of Excellence for Engineered Quantum Systems has also demonstrated <a href="https://www.nature.com/articles/srep02132">an alternative system</a> in which phonons are trapped inside an ultrapure quartz lens.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=415&fit=crop&dpr=1 600w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=415&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=415&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=521&fit=crop&dpr=1 754w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=521&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=521&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of a tiny device that could boost gravitational wave detector sensitivity in high frequencies.</span>
<span class="attribution"><span class="source">Carl Knox / OzGrav / Swinburne University</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We show both of these systems satisfy the requirements for creating the “negative dispersion” – which spreads light frequencies in a reverse rainbow pattern – needed for white light cavities. </p>
<p>Both systems, when added to the back end of existing gravitational wave detectors, would improve the sensitivity at frequencies of a few kilohertz by the 40 times or more needed for listening to the birth of a black hole.</p>
<h2>What’s next?</h2>
<p>Our research does not represent an instant solution to improving gravitational wave detectors. There are enormous experimental challenges in making such devices into practical tools. But it does offer a route to the 40-fold improvement of gravitational wave detectors needed for observing black hole births.</p>
<p>Astrophysicists have predicted <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.100.043005">complex gravitational waveforms</a> created by the convulsions of neutron stars as they form black holes. These gravitational waves could allow us to listen in to the nuclear physics of a collapsing neutron star. </p>
<p>For example, it has been shown that they can clearly reveal whether the neutrons in the star remain as neutrons or whether they <a href="https://en.wikipedia.org/wiki/Quark_star">break up into a sea of quarks</a>, the tiniest subatomic particles of all. If we could observe neutrons turning into quarks and then disappearing into the black hole singularity, it would be the exact reverse of the Big Bang where out of the singularity, the particles emerged which went on to create our universe.</p><img src="https://counter.theconversation.com/content/155125/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Blair receives funding from the Australian Research Council. </span></em></p>A small add-on to existing gravitational wave detectors could reveal what happens to matter as it becomes a black hole, a process like the big bang in reverse.David Blair, Emeritus Professor, ARC Centre of Excellence for Gravitational Wave Discovery, OzGrav, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1276992019-11-25T14:34:10Z2019-11-25T14:34:10ZNew type of star system? Mysterious radio signal puzzles astronomers<figure><img src="https://images.theconversation.com/files/303437/original/file-20191125-74599-sltvmi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Meerkat telescope</span> <span class="attribution"><span class="source">Sotiris Sanidas</span>, <span class="license">Author provided</span></span></figcaption></figure><p>After observing a part of the sky near the <a href="https://www.universetoday.com/19574/ara/">Southern Constellation of Ara</a> for about two months using <a href="https://www.ska.ac.za/gallery/meerkat/">MeerKAT</a>, a radio telescope based in the Karoo desert in South Africa, <a href="http://www.thunderkat.uct.ac.za/">our team of scientists</a> noticed something strange. The radio emission of an object brightened by a factor of three over roughly three weeks. </p>
<p>Intrigued, we continued watching the object and followed this up with observations from other telescopes. We discovered that the unusual flare came from a <a href="https://www.space.com/22509-binary-stars.html">binary star system </a> – two stars orbiting each other – in our own galaxy. The finding, <a href="https://academic.oup.com/mnras/article/491/1/560/5610241">published in the Monthly Notices of the Royal Astronomical Society</a>, has, however, turned out to be very difficult to explain.</p>
<p>This is MeerKAT’s first discovery of a “transient source” – an object that is not constant, either undergoing a significant change in brightness or coming in and out of view altogether. Given the catchy name “MKT J170456.2-482100”, it was found in the first field observed with the telescope, which means it is likely to be the tip of an iceberg of transients waiting to be discovered.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/303500/original/file-20191125-74580-16dnqjj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/303500/original/file-20191125-74580-16dnqjj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=514&fit=crop&dpr=1 600w, https://images.theconversation.com/files/303500/original/file-20191125-74580-16dnqjj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=514&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/303500/original/file-20191125-74580-16dnqjj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=514&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/303500/original/file-20191125-74580-16dnqjj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=646&fit=crop&dpr=1 754w, https://images.theconversation.com/files/303500/original/file-20191125-74580-16dnqjj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=646&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/303500/original/file-20191125-74580-16dnqjj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=646&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Radio emission detected during the measurement, with the flare circled.</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>To understand our discovery, we started by matching our source with the position of a star, called TYC 8332-2529-1, about 1,800 light years from Earth. Because this star is relativity bright, we anticipated that a number of different optical telescopes – detecting visible light rather than radio waves – would have observed this star in the past. </p>
<p>Luckily, this turned out to be the case, allowing us to use such data to find out more about the star. It is a giant – about two and a half times the mass of the Sun. Some of the optical telescopes, including <a href="http://www.astronomy.ohio-state.edu/%7Eassassin/index.shtml">ASAS</a>, <a href="https://en.wikipedia.org/wiki/Kilodegree_Extremely_Little_Telescope">KELT</a> and <a href="http://www.astronomy.ohio-state.edu/%7Eassassin/index.shtml">ASAS-SN</a>, provided us with over 18 years of observations of the star. These helped us discover that the brightness of the star changes over a period of 21 days. We think this is because the star has large spots on it, just like sunspots. </p>
<p>We used the <a href="https://www.salt.ac.za/">SALT telescope</a> to obtain optical spectra of the star – similar to using a prism to split white light into its constituent wavelengths. This can be used to determine the chemical elements present in the star, as well as the presence of a magnetic field. What’s more, they enable scientists to tell if a star is moving, as movement causes these spectral lines to shift (Doppler shift). </p>
<p>The spectra revealed that the star has a magnetic field, and that it orbits a companion star every 21 days. However, we can only see a very faint, possible signature of the companion star in our observations so far. This tells us that the companion must be much fainter than the giant star. We also found, however, that the companion is likely to have at least 1.5 times the mass of the Sun. </p>
<p>So what could the companion be? A <a href="https://imagine.gsfc.nasa.gov/science/objects/dwarfs2.html">white dwarf</a> (a cold, dead star) may seem likely, as they are often part of binary star systems like this. However, most white dwarfs have a smaller mass than the companion we spotted – with a maximum mass of 1.6 times the mass of the Sun. So it is unlikely to be such a star.</p>
<h2>The plot thickens</h2>
<p>The radio flare itself could be caused by magnetic activity of the giant star, similar to solar flares but much brighter and more energetic. However, such flares are usually observed on dwarf stars rather than giant stars. </p>
<p><a href="https://en.wikipedia.org/wiki/RS_Canum_Venaticorum_variable">Known star systems</a> involving a giant star and a Sun-like star could explain the findings – with the magnetic activity of the giant star giving rise to flares. However, this doesn’t fit, as there is no sign in the spectra that the binary companion is actually a Sun-like star.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/303408/original/file-20191125-74542-10rtzae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/303408/original/file-20191125-74542-10rtzae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/303408/original/file-20191125-74542-10rtzae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/303408/original/file-20191125-74542-10rtzae.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/303408/original/file-20191125-74542-10rtzae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/303408/original/file-20191125-74542-10rtzae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/303408/original/file-20191125-74542-10rtzae.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">MeerKAT radio telescope.</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><a href="http://www.jodrellbank.manchester.ac.uk/people/staff/profile/?ea=Ben.Stappers">Ben Stappers</a>, principal investigator of <a href="https://www.MeerTRAP.org">MeerTRAP</a>, one of the teams working on the project, said that because the properties of the system don’t easily fit into our current knowledge of binary or flaring stars, it “may represent an entirely new source class”. We suspect that this might be some sort of exotic system that we have never seen before involving a radio-flaring giant star orbiting a neutron star (the dense remnant of a supernova star explosion) or a black hole.</p>
<p>MeerKAT is going to continue observing this source every week for the next four years, with the <a href="http://www.astronomy.ohio-state.edu/%7Eassassin/index.shtml">ASAS-SN optical telescope</a> continuing to observe the giant star. This means we will be able to explore the physics and nature of this source and its flares for many years to come.</p>
<p>This will tell us about the dynamics of this system, how flares occur and ultimately help us investigate how it formed. As MeerKAT continues to search the sky, we hope that this is the first of many new and unusual sources waiting to be discovered.</p><img src="https://counter.theconversation.com/content/127699/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Laura Nicole Driessen is part of MeerTRAP, which is based at the University of Manchester and receives funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 694745). </span></em></p>Radio flare may be the result of a giant star orbiting some unusual object – a combination we have never seen before.Laura Nicole Driessen, PhD candidate in Radio Astronomy, University of ManchesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1198612019-07-11T12:55:43Z2019-07-11T12:55:43ZJoy Division: 40 years on from ‘Unknown Pleasures’, astronomers have revisited the pulsar from the iconic album cover<figure><img src="https://images.theconversation.com/files/283650/original/file-20190711-173325-1oj4n2t.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C6000%2C3314&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">'Unknown Pleasures' as you've never seen it before...</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/3d-illustration-rendering-black-white-line-1308510430?src=E285f9LBp2pjGmUMJk8lMw-1-49&studio=1">Freeda/Shutterstock</a></span></figcaption></figure><p>The English rock band Joy Division released their debut studio album “Unknown Pleasures” 40 years ago. The front cover doesn’t feature any words, only a now iconic black and white data graph showing 80 wiggly lines representing a signal from a pulsar in space. To mark the anniversary of the album, we recorded a signal from the same pulsar with a radio telescope in Jodrell Bank Observatory, only 14 miles (23 km) away from Strawberry Studios where the album was recorded.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"497303154279845888"}"></div></p>
<p>Peter Saville – graphic designer and co-founder of Factory Records – designed the album cover based on a picture spotted by band member Bernard Sumner in an encyclopaedia. The picture itself can be traced to the work of the postgraduate student Harold Craft, who published the image in his PhD thesis in 1970. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282539/original/file-20190703-126376-b9s5nm.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Recording of the same pulsar, exactly 40 years after the album was released.</span>
<span class="attribution"><span class="source">Jodrell Bank Centre for Astrophysics, University of Manchester</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Unknown treasures in space</h2>
<p>What we see in this enigmatic image is the signal produced by a pulsar known as B1919+21, the first pulsar ever discovered. A pulsar is formed during the violent death of a star several times more massive than our sun. These stars go out with a bang known as a “supernova explosion”, during which the core of the exploding star is compressed in an almost perfect sphere with a radius of little more than 10 km. What’s formed is called a neutron star.</p>
<p>This stellar remnant, still more massive than our sun, is so extremely dense that the atoms from the original star cannot maintain their structure – they fall apart leaving smaller particles called neutrons, which form a vast ocean beneath the star’s crust. Pulsars are rapidly spinning neutron stars that can be observed from Earth. Thanks to their rotation and a magnetic field which is a trillion times stronger than that of the Earth, the magnetic north and south poles of these super magnets shine like a lighthouse. After having travelled for many hundreds of years, flashes of radiation from B1919+21 reach the Earth every 1.34 seconds.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1140000363367546882"}"></div></p>
<p>These flashes from pulsars are especially bright at radio wavelengths, so their signals can be recorded using radio telescopes. A radio telescope works similar to a radio in your car – its antenna focuses radio waves from space onto a point where they can be detected and turned into an electric signal, which can then be converted into sound. We used the Mark II radio telescope of the <a href="http://www.jb.man.ac.uk/research/pulsar/Education/Sounds/">Jodrell Bank Observatory</a> at the University of Manchester for our recording.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282898/original/file-20190705-51297-1fdtu7k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Mark II telescope at the Jodrell Bank Observatory which made a 47-minute recording of B1919+21.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Mark_II_(radio_telescope)#/media/File:Jodrell_Bank_Mark_II.jpg">Mike Peel/Jodrell Bank Centre for Astrophysics, University of Manchester</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The album cover shows 80 wiggly lines which correspond to 80 flashes of radio waves from B1919+21, as the neutron star made 80 turns in 107 seconds. Unlike lighthouses on Earth, each flash is unique. Some flashes are bright – these are denoted in the image by their large spikes – and some are dim. </p>
