tag:theconversation.com,2011:/au/topics/ligo-24713/articles
LIGO – The Conversation
2023-06-30T20:57:15Z
tag:theconversation.com,2011:article/208815
2023-06-30T20:57:15Z
2023-06-30T20:57:15Z
A subtle symphony of ripples in spacetime – astronomers use dead stars to measure gravitational waves produced by ancient black holes
<figure><img src="https://images.theconversation.com/files/535073/original/file-20230630-14361-kaueuz.jpg?ixlib=rb-1.1.0&rect=38%2C76%2C4547%2C2919&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Black holes and other massive objects create ripples in spacetime when they merge.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/black-holes-illustration-royalty-free-illustration/1088377636?phrase=gravitational+waves&adppopup=true">Victor de Schwanburg/Science Photo Library via Getty Images</a></span></figcaption></figure><p>An international team of astronomers has detected a <a href="https://doi.org/10.3847/2041-8213/acdac6">faint signal</a> of gravitational waves reverberating through the universe. By using dead stars as a giant network of <a href="https://iopscience.iop.org/collections/apjl-230623-245-Focus-on-NANOGrav-15-year">gravitational wave detectors</a>, the collaboration – called <a href="https://nanograv.org/">NANOGrav</a> – was able to measure a low-frequency hum from a chorus of <a href="https://theconversation.com/why-astrophysicists-are-over-the-moon-about-observing-merging-neutron-stars-84957">ripples of spacetime</a>.</p>
<p>I’m an <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en">astronomer</a> who studies and has written about <a href="https://wwnorton.com/books/9780393343861">cosmology</a>, <a href="https://wwnorton.com/books/9780393357509">black holes</a> and <a href="https://www.penguinrandomhouse.com/books/718149/worlds-without-end-by-chris-impey/">exoplanets</a>. I’ve researched the <a href="https://www.cambridge.org/core/journals/proceedings-of-the-international-astronomical-union/article/survey-of-agn-and-supermassive-black-holes-in-the-cosmos-survey/B1ADC49E96B9D865D55188EC839ED033">evolution of supermassive black holes</a> using the Hubble Space telescope.</p>
<p>Though members of the team behind this new discovery aren’t yet certain, they strongly suspect that the background hum of gravitational waves they measured was caused by countless ancient merging events of supermassive black holes.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/zsDOqLWuWQ4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Pulsars are spinning dead stars that emit strong beams of radiation and can be used as accurate cosmic clocks.</span></figcaption>
</figure>
<h2>Using dead stars for cosmology</h2>
<p><a href="https://www.ligo.caltech.edu/page/what-are-gw">Gravitational waves</a> are ripples in spacetime caused by massive accelerating objects. Albert Einstein predicted their existence in his <a href="https://theconversation.com/why-does-gravity-pull-us-down-and-not-up-162141">general theory of relativity</a>, in which he hypothesized that when a gravitational wave passes through space, it makes the space shrink then expand periodically.</p>
<p>Researchers first detected direct evidence of gravitational waves in 2015, when the <a href="https://theconversation.com/gravitational-wave-detector-ligo-is-back-online-after-3-years-of-upgrades-how-the-worlds-most-sensitive-yardstick-reveals-secrets-of-the-universe-204339">Laser Interferometer Gravitational-Wave Observatory, known as LIGO</a>, <a href="https://theconversation.com/what-happens-when-ligo-texts-you-to-say-its-detected-one-of-einsteins-predicted-gravitational-waves-53259">picked up a signal</a> from a <a href="https://www.ligo.caltech.edu/detection">pair of merging black holes</a> that had traveled 1.3 billion light-years to reach Earth.</p>
<p>The NANOGrav collaboration is also trying to detect spacetime ripples, but on an interstellar scale. The team <a href="https://theconversation.com/fifty-years-ago-jocelyn-bell-discovered-pulsars-and-changed-our-view-of-the-universe-88083">used pulsars</a>, rapidly spinning dead stars that emit a beam of radio emissions. Pulsars are functionally similar to a lighthouse – as they spin, their beams can sweep across the Earth at <a href="https://nanograv.org/science/topics/pulsars-cosmic-clocks">regular intervals</a>.</p>
<p>The NANOGrav team used pulsars that <a href="https://doi.org/10.3847/2041-8213/acda9a">rotate incredibly fast</a> – up to 1,000 times per second – and these pulses can be timed like the ticking of an <a href="https://nanograv.org/science/topics/pulsars-cosmic-clocks">extremely accurate cosmic clock</a>. As gravitational waves sweep past a pulsar at the speed of light, the waves will very slightly expand and contract the distance between the pulsar and the Earth, ever so slightly changing the time between the ticks. </p>