<p>The shape of the pulses are ever changing. At first glance, they seem irregular and chaotic, but our new imaging reveals some order in the chaos. It’s the same number of pulses from the same pulsar and observed at the same frequency as the diagram from the album cover, but in the image below, a diagonal pattern of stripes emerges.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=914&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=914&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=914&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1148&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1148&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282538/original/file-20190703-126382-wi9gtv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1148&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The signal of the same pulsar as featured on the album cover. The lighter the colour is, the more intense the radio waves are.</span>
<span class="attribution"><span class="source">Jodrell Bank Centre for Astrophysics, University of Manchester</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>When the original signal was recorded, it was not known why some pulsars showed this kind of pattern. We now believe that the radio waves are produced by particles which shoot away from the neutron star at nearly the speed of light. The particles are created by electric discharges between the ionised gas surrounding these objects and the surface of the star itself. So, in essence, the radio waves on the album cover and in our new imaging are caused by lightning in outer space, observed many light years away. </p>
<p>A “weather map” can help visualise the vast lightning systems which circulate the magnetic poles of pulsars. The pattern of their lightning changes continuously and the shape of the observed pulses appear somewhat erratic – but observing over a longer period allows a pattern to emerge.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=599&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=599&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=599&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=752&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=752&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282537/original/file-20190703-126360-ag3ko1.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=752&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Looking down on the magnetic pole of pulsar B1919+21 which is encircled by lightning.</span>
<span class="attribution"><span class="source">Jodrell Bank Centre for Astrophysics, University of Manchester</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Four decades after the release of the Unknown Pleasures album we now understand much better what those wiggly lines on its cover mean. But many questions remain about these enigmatic objects, which in many respects are nature’s most extreme creation. Something which remained true for all these years is that pulsar recordings push us to explore the limits of our understanding of the laws of physics.</p><img src="https://counter.theconversation.com/content/119861/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Patrick Weltevrede receives funding from the UK Science and Technology Facilities Council (STFC)</span></em></p>When you look at the squiggly lines on Joy Division’s famous album cover, you’re seeing a record of lightning in outer space.Patrick Weltevrede, Lecturer In Pulsar Astrophysics, University of ManchesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1162672019-05-03T05:53:05Z2019-05-03T05:53:05ZWe’ve detected new gravitational waves, we just don’t know where they come from (yet)<figure><img src="https://images.theconversation.com/files/272121/original/file-20190501-117601-6mspoo.jpg?ixlib=rb-1.1.0&rect=425%2C189%2C3144%2C1782&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A visualisation of a binary neutron star merger.</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/12740">NASA's Goddard Space Flight Center/CI Lab</a></span></figcaption></figure><p>The hunt for <a href="https://theconversation.com/au/topics/gravitational-waves-9473">gravitational waves</a> is back on with the <a href="https://www.ligo.caltech.edu/news/ligo20190502">announcement overnight</a> of the detection of signals from what’s thought to be the merger of two <a href="http://astronomy.swin.edu.au/cosmos/N/Neutron+Star">neutron stars</a>, the incredibly dense remains of a collapsed star.</p>
<p>The signals were actually picked up on Thursday April 25 — ANZAC Day here in Australia — from a binary merger named <a href="https://gracedb.ligo.org/superevents/S190425z/view/">S190425z</a>), only the second ever neutron star merger to be observed. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1121351752626909184"}"></div></p>
<p>The twin detectors of the Laser Interferometer Gravitational-Wave Observatory (<a href="https://www.ligo.caltech.edu/page/ligo-detectors">LIGO</a>) — in Washington and Louisiana in the United States — along with Virgo, located at the European Gravitational Observatory (<a href="http://www.ego-gw.it/public/virgo/virgo.aspx">EGO</a>) in Italy, only resumed their operations on April 1 after a year and a half of upgrades. The latest result shows the hunt is back with a bang. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/signals-from-a-spectacular-neutron-star-merger-that-made-gravitational-waves-are-slowly-fading-away-94294">Signals from a spectacular neutron star merger that made gravitational waves are slowly fading away</a>
</strong>
</em>
</p>
<hr>
<p>This is the third observing run (named O3) and soon after the merger signal was detected, astronomers around the world started searching for a host galaxy, but this time there was an extra challenge.</p>
<h2>Where is the signal coming from?</h2>
<p>When LIGO detects <a href="http://astronomy.swin.edu.au/cosmos/G/Gravitational+Waves">gravitational waves</a> — the ripples in space-time predicted by Albert Einstein — we can work out some information quite accurately, such as the mass of merging neutron stars.</p>
<p>The images (below) of all the signals detected in the first and second observing runs of the detectors (named O1 and O2) show how each signal is unique. These differences allow us to work out the masses and distances to the objects.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=342&fit=crop&dpr=1 600w, https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=342&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=342&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=430&fit=crop&dpr=1 754w, https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=430&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/271925/original/file-20190501-39926-j0843w.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=430&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Gravitational wave events detected by LIGO before O3. Each signal is different, revealing the properties of the merging objects.</span>
<span class="attribution"><a class="source" href="https://www.ligo.org/detections/O1O2catalog.php">LIGO/VIrgo/Georgia Tech/S. Ghonge & K. Jani</a></span>
</figcaption>
</figure>
<p>But one thing that is harder to work out is <em>where</em> the signal is coming from?</p>
<p>We do this by triangulating the signal received at the three detectors (the two LIGO detectors in the US and the Virgo detector in Italy).</p>
<p>For the first detection of merging binary neutron stars, <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.161101" title="GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral">GW170817</a>, we got lucky. We were able to narrow down the signal to a region of 28 square degrees on the sky (about 140 times the area of the full Moon).</p>
<p>But S190425z was only detected in a single LIGO detector and Virgo, and hence the localisation region was 10,000 square degrees. That’s about a quarter of the entire sky.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/271926/original/file-20190501-39956-1y9s9ft.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">LIGO localisation for the neutron star merger S190425z. The area covers about a quarter of the entire sky.</span>
<span class="attribution"><span class="source">LIGO</span></span>
</figcaption>
</figure>
<p>The neutron star merger is also estimated to have happened about 500 million light-years away from Earth. </p>
<h2>Needle in a haystack</h2>
<p>Astronomers around the world, including Australian teams, have been using telescopes from the outback of Western Australia to The Canary Islands in the Atlantic Ocean, to search for possible counterparts: galaxies that could be hosting the neutron star merger.</p>
<p>To do this we had to work out which of the 45,000 possible galaxies in the region would be the most likely hosts.</p>
<p>No confirmed matches have been found, so far, but on the way, we’ve found lots of other interesting events such as new supernovae - the explosions that occur when massive stars die.</p>
<p>This effort is an integral part of the Australian gravitational-wave hunting team at <a href="https://www.ozgrav.org/">OzGrav</a>. OzGrav supports more than 100 scientists and engineers who are making critical contributions to improving LIGO instrumentation, data analysis software, and interpretation of the results.</p>
<h2>How far can LIGO see now?</h2>
<p>The recent upgrades of LIGO and Virgo mean astronomers can now detect gravitational waves from binary neutron star mergers further than ever before, up to 500 million light years away.</p>
<p>Any signals we detect from these distant mergers would have left their host galaxy around the time the first fish evolved on Earth (two hundred million years before dinosaurs came along).</p>
<p>Every second counts when astronomers are trying to use gravitational wave triggers to capture the last moments as neutron stars collide. </p>
<p>The team at the University of Western Australia node of OzGrav has developed a real-time search program (called “SPIIR”) to trigger gravitational waves from the LIGO-Virgo data within ten seconds. </p>
<p>The team has already identified four gravitational-wave candidates, and in the future it may even be possible to eventually alert astronomers before the emission of any light from a merger.</p>
<h2>Beating the noise</h2>
<p>An important part of the LIGO O3 upgrade was the installation of instruments called “quantum squeezers”. The squeezers are based on an Australian National University design and ANU OzGrav scientists were part of the team that installed and commissioned them.</p>
<p>One of the most significant engineering challenges in building LIGO is reducing noise that can drown out the miniscule gravitational-wave signals. This noise comes from many different sources, such as seismic noise from earthquakes, ocean waves and even vehicle traffic.</p>
<p>Another source of noise is quantum noise, due to the discrete nature of light. The squeezers dampen this quantum noise by changing the quantum properties of the light used by LIGO to detect ripples in the fabric of spacetime. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272118/original/file-20190501-117582-1i6qqvl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">LIGO team members (left-to-right: Fabrice Matichard, Sheila Dwyer, Hugh Radkins) install in-vacuum equipment as part of the squeezed-light upgrade.</span>
<span class="attribution"><span class="source">Nutsinee Kijbunchoo/ANU</span></span>
</figcaption>
</figure>
<h2>Another event detected</h2>
<p>With the third observing run now well underway, we’re already seeing the results of these improvements to LIGO instrumentation and software.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-we-found-a-white-dwarf-a-stellar-corpse-by-accident-114089">How we found a white dwarf – a stellar corpse – by accident</a>
</strong>
</em>
</p>
<hr>
<p>In addition to the technical improvements there’s another marked contrast with previous observing runs: all detections are being released to the astronomy community, and the wider public, straight away. </p>
<p>In the midst of the excitement about S190425z there was <a href="https://gracedb.ligo.org/superevents/S190426c/view/">another gravitational-wave alert</a> a day later - a candidate signal with properties that suggest it could be a merger of a neutron star and a black hole.</p>
<p>This was picked up by all three detectors but as yet we also have no host identified for this, so we are not yet sure of the nature of this event. But it’s another hint of the exciting results yet to come.</p><img src="https://counter.theconversation.com/content/116267/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tara Murphy works for the University of Sydney. She receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Eric Thrane works for Monash University. He receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Qi Chu works for the University of Western Australia. She receives funding from Australian Research Council.</span></em></p>The signal came in on ANZAC Day, ripples in space-time from the merger of two neutron stars an estimated 500-million light years away. But where it happened is still a mystery.Tara Murphy, Professor, University of SydneyEric Thrane, Associate professor, Monash UniversityQi Chu, Research fellow, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1079622018-12-03T13:06:06Z2018-12-03T13:06:06ZNew detections of gravitational waves brings the number to 11 – so far<figure><img src="https://images.theconversation.com/files/248354/original/file-20181203-194928-1wx57ti.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ripples in space-time caused by massive events such this artist rendition of a pair of merging neutron stars.</span> <span class="attribution"><span class="source">Carl Knox, OzGrav</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Four new detections of gravitational waves have been announced at the <a href="https://www.elisascience.org/news/conferences/gravitational-wave-physics-and-astronomy-workshop-gwpaw">Gravitational Waves Physics and Astronomy Workshop</a>, at the University of Maryland in the United States. </p>
<p>This brings the total number of detections to 11, since the first <a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">back in 2015</a>.</p>
<p>Ten are from binary black hole mergers and one from the merger of two neutron stars, which are the dense remains of stellar explosions. One black hole merger was extraordinarily distant, and the most powerful explosion ever observed in astronomy.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-search-for-the-source-of-a-mysterious-fast-radio-burst-comes-relatively-close-to-home-105735">The search for the source of a mysterious fast radio burst comes relatively close to home</a>
</strong>
</em>
</p>
<hr>
<p>The latest news comes just a month after doubts were raised about the initial detection. In late October an article in New Scientist, headlined <a href="https://www.newscientist.com/article/mg24032022-600-exclusive-grave-doubts-over-ligos-discovery-of-gravitational-waves/">Exclusive: Grave doubts over LIGO’s discovery of gravitational waves</a>, raised the idea that it “might have been an illusion”. </p>
<p>So how confident are we that we are detecting gravitational waves, and not seeing an illusion?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/248361/original/file-20181203-194944-1pglcj3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s conception shows two merging black holes.</span>
<span class="attribution"><span class="source">LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)</span></span>
</figcaption>
</figure>
<h2>Open to scrutiny</h2>
<p>All good scientists understand that scrutiny and scepticism is the power of science. All theories and all knowledge are provisional, as science slowly homes in on our best understanding of the truth. There is no certainty, only probability and statistical significance. </p>
<p>Years ago the team searching for gravitational waves with the Laser Interferometer Gravitational-Wave Observatory (LIGO), determined the levels of statistical significance needed to make a claim of detection. </p>
<p>For each signal we determine the false alarm rate. This tells you how many years you would need to wait before you have an even chance of a random signal mimicking your real signal.</p>
<p>The weakest signal detected so far has a false alarm rate of one every five years, so still there is a chance that it could have been accidental. </p>
<p>Other signals are much stronger. For the three strongest signals detected so far you would have to wait from 1,000 times to 10 billion billion times the age of the universe for the signals to occur by chance.</p>
<h2>Knowing what to listen out for</h2>
<p>The detection of gravitational waves is a bit like acoustic ornithology.</p>
<p>Imagine you study birds and want to determine the population of birds in a forest. You know the calls of the various bird species. </p>
<p>When a bird call matches your predetermined call, you jump with excitement. Its loudness tells you how far away it is. If it was very faint against the background noise, you may be uncertain.</p>
<p>But you need to consider the <a href="https://wildambience.com/wildlife-sounds/superb-lyrebird/">lyre birds</a> that mimic other species. How do you know that sound of a kookaburra isn’t actually made by a lyre bird? You have to be very rigorous before you can claim there is a kookaburra in the forest. Even then you will only be able to be confident if you make further detections.</p>
<p>In gravitational waves we use memorised sounds called templates. There is one unique sound for the merger of each possible combination of black hole masses and spins. Each template is worked out using Einstein’s theory of gravitational wave emission.</p>
<p>In the hunt for gravitational waves, we are searching for these rare sounds using <a href="https://www.ligo.caltech.edu/page/facilities">two LIGO detectors</a> in the US and a third detector, <a href="http://public.virgo-gw.eu/language/en/">Virgo</a>, in Italy.</p>
<p>To avoid missing signals or claiming false positives, the utmost rigour is needed to analyse the data. Huge teams look over the data, search for flaws, criticise each other, review computer codes and finally review proposed publications for accuracy. Separate teams use different methods of analysis, and finally compare results.</p>
<p>Next comes reproducibility – the same result recorded again and again. Reproducibility is a critical component of science.</p>
<h2>The signals detected</h2>
<p>Before LIGO made its first public announcement of gravitational waves, two more signals had been detected, each of them picked up in two detectors. This increased our confidence and told us that there is a population of colliding black holes out there, not just a single event that could be something spurious.</p>
<p>The <a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">first detected gravitational wave</a> was astonishingly loud and it matched a pre-determined template. It was so good that LIGO spent many weeks trying to work out if it was possible for it to have been a prank, deliberately injected by a hacker. </p>
<p>While LIGO scientists eventually convinced themselves that the event was real, further discoveries greatly increased our confidence. In August 2017 a signal was detected by the two LIGO detectors and the Virgo detector in Italy.</p>
<p>On August 17 last year a completely different, but long predicted type of signal was observed from a <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">coalescing pair of neutron stars</a>, accompanied by the predicted burst of gamma rays and light.</p>
<h2>The black hole mergers</h2>
<p>Now the LIGO-Virgo collaboration has completed the analysis of all the data since September 2015. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/gmmD72cFOU4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The ten black hole mergers.</span></figcaption>
</figure>
<p>For each signal we determine the mass of the two colliding black holes, the mass of the new black hole that they create, and rather roughly, the distance and the direction. </p>
<p>Each signal has been seen in two or three detectors almost simultaneously (they were separated by milliseconds).</p>
<p>Eight of the 20 initial black holes have masses between 30 and 40 Suns, six are in the 20s, three are in the teens and only two are as low as 7 to 8 Suns. Only one is near 50, the biggest pre-collision black hole yet seen.</p>
<p>These are the numbers that will help us work out where all these black holes were made, how they were made, and how many are out there. To answer these big questions we need many more signals.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=393&fit=crop&dpr=1 600w, https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=393&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=393&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=494&fit=crop&dpr=1 754w, https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=494&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/248359/original/file-20181203-194950-77hdrk.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=494&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Graphic showing the masses of recently announced gravitational-wave detections and black holes and neutron stars.</span>
<span class="attribution"><span class="source">LIGO-Virgo / Frank Elavsky / Northwestern</span></span>
</figcaption>
</figure>
<p>The weakest of the new signals, GW170729, was detected on July 29, 2017. It was the collision of a black hole 50 times the mass of the Sun, with another 34 times the mass of the Sun.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-why-you-can-hear-gravitational-waves-when-things-collide-in-the-universe-92356">Explainer: why you can hear gravitational waves when things collide in the universe</a>
</strong>
</em>
</p>
<hr>
<p>This was by far the most distant event, having taken place, most likely, 5 billion years ago – before the birth of Earth and the Solar system 4.6 billion years ago. Despite the weak signal, it was the most powerful gravitational explosion discovered, so far. </p>
<p>But because the signal was weak, this is the detection with the false alarm rate of one every five years.</p>
<p>LIGO and Virgo are improving their sensitivity year by year, and will be finding many more events. </p>
<p>With planned new detectors we anticipate ten times more sensitivity. Then we expect to be detecting new signals about every five minutes.</p><img src="https://counter.theconversation.com/content/107962/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Blair receives funding from the Australian Research Council. He is affiliated with the Gravity Discovery Centre Foundation that operates an exciting self-funded education centre near Gingin, Western Australia where you can find out much more about black holes, neutron stars and gravitational waves. </span></em></p>More ripples in space-time have been detected from merging pairs of black holes, one of which was the most massive and distant gravitational-wave source ever observed.David Blair, Emeritus Professor, ARC Centre of Excellence for Gravitational Wave Discovery, OzGrav, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1038432018-09-26T20:12:36Z2018-09-26T20:12:36ZUnexpected find from a neutron star forces a rethink on radio jets<figure><img src="https://images.theconversation.com/files/237878/original/file-20180925-149967-125y575.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist’s impression of the strong magnetic field neutron star in Swift J0243.6+6124 launching a jet.</span> <span class="attribution"><span class="source">ICRAR/University of Amsterdam</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Just a little to the left of the leftmost part of the “W” in the constellation <a href="https://www.iau.org/public/themes/constellations/#cas">Cassiopeia</a> lies a binary system of a neutron star in a 27-day orbit with a more massive, rapidly rotating star.</p>
<p>It’s from here we’ve detected <a href="https://www.britannica.com/science/radio-jet">radio jets</a> – material travelling close to the speed of light and emitting radio waves – with details <a href="http://dx.doi.org/10.1038/s41586-018-0524-1">published today in Nature</a>.</p>
<p>But the find was something not predicted by current theory. This particular neutron star has a very strong magnetic field, yet jets from neutron stars had only previously been observed in systems with magnetic fields about 1,000 times weaker.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">Explainer: what is a neutron star?</a>
</strong>
</em>
</p>
<hr>
<p><a href="http://astronomy.swin.edu.au/cosmos/N/Neutron+Star">Neutron stars</a> are dense stellar corpses, with about one and a half times the mass of the Sun squeezed into a sphere just ten kilometres across.</p>
<p>With enormous densities (similar to that of an atomic nucleus), they are the densest objects that can support themselves against their own gravity. If they were any denser they would collapse to form a <a href="http://astronomy.swin.edu.au/cosmos/B/Black+Hole">black hole</a>.</p>
<h2>A Swift discovery</h2>
<p>This particular binary system, known as Swift J0243.6+6124, was first discovered on October 3, 2017, by NASA’s <a href="https://swift.gsfc.nasa.gov/">Neil Gehrels Swift Observatory</a>. This satellite, known as Swift, continuously scans the sky looking for new, bright sources of X-ray emission. </p>
<p>After a bright new burst of X-rays was detected from the location of this binary system, astronomers from across the world trained their telescopes on the source to try to determine what was producing them.</p>
<p>It turned out that the strong gravity of the neutron star in this system was capturing material thrown off by the rapid rotation of the other star. For many years this gas had been piling up in a disk of matter swirling around the neutron star.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/237879/original/file-20180925-149982-732e1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/237879/original/file-20180925-149982-732e1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/237879/original/file-20180925-149982-732e1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/237879/original/file-20180925-149982-732e1l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/237879/original/file-20180925-149982-732e1l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/237879/original/file-20180925-149982-732e1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/237879/original/file-20180925-149982-732e1l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/237879/original/file-20180925-149982-732e1l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An artist’s impression of the binary system Swift J0243.6+6124 with a neutron star in a 27-day orbit and a more massive, rapidly-rotating donor star.</span>
<span class="attribution"><span class="source">ICRAR/University of Amsterdam</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>When enough matter had accumulated, it all started to move inwards at once. We’re all familiar with a weight thrown from the top of a hill picking up speed as it falls. The physics behind this everyday phenomenon is the release of gravitational energy, which is converted into the energy of motion.</p>
<p>In exactly the same way, the gravitational energy of the mass was released as it fell in towards the neutron star. That energy was initially converted into motion, and eventually into X-ray radiation, which was what the Swift satellite detected.</p>
<h2>Closer inspection</h2>
<p>Our team, led by PhD student Jakob van den Eijnden from the University of Amsterdam, also detected radio waves from the source, using the Karl G Jansky <a href="https://public.nrao.edu/telescopes/vla/">Very Large Array</a> observatory, in New Mexico.</p>
<p>The brightness of the radio emission tracked the brightness of the X-rays from the source as the burst rose and then faded away over a period of a few months. The behaviour of the radio emission led us to conclude that it was coming from jets.</p>
<p><a href="http://astronomy.swin.edu.au/cosmos/J/Jets">Jets</a> are narrowly-focused beams of matter and energy that travel outwards at close to the speed of light. They carry away some of the gravitational energy released when matter falls in towards a central object, such as a black hole or neutron star.</p>
<p>The jets deposit this energy into the surroundings, often at very large distances from the launch point.</p>
<p>In neutron stars and black holes that are only a few times more massive than the Sun, this energy can be transported many light years away. For supermassive black holes that lie at the centres of galaxies, the jets can carry away energy to hundreds of thousands of light years from the galaxy centre.</p>
<p>The first jet was discovered 100 years ago by the <a href="https://apod.nasa.gov/debate/1920/curtis_obit.html">astronomer Heber Curtis</a>, who noticed a “curious straight ray” associated with the nearby galaxy M87. Since the dawn of radio and X-ray astronomy in the middle of last century, jets have been studied extensively.</p>
<p>They are produced whenever matter falls onto a dense central object, from newly-forming stars to white dwarfs, neutron stars and black holes. The one exception had been neutron stars with strong magnetic fields - around a trillion times stronger than that of the Sun.</p>
<h2>Against the theory</h2>
<p>Despite decades of observations, jets had not been detected in these systems. This had led to the suggestion that strong magnetic fields prevented jets from being launched.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/kMGUxmZJLQw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Astronomers need a new theory to explain these jets.</span></figcaption>
</figure>
<p>Our detection of jets from a neutron star <em>with</em> a strong magnetic field disproved the idea that had held for the past several decades. But it requires a re-examination of our theories for how jets are produced.</p>
<p>There are two main theories explaining how jets are launched. If a magnetic field threads the <a href="http://astronomy.swin.edu.au/cosmos/E/Event+Horizon">event horizon</a> of a spinning black hole, the rotational energy of the hole can be extracted to power the jets.</p>
<p>But as neutron stars have no event horizon, their jets are instead thought to be launched from rotating magnetic fields in the inner part of the disk of gas surrounding it. Particles can be flung out along magnetic field lines in much the same way as a bead will move outward on a wire that you whirl around above your head.</p>
<p>If a neutron star’s magnetic field is sufficiently strong, it should prevent the disk of matter from getting close enough to the neutron star for this second mechanism to work. We therefore need another explanation.</p>
<p>Recent theoretical work has suggested that under certain circumstances it might be possible to launch jets from the extraction of the neutron star’s rotational energy.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/once-upon-a-time-sleeping-beauties-and-the-importance-of-storytelling-in-science-102497">Once upon a time ... 'sleeping beauties' and the importance of storytelling in science</a>
</strong>
</em>
</p>
<hr>
<p>In our case, this could have been enabled by the high rate at which matter was falling inwards. It would also explain why the jets that we saw were about 100 times weaker than seen in other neutron stars with weaker magnetic fields.</p>
<p>Whatever the explanation, our result is a great example of how science works, with theories being developed, tested against observations and revised in light of new experimental results. </p>
<p>It also provides us with a new class of sources to test how magnetic fields affect the launching of jets, helping us to understand this key feedback mechanism in the universe.</p><img src="https://counter.theconversation.com/content/103843/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Miller-Jones receives funding from the Australian Research Council, and serves on the Editorial Board of the journal New Astronomy Reviews.</span></em></p>Astronomers found something not predicted by current theory when they took a closer look at the emissions from a neutron star with a very strong magnetic field.James Miller-Jones, Associate Professor, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/970442018-08-21T10:32:47Z2018-08-21T10:32:47ZSwift’s telescope reveals birth, deaths and collisions of stars through 1 million snapshots in UV<figure><img src="https://images.theconversation.com/files/221208/original/file-20180531-69481-kmpc6s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Technicians prepare Swift's UVOT for vibration testing on Aug. 1, 2002, more than two years before launch, in the High Bay Clean Room at NASA's Goddard Space Flight Center in Greenbelt, Md.