<p>Pulsars are such accurate clocks that it is possible to measure their ticking with an accuracy to within 100 nanoseconds. That lets astronomers calculate the distance between a pulsar and Earth to within <a href="https://astronomy.swin.edu.au/cosmos/p/Pulsar+Timing">100 feet</a> (30 meters). Gravitational waves change the distance between these pulsars and Earth by tens of miles, making pulsars easily sensitive enough to detect this effect.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A giant, white reflecting dish with a receiver." src="https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/535071/original/file-20230630-17-5kb781.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The NANOGrav team used a number of radio telescopes, including the Green Bank Telescope in West Virginia, to listen to pulsars for 15 years.</span>
<span class="attribution"><a class="source" href="https://public.nrao.edu/gallery/green-bank-telescope/">NRAO/AUI/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Finding a hum within cacophony</h2>
<p>The first thing the NANOGrav team had to do was control for the <a href="https://doi.org/10.3847/2041-8213/acda88">noise in its cosmic gravitational wave detector</a>. This included <a href="https://theconversation.com/radio-interference-from-satellites-is-threatening-astronomy-a-proposed-zone-for-testing-new-technologies-could-head-off-the-problem-199353">noise in the radio receivers</a> it used and subtle astrophysics that affect the behavior of pulsars. Even accounting for these effects, the team’s approach was not sensitive enough to detect gravitational waves from <a href="https://doi.org/10.48550/arXiv.2306.16222">individual supermassive black hole binaries</a>. However, it had enough sensitivity to detect the sum of all the massive black hole mergers that have occurred anywhere in the universe since the Big Bang – as many as a million overlapping signals.</p>
<p>In a musical analogy, it is like standing in a busy downtown and hearing the faint sound of a symphony somewhere in the distance. You can’t pick out a single instrument because of the noise of the cars and the people around you, but you can hear the hum of a hundred instruments. The team had to tease out the signature of this <a href="https://www.space.com/gravitational-wave-background-universe-1st-detection">gravitational wave “background”</a> from other competing signals.</p>
<p>The team was able to detect this symphony by measuring a network of 67 different pulsars for 15 years. If some disruption in the ticking of one pulsar was due to gravitational waves from the distant universe, all the pulsars the team was watching would be affected in a similar way. On June 28, 2023, the team published <a href="https://www.nytimes.com/2023/06/28/science/astronomy-gravitational-waves-nanograv.html">four papers</a> describing its project and the evidence it found of the gravitational wave background.</p>
<p>The hum the NANOGrav collaboration found is produced from the merging of black holes that are billions of times more massive than the Sun. These black holes spin around one another very slowly and produce gravitational waves with <a href="https://www.scienceinschool.org/article/2017/gravitational-waves-taxonomy/">frequencies of one-billionth of a hertz</a>. That means the spacetime ripples have an oscillation every few decades. This slow oscillation of the wave is the reason the team needed to rely on the incredibly accurate timekeeping of pulsars.</p>
<p>These gravitational waves are different from <a href="https://theconversation.com/ligo-announcement-vaults-astronomy-out-of-its-silent-movie-era-into-the-talkies-85727">the waves LIGO can detect</a>. LIGO’s signals are produced when two black holes <a href="https://media.ligo.northwestern.edu/gallery/mass-plot">10 to 100 times the mass of the Sun</a> merge into one rapidly spinning object, creating gravitational waves that oscillate hundreds of times per second.</p>
<p>If you think of black holes as a tuning fork, the smaller the event, the faster the tuning fork vibrates and the higher the pitch. LIGO detects gravitational waves that “ring” in the audible range. The black hole mergers the NANOGrav team has found “ring” with a frequency billions of times too low to hear. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A star-filled sky with many spiral galaxies." src="https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=610&fit=crop&dpr=1 600w, https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=610&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=610&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=767&fit=crop&dpr=1 754w, https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=767&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/535068/original/file-20230630-15-bjzonq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=767&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 James Webb Space Telescope has allowed astronomers to peer back in time and study the first galaxies to form after the Big Bang.</span>
<span class="attribution"><a class="source" href="https://webbtelescope.org/contents/media/images/2022/038/01G7JGTH21B5GN9VCYAHBXKSD1">NASA, ESA, CSA, STScI</a></span>