</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/swift/bursts/swift-images.html">NASA's Goddard Space Flight Center </a></span></figcaption></figure><p>Imagine if the color camera had never been invented and all our images were in black and white. The world would still look beautiful, but incomplete. For thousands of years, that was how humans saw the universe. On Earth, we can only see part of the light that stars emit.</p>
<p>Much of what we can’t see – in the infrared, the ultraviolet, the X-ray and the gamma ray wavelengths – is blocked by the Earth’s atmosphere. For the most part, this is a good thing. The atmosphere traps infrared light keeping the Earth warm at night and blocks high-energy ultraviolet light, X-rays and gamma rays, keeping us safe from deadly cosmic radiation, while letting in visible portions of the spectrum of light. For astronomers, however, this has a drawback: We look at the universe with one eye shut, unable to receive all of the information the universe is sending to us.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=225&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=225&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=225&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=282&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=282&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221252/original/file-20180531-69514-1avj865.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=282&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Visible light is just a tiny part of the electromagnetic spectrum.</span>
<span class="attribution"><a class="source" href="https://imagine.gsfc.nasa.gov/Images/science/EM_spectrum_compare_level1_lg.jpg">NASA</a></span>
</figcaption>
</figure>
<p>Launched on November 20, 2004, and orbiting an altitude of 340 miles, NASA’s <a href="https://swift.gsfc.nasa.gov">Neil Gehrels Swift Observatory</a> has three telescopes that monitor the universe using wavelengths of light that are blocked by Earth’s atmosphere. These included the X-Ray Telescope, the gamma-ray-sensitive Burst-Alert Telescope and the Ultraviolet Optical Telescope (UVOT). The UVOT recently delivered its 1 millionth image – data that astrophysicists like me use to gain insights into everything from the origins of the universe to the chemical composition of nearby comets.</p>
<h2>Watching the birth of black holes</h2>
<p>Swift’s primary mission is to study the afterglow of gamma ray bursts (GRBs) – which document the birth of black holes. Black holes are forged in the most violent explosions in the universe – the explosion of a massive star or the merging of two neutron stars (the shriveled husks left over from past stellar explosions). These explosions are so powerful – producing tens to hundreds of billions of times more energy than the sun – that even though they occur billions of light years away from Earth, they can still be detected by instruments like Swift. In fact, the first GRBs were detected by the <a href="https://heasarc.gsfc.nasa.gov/docs/heasarc/missions/vela5a.html">Vela satellites</a>, which were built to detect the explosions of nuclear weapons. </p>
<p>Over nearly 14 years, Swift has studied over a thousand GRBs. In doing so, it has revealed what powers them and given us glimpses into the furthest reaches of the cosmos, to the time when the first stars were being formed after the Big Bang.</p>
<p>However, one of the things you learn working on a space telescope mission is that if you build it, they will come. The mission provides capabilities to the community of astrophysicists – simultaneous X-ray/UV imaging and a rapid response to requests to observe and photograph specific sections of the sky – which are only available to Swift. We can focus our telescopes on an object of interest within hours of a “Target of Opportunity” request through our website, something no other mission can do. UVOT also fills an important niche by observing larger areas of the sky than can be observed with the more powerful UV instruments aboard the <a href="https://www.nasa.gov/mission_pages/hubble/main/index.html">Hubble Space Telescope</a>. These capabilities have proved a boon to the community and enabled study all sorts of objects and phenomenon beyond GRBs. </p>
<h2>Swift’s ultraviolet-aided discoveries</h2>
<p>Nearby galaxies are full of activity with new stars being formed. Swift is able to capture panoramic ultraviolet images that highlight the youngest, most massive stars in these galaxies. This gives us insight into what the universe has been doing over the last few hundred million years. My research team’s work has focused on nearby galaxies – like Andromeda and the Magellanic Clouds – to reveal what processes drive their past and ongoing star formation.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=298&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=298&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=298&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=374&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=374&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221218/original/file-20180531-69514-1ojaoax.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=374&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">On the left is an image of the nearby galaxy NGC 3623 taken with UV. On the right is an optical image. Note how the galaxies spiral arms — where new stars are being born — stand out in the ultraviolet wavelengths emitted by these hot objects.</span>
<span class="attribution"><span class="source">NASA/Swift/L.McCauley, PSU</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>With UVOT, we get a much better view of supernova explosions. These can occur when a white dwarf, the remnant of a star like the sun, explodes, or during the final death throes of a massive star, more than eight times the mass of the sun. These events generate enormous amounts of ultraviolet light, and Swift has a unique ability to observe them within hours of discovery. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221213/original/file-20180531-69501-1hs7vbv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=482&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">On the left is an ultraviolet composite made from several images of the Whirpool Galaxy (M51) taken between 2005-2007. The image on the right was made in June 2011, shortly after astronomers detected the explosion of a massive star in one of the galaxy’s outer spiral arms. The object is marked by the red circle.</span>
<span class="attribution"><span class="source">NASA/Swift/E. Hoversten, PSU</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Comets sweep through our solar system, transforming from a frozen solid ball to a vapor as they approach the sun and creating magnificent tails of ionized particles. Swift studies these comets, and analyzes their chemical composition by breaking the light they emit into different wavelengths. Swift also allows scientists to measure a comet’s rotation by seeing how the light changes over time. This has revealed that violent eruptions on the comet surface can dramatically alter a comet’s path. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=541&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=541&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=541&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=680&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=680&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221217/original/file-20180531-69484-12raesi.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=680&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This image of Comet Lulin was taken by Swift on January 28, 2009. It shows data obtained by Swift’s Ultraviolet/Optical Telescope (blue and green) and X-Ray Telescope (red). The image of the star field (white) was acquired by the Digital Sky Survey. At the time of the observation, comet Lulin was 99.5 million miles from Earth and 115.3 million miles from the sun. The ultraviolet light comes from hydroxyl molecules and shows that, at this time, Lulin was shedding 800 gallons of water every second.</span>
<span class="attribution"><span class="source">D. Bodewits/Swift/NASA</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>One of the most exciting discoveries that Swift made was connected with the recent discovery of gravitational waves by the <a href="https://losc.ligo.org/detector_status/">Laser Interferometer Gravitational-Wave Observatory</a> (LIGO). Gravitational waves are distortions in the fabric of spacetime created by the motions of extremely massive objects. In August of 2017, two neutrons stars collided in a distant galaxy, creating gravitational waves powerful enough to be detected on Earth. Swift was one of an army of telescopes that looked for the source of the gravitational waves. The mad scramble over those few days led to one of the most exciting discoveries of the last decade – a luminous afterglow from the source of the gravitational waves. This has opened up new branches of science by connecting a new way of studying the universe – through gravitational waves – to the traditional way – through light.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=532&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=532&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=532&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=669&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=669&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221384/original/file-20180601-142102-2rarg4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=669&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 depiction of a space warping collision of two merging neutron stars. The ripples represent the gravitational waves that distort the space-time grid. The narrow beams shooting out of the collision show the gamma rays burst that are released after the gravitational waves. The yellow clouds glow with other wavelengths of light that are generated in the collision.</span>
<span class="attribution"><a class="source" href="https://www.ligo.caltech.edu/page/press-release-gw170817">NSF/LIGO/Sonoma State University/A. Simonnet</a></span>
</figcaption>
</figure>
<p>UVOT has been taking snapshots of the universe since 2004 and finally piled up its millionth image. Its success is a testament to the international team of engineers, scientists and staff at the three institutions that support it – the <a href="http://www.psu.edu">Pennsylvania State University</a>; <a href="http://www.ucl.ac.uk/mssl/">Mullard Space Science Laboratory</a> in Surrey, England; and NASA’s <a href="https://www.nasa.gov/goddard">Goddard Space Flight Center</a> in Greenbelt, Maryland. It has been my privilege to be a part of this team for the last nine years. What does the future hold for UVOT? We hope to find more sources of gravitational waves, survey nearby galaxies, study even more supernovae, and monitor how objects in the universe change over time.</p>
<p>Here’s to the next million images.</p><img src="https://counter.theconversation.com/content/97044/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Siegel is a Research Professor at Pennsylvania State University and receives research funding from NASA.</span></em></p>The Swift Observatory passed a milestone: 1 million snapshots of the universe. These exquisite and revealing pictures have captured the births and deaths of stars, gravitational waves and comets.Michael Siegel, Research Professor of Astronomy and Astrophysics, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1003822018-08-16T20:17:50Z2018-08-16T20:17:50ZWe’re going to get a better detector: time for upgrades in the search for gravitational waves<figure><img src="https://images.theconversation.com/files/231640/original/file-20180813-2915-1w3rsut.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's depiction of a pair of neutron stars colliding.</span> <span class="attribution"><a class="source" href="https://www.ligo.caltech.edu/WA/news/ligo20171016">NASA/Swift/Dana Berry</a></span></figcaption></figure><p>It’s been a year since <a href="https://www.ligo.caltech.edu/page/what-are-gw">ripples in space-time</a> from a <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">colliding pair of dead stars</a> tickled the gravitational wave detectors of the <a href="https://www.ligo.caltech.edu">Advanced LIGO</a> and <a href="http://public.virgo-gw.eu/language/en/">Advanced Virgo</a> facilities. </p>
<p>Soon after, astronomers around the world began a <a href="https://theconversation.com/after-the-alert-radio-eyes-hunt-the-source-of-the-gravitational-waves-85106">campaign</a> to observe the <a href="https://theconversation.com/we-beat-a-cyber-attack-to-see-the-kilonova-glow-from-a-collapsing-pair-of-neutron-stars-85660">afterglow</a> of the collision of a binary <a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">neutron star</a> merger in radio waves, microwaves, visible light, x-rays and more.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">Explainer: what is a neutron star?</a>
</strong>
</em>
</p>
<hr>
<p>This was the dawn of <a href="https://arxiv.org/abs/1606.09335">multi-messenger astronomy</a>: a new era in astronomy, where events in the universe are observed with more than just a single type of radiation. In this case, the messengers were gravitational waves and electromagnetic radiation. </p>
<h2>What we’ve learned (so far)</h2>
<p>From this single event, we learned an incredible amount. Last October, on the day the detection was made public, 84 scientific papers were published (or the preprints made available). </p>
<p>We learned that <a href="http://iopscience.iop.org/article/10.3847/2041-8213/aa920c">gravity and light travel at the same speed, neutron star mergers are a source of short gamma-ray bursts</a>, and that kilonovae – the explosion from a neutron star merger – are <a href="https://theconversation.com/cosmic-alchemy-colliding-neutron-stars-show-us-how-the-universe-creates-gold-86104">where our gold comes from</a>. </p>
<p>This rich science came from the fact that we were able to combine our observatories to witness this single event from multiple astronomical “windows”. The gravitational waves arrived first, followed 1.7 seconds later by gamma-rays. That is a pretty small delay, considering the waves had been travelling for 130 million years. </p>
<p>Over the next few weeks, visible light and radio waves began to be observed and then <a href="https://theconversation.com/signals-from-a-spectacular-neutron-star-merger-that-made-gravitational-waves-are-slowly-fading-away-94294">slowly faded</a>. </p>
<p>It seemed like the news about gravitational waves was coming fast and furious, with the <a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">first detection announced in 2016</a>, a <a href="https://theconversation.com/an-award-with-real-gravity-how-gravitational-waves-attracted-a-nobel-prize-66491">Nobel prize in 2017</a>, and the announcement of the binary neutron star merger just weeks after the Nobel prize.</p>
<h2>Time for upgrades</h2>
<p>On this first anniversary of the neutron star merger, the gravitational wave detectors are offline for upgrades. They actually went offline shortly after the detection and will come back online some time early in 2019. </p>
<p>The work of making gravitational wave detectors function requires extraordinary patience and dedication. These are exquisite experiments – it took more than 40 years of technological development by a community of more than a thousand scientists to get to the point of detecting the first signal.</p>
<p>Naturally, improving on this work is not easy. So what does it actually take?</p>
<p>We really do <a href="https://theconversation.com/explainer-why-you-can-hear-gravitational-waves-when-things-collide-in-the-universe-92356">listen to gravitational waves</a>, and our detectors act more like microphones than telescopes or cameras. </p>
<p>If you listen to the first ever gravitational wave signal (below) you can hear the wave-chirp itself, accompanied by a rumbling hiss (the audio is shifted to a higher frequency to make it easier to hear). </p>
<p><audio preload="metadata" controls="controls" data-duration="4" data-image="" data-title="The first gravitational wave signal." data-size="23222" data-source="LIGO Open Science Center" data-source-url="" data-license="" data-license-url="">
<source src="https://cdn.theconversation.com/audio/1251/gw150914-h1-shifted.m4a" type="audio/mp4">
</audio>
<div class="audio-player-caption">
The first gravitational wave signal.
<span class="attribution"><span class="source">LIGO Open Science Center</span><span class="download"><span>22.7 KB</span> <a target="_blank" href="https://cdn.theconversation.com/audio/1251/gw150914-h1-shifted.m4a">(download)</a></span></span>
</div></p>
<p>That hiss is noise in our detector. It’s what limits our ability to find gravitational waves, and it also limits our ability to infer properties about their sources. </p>
<p>It’s a bit like if you’re standing in the kitchen and you want listen to birds singing outside, but you can’t really hear them because the dishwasher is running too loudly. </p>
<h2>Quiet please!</h2>
<p>To detect gravitational waves, we need to do more than just turn off the dishwasher. We need to build the quietest, <a href="https://arxiv.org/abs/1604.00439">best-isolated thing on Earth</a>. </p>
<p>If we could eliminate the noise in our detectors entirely, the gravitational wave chirp would sound like this (again, the audio is shifted to a higher frequency to make it easier to hear): </p>
<p><audio preload="metadata" controls="controls" data-duration="0" data-image="" data-title="A theoretical, noiseless version of the first gravitational wave signal (GW150914)." data-size="6072" data-source="" data-source-url="" data-license="" data-license-url="">
<source src="https://cdn.theconversation.com/audio/1252/gw150914-nr-shifted.m4a" type="audio/mp4">
</audio>
<div class="audio-player-caption">
A theoretical, noiseless version of the first gravitational wave signal (GW150914).
</div></p>
<p>Unfortunately, the laws of quantum mechanics and thermodynamics both prevent us from eliminating the noise entirely. Nonetheless, we strive to do the best that these fundamental limits permit. This involves, among many other extraordinary things, <a href="https://www.ligo.caltech.edu/mit/video/ligo20170216v">hanging our mirrors on glass threads</a> . </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/230163/original/file-20180801-136676-q10d0r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Before sealing up the chamber and pumping the vacuum system down, a LIGO optics technician inspects one of LIGO’s core optics (mirrors) by illuminating its surface with light at a glancing angle.</span>
<span class="attribution"><span class="source">Matt Heintze/Caltech/MIT/LIGO Lab</span></span>
</figcaption>
</figure>
<p>Our mirrors weight 40kg each and are suspended from four of these glass threads, which are less than a half-millimetre in diameter and exquisitely crafted.</p>
<p>The threads are under enormous stress, and the slightest imperfection (or the slightest touch) can cause them to explode.</p>
<p>Just such an explosion happened earlier this year while installing a new mirror. Fortunately, the precious mirror fell into a cradle designed for just such a possibility, and was not damaged. </p>
<p>Nonetheless, the delicate, intricate work of creating the glass threads, attaching them to the mirror, hanging the mirror and then installing it all needed to be redone. </p>
<h2>Improvements to the detector</h2>
<p>This was a heartbreaking setback for the team, but the added delay was not entirely in vain. In parallel with remaking the glass threads and rehanging the new mirror, we made some other improvements to the detector, for which we otherwise would not have had enough time. </p>
<p>One of the goals of this upgrade period is to install something called a quantum squeezed light source into the gravitational wave detectors.</p>
<p>As mentioned earlier, quantum mechanics mandates a certain minimum amount of noise in any measurement. We can’t arbitrarily reduce this quantum noise, but we can move it around and change its shape by <em>squeezing</em> it.</p>
<p>This is a bit like sweeping dust under the rug. It’s not really gone, but it might not bother you so much anymore. The quantum squeezed light source does just this. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=258&fit=crop&dpr=1 600w, https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=258&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=258&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=324&fit=crop&dpr=1 754w, https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=324&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/230186/original/file-20180801-136661-le9s6v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=324&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Australian National University scientists Nutsinee Kijbunchoo and Terry McCrae build components for a quantum squeezed light source at LIGO Hanford Observatory in Washington, US.</span>
<span class="attribution"><span class="source">Nutsinee Kijbunchoo</span></span>
</figcaption>
</figure>
<p>A gravitational wave detector is already a very complex system, and a squeezed light source is another complex system, so putting them together can be a challenge. </p>
<p>Despite the complexity of this challenge, when the squeezed light source was activated for the first time at the LIGO detector in Livingston, Louisiana, US, in February this year there was an immediate improvement in the quantum noise: the gravitational wave detector output got just a bit quieter.</p>
<hr>
<p>
<em>
<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>
</strong>
</em>
</p>
<hr>
<p>Much tuning remains to be done to get the detectors in optimal shape, but it is a real delight when something so complex goes well right from the start. </p>
<p>With these first detections, we have begun to explore the population of black holes in the universe, heard the merger of neutron stars, and
<a href="https://arxiv.org/abs/1712.03240">probably witnessed the birth of a new black hole</a>. </p>
<p>With the upgrades under way, we will study these objects with better clarity, hopefully understand where they came from, and maybe even find something completely new and unexpected.</p><img src="https://counter.theconversation.com/content/100382/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robert Ward receives funding from the Australian Research Council. </span></em></p>To better detect gravitational waves, we need to build the quietest and most isolated thing on Earth. And make sure we don’t drop those 40kg mirrors.Robert Ward, Associate Investigator, OzGrav (ARC Centre of Excellence for Gravitational Wave Discovery), Research Fellow in Physics, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/991682018-07-04T17:02:09Z2018-07-04T17:02:09ZFree-falling dead stars show that a cornerstone of physics holds up<figure><img src="https://images.theconversation.com/files/226123/original/file-20180704-73300-r9wjec.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Triple star system involving a pulsar suggests Einstein was right.</span> <span class="attribution"><span class="source">Kevin Gill/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>It may not be intuitive, but drop a hammer and a feather and – in the absence of air resistance – they will hit the ground at exactly the same time. This is a key principle of physics known as “universal free fall”, stating that all objects accelerate identically in the same gravitational field. In fact, it’s an important theme in Albert Einstein’s <a href="https://theconversation.com/how-einsteins-general-theory-of-relativity-killed-off-common-sense-physics-50042">immensely successful theory</a> of general relativity, which describes how gravity works. </p>
<p>But although we know it holds true for hammers and feathers, it’s been unclear whether the principle extends to extreme objects such as stars. Now a new study, <a href="https://www.nature.com/articles/s41586-018-0265-1">published in Nature</a>, has tested the principle using a remarkably extreme astrophysical environment: a <a href="https://en.wikipedia.org/wiki/PSR_J0337%2B1715">triple star system</a> containing two <a href="https://en.wikipedia.org/wiki/White_dwarf">white dwarfs</a> and a <a href="https://en.wikipedia.org/wiki/Pulsar">pulsar</a> (a rotating <a href="https://en.wikipedia.org/wiki/Neutron_star">neutron star</a> that beams radio waves). These objects are the extremely dense remnants of dead stars.</p>
<p>Spoiler alert: It turns out Einstein is still right, and it is getting even harder to prove him wrong.</p>
<p>But let’s start with the basics. Hold an object in your hand. It doesn’t matter what it is – the object will have some mass. We can think of that mass in two ways. Isaac Newton <a href="https://www.grc.nasa.gov/www/K-12/airplane/newton.html">taught us</a> that if we apply a force to a body it will undergo an acceleration, and the size of that acceleration is directly proportional to the amount of force applied – and inversely proportional to the mass itself. Give a broken-down car a push and it won’t accelerate very quickly, but apply that same push to a shopping trolley and you’ll send it careering down the aisle. When thinking about the acceleration of an object due to a force exerted on it, we think about the “<a href="https://www.britannica.com/science/inertial-mass">inertial mass</a>” of the body. </p>
<p>Any two objects with mass are attracted to each other through the gravitational force. So the object you are holding in your hand is attracted to the Earth, and the size of the force pulling it down is dependent on the mass of the object. In this case, we think about the “gravitational mass”.</p>
<p>If you dropped it, the object you are holding would “free fall” – the force of gravity would accelerate it towards the ground. The size of the force pulling the object down depends on the gravitational mass, but the amount of acceleration depends on the inertial mass. But is there any difference between the two types of mass? To find out, we can write down an equation of motion linking the two types of mass: inertial mass on one side of the equation and gravitational mass on the other. </p>
<p>The equation predicts something we can test using an experiment: if inertial mass is equivalent to gravitational mass, then all objects should fall towards the Earth with an identical acceleration <em>regardless</em> of their mass. That often surprises people. This is called the “Equivalence Principle”.</p>
<p>Galileo first noticed that plummeting objects <a href="https://science.nasa.gov/science-news/science-at-nasa/2007/18may_equivalenceprinciple">fall at the same rate</a>, and you can do this experiment yourself by simultaneously dropping two objects of different mass. However one problem doing this on Earth is the presence of another force acting on the falling bodies, called air resistance. If you drop a hammer and a feather, the feather will tend to gently drift down to the ground, lagging behind – the objects aren’t strictly in free fall. But go to the moon and do that experiment, as astronaut David Scott did during <a href="https://www.nasa.gov/mission_pages/apollo/missions/apollo15.html">Apollo 15</a>, where there is no air resistance, and the Equivalence Principle is clear to see.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/KDp1tiUsZw8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Now, it has been unclear whether the theory does a good job of describing gravity in <em>all</em> situations. There is a lot at stake – if general relativity breaks down for certain situations then we would need a revised or modified theory of gravity. In particular, scientists have been wondering whether the universality of free fall applies to objects that have strong “self gravity” – a significant gravitational field of their own. Indeed some <a href="https://en.wikipedia.org/wiki/Alternatives_to_general_relativity">modified theories of gravity</a> predict that the Equivalence Principle might be violated for strongly self-gravitating bodies in free fall, whereas general relativity says it should be universal. </p>
<h2>Dance of stars</h2>
<p>Thanks to an extreme laboratory in space – a triple stellar system <a href="https://en.wikipedia.org/wiki/PSR_J0337%2B1715">4,200 light years away</a> – the new study managed to test this. That name doesn’t do it justice: we’re talking about two white dwarfs and a more massive “millisecond” pulsar (a neutron star rotating about 366 times a second, and beaming radio waves like a lighthouse). One white dwarf and the pulsar are orbiting each other every 1.6 days. In turn they also orbit around the other white dwarf every 327 days.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/226147/original/file-20180704-73332-15vygwe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/226147/original/file-20180704-73332-15vygwe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/226147/original/file-20180704-73332-15vygwe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/226147/original/file-20180704-73332-15vygwe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/226147/original/file-20180704-73332-15vygwe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/226147/original/file-20180704-73332-15vygwe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/226147/original/file-20180704-73332-15vygwe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A triple stellar system involving normal stars, similar to the sun.</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>The pulsar-white dwarf pair can be considered to be in free fall towards the other white dwarf, because an orbit is just the case of free fall without ever reaching the ground, like satellites around the Earth. Of course, the pulsar and white dwarf are very massive objects themselves, with strong self gravity. General relativity predicts that the accelerations of the white dwarf and pulsar, due to being in free fall towards the outer white dwarf, should be identical – despite differences in mass and self-gravity.</p>
<p>Combining observations that span six years of monitoring, the astrophysicists carefully modelled the orbits of the pair. They measured a parameter called Delta, which describes the fractional difference between the acceleration of the white dwarf and the more massive pulsar. If general relativity holds, then Delta should be equal to zero. The results indicate that, within the uncertainties of the measurements, the difference in accelerations is indeed statistically consistent with zero – we can say with 95% confidence that Delta is less than 0.0000026.</p>
<p>This new constraint is far better than anything previously measured. It provides valuable new empirical evidence that general relativity remains our best model of how gravity works, so we are unlikely to need any new or modified theories at this point. This come just weeks after general relativity <a href="https://theconversation.com/how-we-proved-einstein-right-on-a-galactic-scale-and-what-it-means-for-dark-energy-and-dark-matter-98481">was proven right on a galactic scale</a> for the first time.</p>
<p>Will we ever find a situation where general relativity breaks down? In a way I do hope so, because it would reveal new physics. But the continuing success of general relativity, first written down a century ago, must surely be celebrated as one of the most incredible intellectual achievements of our species.</p><img src="https://counter.theconversation.com/content/99168/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Geach receives funding from the Royal Society. </span></em></p>An extreme laboratory in space involving three dead stars has shown that all objects really do accelerate identically, proving Einstein right.James Geach, Royal Society University Research Fellow, University of HertfordshireLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/942942018-04-30T20:15:47Z2018-04-30T20:15:47ZSignals from a spectacular neutron star merger that made gravitational waves are slowly fading away<figure><img src="https://images.theconversation.com/files/215476/original/file-20180418-134691-1ijq629.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Neutron star merger.</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/12740">Credit: NASA's Goddard Space Flight Center/CI Lab</a></span></figcaption></figure><p>Eight months ago, the <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">detection of gravitational waves</a> from a binary neutron star merger had us and other astronomers around the world rushing to observe one of the most energetic events in the universe. </p>
<p>What most people don’t realise is that we continued to observe the event every few weeks from then up to now. </p>
<p>Our team <a href="https://theconversation.com/after-the-alert-radio-eyes-hunt-the-source-of-the-gravitational-waves-85106">started searching for radio emission from the merger</a>, <a href="https://www.ligo.caltech.edu/page/press-release-gw170817">known as GW170817</a>, making a detection two weeks after the August event. Now, the radio emission is starting to fade. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/after-the-alert-radio-eyes-hunt-the-source-of-the-gravitational-waves-85106">After the alert: radio 'eyes' hunt the source of the gravitational waves</a>
</strong>
</em>
</p>
<hr>
<p>As we prepare to say goodbye (at least for now) to this incredible object, we reflect on what what we’ve learned so far, with <a href="https://arxiv.org/abs/1803.06853" title="A turnover in the radio lightcurve of GW170817">our paper accepted for publication</a> in the Astrophysical Journal. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=429&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=429&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=429&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=539&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=539&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215472/original/file-20180418-163991-1562c4z.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=539&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Radio observations of GW170817 from two telescopes. The central bright object in each image is the host galaxy NGC 4993. The smaller bright spot in the crosshairs is the neutron star merger.</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/nature25452">David Kaplan. Data from Mooley et al. (2018), Nature, 554, 207</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The detection of gravitational waves and electromagnetic radiation (such as light and radio waves) from the same object mean physicists have been able to:</p>
<ul>
<li><p>confirm a prediction of general relativity that <a href="https://www.ligo.org/science/Publication-GW170817GRB/index.php">gravitational waves travel at the speed of light</a></p></li>
<li><p>figure out <a href="https://theconversation.com/why-astrophysicists-are-over-the-moon-about-observing-merging-neutron-stars-84957">how matter behaves when you squeeze it</a> harder than in the nucleus of an atom</p></li>
<li><p><a href="https://theconversation.com/cosmic-alchemy-colliding-neutron-stars-show-us-how-the-universe-creates-gold-86104">explain</a> where some of the gold (and other heavy elements) in the universe are produced</p></li>
<li><p>and start to solve a decades-old mystery about <a href="https://theconversation.com/how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal-85647">what causes short gamma-ray bursts</a>.</p></li>
</ul>
<h2>Observing the merger</h2>
<p>Radio telescopes such as the <a href="https://www.narrabri.atnf.csiro.au/public/">Australia Telescope Compact Array</a> and the <a href="http://www.vla.nrao.edu/">Jansky Very Large Array</a> (in the United States) are designed to detect electromagnetic radiation with wavelengths from centimetres to metres.</p>
<p>Unlike visible light, radio waves travel through space almost unimpeded by dust. They can be detected during the day as well as at night: radio telescopes can observe around the clock.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/1hawK5JwVfY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Timelapse of the CSIRO’s Australia Telescope Compact Array. Credit: Alex Cherney (terrastro.com)</span></figcaption>
</figure>
<p>The radio waves we detected have travelled 130 million light years from the galaxy <a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=NGC+4993">NGC 4993</a> where the neutron star merger took place. </p>
<p>When the two neutron stars collided they emitted a burst of gamma rays shortly after, which was detected by the Fermi satellite 1.74 seconds after the gravitational waves. What happened next in the explosion is what we’ve all been trying to work out.</p>
<p>Within 12 hours astronomers had detected a bright, fading signal in visible light. We think this came from neutron star material flung out at 50% of the speed of light. It was glowing hot from a bunch of radioactive decays. </p>
<p><a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">Neutron stars</a> are the most dense objects we know of, except for black holes: imagine the Sun squashed into a region the size of a city. </p>
<p>When two neutron stars collide they form a new object that has slightly less mass than the two original stars: in this case likely a new black hole. A tiny fraction of the mass is blasted out as both matter and energy (remember E=mc<sup>2)</sup> and that is what we detect on Earth.</p>
<h2>What do radio waves tell us?</h2>
<p>The radio emission we detected days later, though, is a different matter.</p>
<p>Radio waves are created when electrons are accelerated in magnetic fields. This happens at shock fronts in space, as material from stellar explosions crashes into the stuff around the star. </p>
<p>This stuff is called the interstellar medium and is about 10 quintillion times less dense than air on Earth (almost, but not quite, a vacuum). The nature of the radio waves tells us the details of this shock, which we can run backward in time to try to understand the explosion. </p>
<p>One big question is whether there was a narrow jet of material moving at 99.99% of the speed of light that punched its way out of the explosion and hit the interstellar medium.</p>
<p>We think that these must happen in gamma-ray bursts: did that happen here? </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/p2Ab26gnQ1g?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A simulation of a neutron-star merger giving rise to a broad outflow – a ‘cocoon’. A cocoon is the best explanation for the radio waves, gamma rays and X-rays the astronomers saw arising from the neutron-star merger GW170817.</span></figcaption>
</figure>
<h2>What happened in the explosion?</h2>
<p>We’re still not sure of the details, but we don’t think there was a successful jet in GW170817. That’s because we have now observed the radio emission start to fade (the optical emission started to fade immediately).</p>
<p>This shows the explosion probably isn’t a classic gamma-ray burst with relativistic jets, as shown in the figure below (left). What is more likely is that we are seeing a “cocoon” of material that has broken out from the explosion. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=364&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=364&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=364&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=457&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=457&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215103/original/file-20180416-47416-1xf1m8z.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=457&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Models of what might be happening in the merger. Our data has shown the left option is unlikely, and the radio emission is probably caused by a cocoon of material (right).</span>
<span class="attribution"><a class="source" href="http://science.sciencemag.org/content/358/6370/1559">Reprinted with permission from Kasliwal et al., Science (2017)</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>So where does this material come from?</p>
<p>The material flung out of the neutron stars (known as ejecta) was moving fast, about 50% of the speed of light. What if there was an even faster (99.99% of the speed of light) jet that happened soon after?</p>
<p>This jet could have blown a bubble in the ejecta, making it move faster (maybe 90% of the speed of light) and stopping the jet in its tracks: we call this a cocoon.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215473/original/file-20180418-163986-k3k95p.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Radio observations of the neutron star merger show that it is now fading.</span>
<span class="attribution"><a class="source" href="https://arxiv.org/abs/1803.06853">David Kaplan, Dougal Dobie. Data from Dobie et al. (2018), ApJL</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Saying goodbye (for now)</h2>
<p>After eight months of watching GW170817 we know that it is different to anything we’ve seen before, and has behaved in completed unexpected ways.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/captured-radio-telescope-records-a-rare-glitch-in-a-pulsars-regular-pulsing-beat-94815">Captured! Radio telescope records a rare 'glitch' in a pulsar's regular pulsing beat</a>
</strong>
</em>
</p>
<hr>
<p>The radio emission is now fading, but this may not be the end of the story. Most models predict a long term afterglow from neutron star mergers, so GW170817 might reappear months or even years in the future.</p>
<p>In the meantime, we are waiting with anticipation for the <a href="https://www.ligo.caltech.edu/">Laser Interferometer Gravitational-Wave Observatory (LIGO)</a> to start its next observing run early next year. We might even capture a new type of event, a neutron star merging with a black hole.</p><img src="https://counter.theconversation.com/content/94294/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tara Murphy works for the University of Sydney. She receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>David Kaplan works for the University of Wisconsin-Milwaukee, and he receives funding from the US National Science Foundation.</span></em></p>Astronomers are getting ready to say good bye to the radio emission from a neutron star merger – one of the most energetic events in the universe – that was detected last year.Tara Murphy, Associate Professor and ARC Future Fellow, University of SydneyDavid Kaplan, Associate professor of Physics, University of Wisconsin-MilwaukeeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/948152018-04-11T20:06:51Z2018-04-11T20:06:51ZCaptured! Radio telescope records a rare ‘glitch’ in a pulsar’s regular pulsing beat<figure><img src="https://images.theconversation.com/files/214213/original/file-20180411-560-1dkl4zt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Vela pulsar makes about 11 complete rotations every second, it also has a glitch.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/chandra/multimedia/vela2012.html">X-ray: NASA/CXC/Univ of Toronto/M.Durant et al; Optical: DSS/Davide De Martin</a></span></figcaption></figure><p>Pulsars are rapidly rotating neutron stars and sometimes they abruptly increase their rotation rate. This sudden change of spin rate is called a “glitch” and I was part of a team that recorded one happening in the Vela Pulsar, with the results <a href="http://nature.com/articles/doi:10.1038/s41586-018-0001-x">published today in Nature</a>.</p>
<p>Approximately 5-6% of pulsars are known to glitch. The Vela pulsar is perhaps the most famous – a very southern object that spins about 11.2 times per second and was discovered by scientists in Australia in 1968.</p>
<p>It is 1,000 light-years away, its supernova occurred about 11,000 years ago and roughly once every three years this pulsar suddenly speeds up in rotation.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/fifty-years-ago-jocelyn-bell-discovered-pulsars-and-changed-our-view-of-the-universe-88083">Fifty years ago Jocelyn Bell discovered pulsars and changed our view of the universe</a>
</strong>
</em>
</p>
<hr>
<p>These glitches are unpredictable, and one has never been observed with a radio telescope large enough to see individual pulses.</p>
<p>To understand what the glitch may be, first we need to understand what makes a pulsar.</p>
<h2>Collapsing stars</h2>
<p>At the end of a typical star’s life, one of three things can happen.</p>
<p>A small star, similar to the size of our Sun, will just quietly expire like a fire going out. </p>
<p>If the star is sufficiently large, a supernova will occur. After this massive explosion the remains will collapse. If the object is sufficiently large then its escape velocity will be greater than the speed of light, and a <a href="http://astronomy.swin.edu.au/cosmos/B/Black+Hole">black hole</a> will be formed.</p>
<p>But if we have a Goldilocks-sized star that is large enough to go <a href="http://astronomy.swin.edu.au/cosmos/S/Supernova">supernova</a>, but small enough not to be a black hole, we get a <a href="http://astronomy.swin.edu.au/cosmos/N/Neutron+Star">neutron star</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-why-you-can-hear-gravitational-waves-when-things-collide-in-the-universe-92356">Explainer: why you can hear gravitational waves when things collide in the universe</a>
</strong>
</em>
</p>
<hr>
<p>The gravity is so strong that the electrons orbiting the atom are forced into the nucleus. They combine with protons in the nucleus to form neutrons.</p>
<p>These objects are estimated to have a mass of about 1.4 times the mass of our Sun, and a diameter of 20km. The density is such that a cupful of this material would weigh as much as Mt Everest.</p>
<p>They also rotate quite quickly (and very gradually slow down over time) as well as having a massive magnetic field, three trillion times that of the Earth. Electromagnetic radiation emits from both ends of this huge rotating magnet. </p>
<p>Now if one of the poles of this rotating magnet happens to sweep past Earth, we see a brief “flash” in radio waves (and other frequencies too) once every rotation. This is called a <a href="http://astronomy.swin.edu.au/cosmos/P/Pulsar">pulsar</a>.</p>
<h2>The hunt for a ‘glitch’</h2>
<p>In 2014 I started a serious observing campaign with the University of Tasmania’s 26m radio telescope, at the <a href="http://www.utas.edu.au/maths-physics/facilities/mt-pleasant-observatory">Mount Pleasant Observatory</a>, with a goal to catch the Vela Pulsar’s glitch live in action.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The 26m antenna at the Mount Pleasant Radio Observatory.</span>
<span class="attribution"><span class="source">University of Tasmania</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>I collected data at the rate of 640MB for each 10 second file, for 19 hours a day, for most days over nearly four years. This resulted in over 3PB of data (1 petabyte is a million gigabytes) that was collected, processed and analysed.</p>
<p>On December 12, 2016, at approximately 9:36pm at night, my phone goes off with a text message telling me that Vela had glitched. The automated process I had set up wasn’t completely reliable – radio frequency interference (RFI) had been known to set it off in error. </p>
<p>So sceptically I logged in, and ran the test again. It was genuine! The excitement was incredible and I stayed up all night analysing the data.</p>
<p>What surfaced was quite surprising and not what was expected. Right as the glitch occurred, the pulsar missed a beat. It didn’t pulse. </p>
<p>The pulse before this “null” was broad and weird. Nothing like I’d ever seen or heard of before.</p>
<p>The two pulses following turned out to have no linear polarisation which was also unheard of for Vela. This meant the glitch had affected the strong magnet that drives the emission that comes from the pulsar.</p>
<p>Following the null, a train of 21 pulses arrived early and the variance in their timings was a lot smaller than normal – also very weird.</p>
<h2>The glitch explained, sort of</h2>
<p>So what causes glitches? The hypothesis that is best supported is that the neutron star has a hard crust and a superfluid core. The outer crust is what slows down, while the superfluid core rotates separately and does not slow down.</p>
<p>This is a very simplified explanation. What really happens is quite complex and involves microscopic superfluid vortices unpinning from the crust’s lattice.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/stars-for-sale-but-no-you-cant-really-buy-an-official-star-name-to-remember-someone-92033">Stars for sale, but no, you can't really buy an official star name to remember someone</a>
</strong>
</em>
</p>
<hr>
<p>After about three years the difference in rotation between the core and crust gets too great and the core “grips” the crust and speeds it up. The data seems to show that it took about five seconds for this speed-up to occur. This is on the faster end of the scale that the theorists had predicted. </p>
<p>All this and other information could help us understand what is called the “equation of state” – how matter behaves at different temperatures and pressures – in a laboratory that we simply cannot create here on Earth.</p>
<p>It also gives us, for the first time, a glimpse into the inside workings of a neutron star.</p><img src="https://counter.theconversation.com/content/94815/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jim Palfreyman received funding from the Australian Government Research Training Program Scholarship, which helped fund this research. </span></em></p>Pulsars are rapidly rotating neutron stars and some of them are know to have a “glitch”, and astronomers have captured one as it hapened.Jim Palfreyman, PhD candidate in astronomy, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/923562018-03-12T19:05:48Z2018-03-12T19:05:48ZExplainer: why you can hear gravitational waves when things collide in the universe<figure><img src="https://images.theconversation.com/files/209273/original/file-20180307-146675-1ki0syv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">ns gw art</span> </figcaption></figure><p>Whenever there’s an announcement of a new discovery of gravitational waves there is usually an accompanying sound, such as this:</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/TWqhUANNFXw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The sound of first gravitational waves detected.</span></figcaption>
</figure>
<p>We have only detected half a dozen signals so far. The first five are black holes whose chirp signal is extremely brief. The last one is the sound of <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">a pair of neutron stars</a> spiralling together. This signal lasted more than a minute.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/WoDCPTLgxh4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Listen for the chirp.</span></figcaption>
</figure>
<p>With good earphones (and good ears) you may be able to hear the lower frequencies but the final chirp is unmistakable. A friend commented that the sound is like the call of the Australian whip bird.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">At last, we've found gravitational waves from a collapsing pair of neutron stars</a>
</strong>
</em>
</p>
<hr>
<p>So what is this sound? Are we really <em>hearing</em> gravitational waves?</p>
<p>To answer that it helps to think about other devices that detect waves, such as seismometers.</p>
<h2>Listening for an earthquake</h2>
<p>Today a worldwide network of seismometers listens to the Earth as it continuously vibrates. You can hear some <a href="https://earthquake.usgs.gov/learn/topics/listen/allsounds.php">examples of earthquakes online at the US Geological Survey</a> (USGS).</p>
<p><audio preload="metadata" controls="controls" data-duration="9" data-image="" data-title="The 1992 Magnitude 7.3 Landers Earthquake" data-size="112478" data-source="United States Geological Survey" data-source-url="https://earthquake.usgs.gov/learn/topics/listen/allsounds.php" data-license="" data-license-url="">
<source src="https://cdn.theconversation.com/audio/1074/mtcm.mp3" type="audio/mpeg">
</audio>
<div class="audio-player-caption">
The 1992 Magnitude 7.3 Landers Earthquake.
<span class="attribution"><a class="source" rel="nofollow" href="https://earthquake.usgs.gov/learn/topics/listen/allsounds.php">United States Geological Survey</a><span class="download"><span>110 KB</span> <a target="_blank" href="https://cdn.theconversation.com/audio/1074/mtcm.mp3">(download)</a></span></span>
</div></p>
<p>Behind the idea of the <a href="https://earthquake.usgs.gov/learn/glossary/?term=seismograph">seismometer</a> is inertia: the linking of mass to space. You feel inertia when you push a car. The more massive the car, the more slowly it speeds up. Inertia resists changes in the motion of matter through space. </p>
<p>In a seismometer a large, delicately suspended mass is freed from most forces, so its inertia links it to space. In an earthquake the ground suddenly shakes. If you feel an earthquake you are feeling sudden changes in your motion through space.</p>
<p>In the seismometer the suspended mass stays still because of its inertia, but the frame of the seismometer follows the shaking Earth. From inside the seismometer it seems as if the mass has suddenly moved.</p>
<h2>Can you hear it?</h2>
<p>Sound is a wave of vibration that we normally hear passing through the air, but we can also hear under water and through solids. <a href="https://www.britannica.com/science/seismic-wave">Seismic waves</a> are waves of vibration passing through the solid Earth and this is what is picked up by modern seismometers. </p>
<p>If you were to insist that sound must be audible to us humans, then we can’t actually hear most earthquakes. This is because the vibration frequency is usually lower than the frequency threshold of human hearing.</p>
<p>But record it and speed up the playback and you can hear symphonies of seismic sounds like those you can <a href="https://earthquake.usgs.gov/learn/topics/listen/">listen to here at the USGS</a>.</p>
<p>Gravitational waves are waves of stretching and shrinking space. Like seismometers, gravitational wave detectors use the principle of inertia, but in this case the action is reversed. Space expands and shrinks and inertia causes suspended masses to follow.</p>
<p>Motions of space cannot be detected at a single location, for the same reason you cannot measure the stretching of an elastic band at a single point. But a <em>pair</em> of separated masses will become closer together if space shrinks, and further apart if space expands. Inertia makes the masses follow space, but neither mass feels a force.</p>
<p>Similarly, the expansion of space in the universe, that proved the Big Bang theory, causes all the galaxies to be moving apart without any force driving them. But gravitational waves are different in one respect: they simultaneously stretch in one direction and shrink the perpendicular direction. </p>
<p>In essence, gravitational waves vibrate the spacing between masses. The effects are tiny, so each mass must be exquisitely suspended so that it is not affected by the vibrations of the ground, and held in vacuum so that sounds in the air do not affect them.</p>
<h2>The big breakthrough</h2>
<p>It took 50 years of technology development before we had enough sensitivity to measure these waves. The masses we use are 40kg mirrors and lasers are used to measure their spacing.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/tQ_teIUb3tE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Gravitational waves cause he mirrors to move.</span></figcaption>
</figure>
<p>Albert Einstein’s theory of <a href="https://theconversation.com/au/topics/general-relativity-161">general relativity</a> tells us that space and time are elastic. Spacetime is an elastic medium that is actually a billion billion billion times stiffer than steel. </p>
<p>We are constantly moving freely through this elastic medium, but we have to apply forces using muscles or tires or rocket engines to allow us to overcome the principle of inertia, thereby <em>changing</em> our motion through space as we have to when we move around relative to other objects.</p>
<p>If a pair of black holes orbit each other they make enormous deformations in the shape of space around them, and because of space’s elasticity, this creates ripples of space that spread out like ripples on a pond.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/zLAmF0H-FTM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Watch the ripples until the black holes collide.</span></figcaption>
</figure>
<p>When the ripples pass pairs of masses, the rippling distortions of space cause the spacing between the masses to fluctuate in unison. But as an observer you simply see that the spacing between the masses is vibrating. It looks like a sound and it sounds like a sound! The only catch is that it needs to be amplified a billion times to be audible.</p>
<p>The first signal itself was detected as a vibration of the distance between mirrors four kilometres apart. They changed their spacing by about a billionth of the diameter of an atom. </p>
<p><audio preload="metadata" controls="controls" data-duration="11" data-image="" data-title="The sound of two black holes colliding." data-size="166960" data-source="LIGO" data-source-url="https://soundcloud.com/newyorktimes/the-sound-of-two-black-holes-colliding" data-license="" data-license-url="">
<source src="https://cdn.theconversation.com/audio/320/ligo-chirp-1080p.m4a" type="audio/mp4">
</audio>
<div class="audio-player-caption">
The sound of two black holes colliding.
<span class="attribution"><a class="source" rel="nofollow" href="https://soundcloud.com/newyorktimes/the-sound-of-two-black-holes-colliding">LIGO</a><span class="download"><span>163 KB</span> <a target="_blank" href="https://cdn.theconversation.com/audio/320/ligo-chirp-1080p.m4a">(download)</a></span></span>
</div></p>
<p>Sound carries a wealth of information. Think of the vast number of characteristic sounds we all know, from a dripping tap to a breaking window, from a bird call to a kettle drum. The sound describes the system. For gravitational waves we are able to make precise predictions of the differences in gravitational wave sounds from many systems. </p>
<p>The whoops and chirps we have heard are all different, because the sounds depend on the masses of the black holes, how fast they are spinning and how they are oriented relative to the Earth. Neutron stars are much less massive than the black holes we have heard so far, and this causes the pitch of the signal to rise much more slowly. </p>
<p>All the gravitational waves we have heard so far are in the audio frequency range for the human ear: we really could hear them if our ears were sensitive enough, but real signals are just too quiet.</p>
<p>In the future gravitational wave detectors in space will be able to listen to gravitational waves at much lower frequencies. These, like earthquakes, will need to be sped up for us to hear them.</p>
<p>Gravitational wave detectors are supersensitive microphones for the sounds of space. They amplify the sound, and we get to hear the sound of gravitational waves that have travelled to us from far away in the universe. The universe speaks to us.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">Gravitational waves discovered: the universe has spoken</a>
</strong>
</em>
</p>
<hr>
<h2>A better detector</h2>
<p>From the recent discoveries we can make predictions of what we might hear as we improve the detectors. As sensitivity improves you increase the range of detection and this increases the volume of the universe you can listen to by the cube of the improvement factor. </p>
<p>Every two times improvement gives eight times as many signals. In the next few years the three detectors in the world: two <a href="https://www.ligo.caltech.edu/">LIGO detectors in the US</a> and the <a href="http://public.virgo-gw.eu/language/en/">Virgo detector in Europe</a> should be detecting hundreds of black holes and neutron stars colliding every year. Two more detectors are under construction in Japan and India.</p>
<p>More detectors helps to pinpoint where signals come from, but the biggest pay off comes from increasing sensitivity. Just four-fold further improvement would expand our horizon to encompass about half of the visible universe while a ten-fold improvement would give us the whole universe. Detectors with this capability have been suggested for Australia, China, Europe and the US. </p>
<p>The legacy of Einstein, the <a href="https://theconversation.com/an-award-with-real-gravity-how-gravitational-waves-attracted-a-nobel-prize-66491">recent Nobel Prize winners</a> and the huge international team of gravitational wave physicists that made the first discoveries, will be the ability to listen to the whole universe, and to hear it running down as black holes form and grow.</p>
<p>Gravitational waves are truly a new sense for humanity. We are no longer deaf to the sounds of space. We can be pretty certain that our new-found sense will bring with it surprises and unforeseen revelations, as well as remarkable new technologies.</p><img src="https://counter.theconversation.com/content/92356/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Blair receives funding from the Australian Research Council</span></em></p>From a slow hum to a chirp or a bleep, what is that sound you hear whenever there’s a new detection of gravitational waves?David Blair, Emeritus Professor, ARC Centre of Excellence for Gravitational Wave Discovery, OzGrav, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/889982017-12-12T14:42:56Z2017-12-12T14:42:56ZHow crashing neutron stars killed off some of our best ideas about what ‘dark energy’ is<figure><img src="https://images.theconversation.com/files/198773/original/file-20171212-9386-1cdozau.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist s impression of merging neutron stars.</span> <span class="attribution"><span class="source"> Author University of Warwick/Mark Garlick</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>There was much excitement when scientists <a href="https://theconversation.com/how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal-85647">witnessed the violent collision of two ultra-dense, massive stars</a> more than 100m light years from the Earth earlier this year. Not only did they catch the resulting gravitational waves – ripples in the fabric of spacetime – they also saw a practically instantaneous flash of light. This is exciting in itself and was the first direct evidence for a merger of neutron stars.</p>
<p>But from a cosmologist’s perspective, the photo-finish of the gravitational waves and the flash of light has at a stroke demolished years of research into a completely unrelated problem: why is the expansion of the universe accelerating? </p>
<p>It turns out that space and time are actually mutable, pliable, flexible and wiggly, rather than constant, fixed or immovable. This has been known since Einstein published his theory of general relativity, which explains how gravity warps spacetime. The subtle effects that this mutability causes need to be accounted for even in the GPS that makes your sat nav and iPhone work. </p>
<p>One prediction of Einstein’s theory was that it should be possible for spacetime to have waves in it, like the surface of the sea. These would be visible if one could, for example, smash together two black holes. This prediction was <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">dramatically seen</a> in the first detection of gravitational waves by the LIGO experiment in 2015. The discovery opened up a <a href="https://theconversation.com/experiments-simultaneously-detect-gravitational-waves-and-help-open-up-a-new-era-of-astronomy-84818">whole new way to probe the cosmos</a>, and was awarded the <a href="https://theconversation.com/scientists-behind-the-discovery-of-gravitational-waves-win-the-2017-nobel-prize-for-physics-66457">Nobel Prize for physics</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=419&fit=crop&dpr=1 600w, https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=419&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=419&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=526&fit=crop&dpr=1 754w, https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=526&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/198776/original/file-20171212-9410-1s7bsh7.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=526&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Galaxy cluster SDSS – what’s pushing it apart at an accelerated rate?</span>
<span class="attribution"><span class="source">ESA, NASA, K. Sharon (Tel Aviv University) and E. Ofek (Caltech).</span></span>
</figcaption>
</figure>
<p>The new detection of gravitational waves from the merger of neutron stars also has profound implications for our understanding of the universe. However for the cosmologists it was the flash of light 1.7 seconds after the gravitational waves that was the more intriguing observation.</p>
<h2>The cosmic speed camera</h2>
<p>The 1.7 second time delay is important because it means that the gravitational waves and the light waves had been travelling at almost <em>exactly</em> the same speed. In fact these are two of the most closely matched observed speeds ever: the two only differed by one part in 10m billion. </p>
<p>To put this into context if the speed cameras on the road could measure speed differences this finely you would get a ticket for going 30.0000000000000001mph in a 30mph zone. </p>
<p>Compared to the best measurements cosmologists were hoping for in the future this is a factor of a million billion times better. Factoring in that the electromagnetic waves may have taken a bit of time to escape from the turmoil of a neutron star collision, for all intents and purposes the speed difference is zero. </p>
<p>Cosmology is <a href="https://theconversation.com/cosmology-is-in-crisis-but-not-for-the-reason-you-may-think-52349">in a bit of a pickle</a>. We have a great model that can explain the evolution of the universe from a fraction of a second after the big bang, until now approximately 14 billion years later. The problem is that in order to explain all the observations, a mysterious energy called “dark energy” must be added to the models. Dark energy is a huge problem, it accounts for about 70% of all the energy the universe, and we have absolutely no idea what it is.</p>
<p>Dark energy is <em>like</em> an anti-gravitational effect that is pushing the universe apart and causing its expansion to accelerate. So to explain dark energy, cosmologists have attempted to change or replace Einstein’s theory to see if a new theory of spacetime could finally explain the effects of dark energy. </p>
<p>One way that cosmologists tried to do this was by changing the speed in which gravitational waves and light travelled. There were many different theories that had this component – each with a peculiar name like quartic and quintic galileons, vector-tensor theories, generalised proca theories, bigravity theories and so forth. Without data any of the theories could have been correct, and there were many people hopeful that they could be the next Einstein or Newton. </p>
<h2>Where are we now?</h2>
<p>But now in a single observation from a single neutron star merger a wide variety of these have now been consigned to cosmological dustbin in a flurry of papers (<a href="https://arxiv.org/abs/1711.09430">here</a>, <a href="https://arxiv.org/abs/1710.05901">here</a>, <a href="https://arxiv.org/abs/1712.02710">here</a>, <a href="https://arxiv.org/abs/1711.00492">here</a>, <a href="https://arxiv.org/abs/1710.06394">here</a> and <a href="https://arxiv.org/abs/1710.05893">here</a>). So no new Einstein yet.</p>
<p>In the absence of compelling data, it is still possible that we can update Einstein so we can account for dark energy. But the wiggles from the gravitational wave data has left very little wriggle room. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/198775/original/file-20171212-9386-1e2mt25.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of the finished square kilometre array.</span>
<span class="attribution"><span class="source">Swinburne Astronomy Productions for SKA Project Development Office</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>All the theories that have survived the pruning are much simpler than those that were allowed before; and the simplest theory, and the frontrunner, is that dark energy is the energy of empty space, and just happens to have the value we observe.</p>
<p>Another explanation that has survived is that it’s a Higgs-like field. The <a href="https://theconversation.com/nobel-prize-in-physics-goes-to-discovery-of-the-higgs-boson-19014">now famous Higgs boson</a> is a manifestation of a “Higgs field” – the first “scalar field” observed in nature. This is a field that has a value at every point in spacetime, but no direction. An analogy would be a pressure map on a weather forecast (values everywhere but no direction). A wind map, on the other hand, isn’t a scalar field as it has speed and overall direction. Apart from Higgs, all particles in nature are associated with “quantum fields” that aren’t scalar. But like the Higgs, dark energy could be an exception: a ubiquitous scalar field pushing the universe apart in every direction. </p>
<p>Thankfully we won’t have to wait long before <a href="https://theconversation.com/the-experiments-trying-to-crack-physics-biggest-question-what-is-dark-energy-52917">new telescopes</a> will test the remaining theories and a big piece of the cosmological puzzle will be completed.</p><img src="https://counter.theconversation.com/content/88998/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Kitching receives funding from the Royal Society and the Science & Technology Facilities Council.</span></em></p>Cosmologists who were hoping to be the next Einstein have had to bin their theories.Thomas Kitching, Reader in Astrophysics, UCLLicensed as Creative Commons – attribution, no derivatives.