</figcaption>
</figure>
<h2>Giant black holes in the early universe</h2>
<p>Astronomers have long been interested in <a href="https://theconversation.com/james-webb-space-telescope-an-astronomer-explains-the-stunning-newly-released-first-images-186800">studying how stars and galaxies first emerged</a> in the aftermath of the Big Bang. This new finding from the NANOGrav team is like adding another color – gravitational waves – to the picture of the early universe that is just starting to emerge, in large part thanks to <a href="https://theconversation.com/the-james-webb-space-telescope-is-finally-ready-to-do-science-and-its-seeing-the-universe-more-clearly-than-even-its-own-engineers-hoped-for-184989">the James Webb Space Telescope</a>.</p>
<p>A major scientific goal of the <a href="https://webbtelescope.org/home">James Webb Space Telescope</a> is to help researchers study how the first stars and galaxies formed after the Big Bang. To do this, James Webb was designed to detect the faint light from incredibly distant stars and galaxies. The farther away an object is, the longer it takes the light to get to Earth, so James Webb is effectively a time machine that can peer back over 13.5 billion years to see light from the <a href="https://webb.nasa.gov/content/science/firstLight.html">first stars and galaxies</a> in the universe. </p>
<p>It has been very successful in the quest, having found <a href="https://www.space.com/james-webb-space-telescope-galaxies-early-universe-first-light">hundreds of galaxies</a> that flooded the universe with light in the first 700 million years after the big bang. The telescope has also detected the <a href="https://www.livescience.com/james-webb-space-telescope-discovers-oldest-black-hole-in-the-universe-a-cosmic-monster-ten-million-times-heavier-than-the-sun">oldest black hole</a> in the universe, located at the center of a galaxy that formed just 500 million years after the Big Bang.</p>
<p>These findings are challenging existing theories of the evolution of the universe. </p>
<p>It takes a long time to <a href="https://www.smithsonianmag.com/smart-news/webb-telescope-finds-evidence-of-massive-galaxies-that-defy-theories-of-the-early-universe-180981689/">grow a massive galaxy</a>. Astronomers know that supermassive black holes <a href="https://theconversation.com/say-hello-to-sagittarius-a-the-black-hole-at-the-center-of-the-milky-way-galaxy-183008">lie at the center of every galaxy</a> and have mass proportional to their host galaxies. So these ancient galaxies almost certainly have <a href="https://ec.europa.eu/research-and-innovation/en/horizon-magazine/how-did-supermassive-black-holes-grow-so-fast">the correspondingly massive black hole</a> in their centers.</p>
<p>The problem is that the objects James Webb has been finding are far bigger than current theory says they should be. </p>
<p>These new results from the NANOGrav team emerged from astronomers’ first opportunity to listen to the gravitational waves of the ancient universe. The findings, while tantalizing, <a href="https://doi.org/10.1038/d41586-023-02167-7">aren’t quite strong enough to claim a definitive discovery</a>. That will likely change, as the team has expanded its pulsar network <a href="https://nanograv.org/news/15yrRelease">to include 115 pulsars</a> and should get results from this next survey around 2025. As James Webb and other research challenges existing theories of how galaxies evolved, the ability to study the era after the Big Bang using gravitational waves could be an invaluable tool.</p><img src="https://counter.theconversation.com/content/208815/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation.</span></em></p>
Astronomers have for the first time detected the background hum of gravitational waves likely caused by merging black holes.
Chris Impey, University Distinguished Professor of Astronomy, University of Arizona
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/204339
2023-05-22T12:27:17Z
2023-05-22T12:27:17Z
Gravitational 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 State
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/162785
2021-06-17T20:05:52Z
2021-06-17T20:05:52Z
Approaching zero: super-chilled mirrors edge towards the borders of gravity and quantum physics
<figure><img src="https://images.theconversation.com/files/406468/original/file-20210615-3629-ntfm3c.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2746%2C1835&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Caltech / MIT / LIGO Lab</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The <a href="https://www.ligo.caltech.edu">LIGO gravitational wave observatory</a> in the United States is so sensitive to vibrations it can detect the tiny ripples in space-time called gravitational waves. These waves are caused by colliding black holes and other stellar cataclysms in distant galaxies, and they cause movements in the observatory much smaller than a proton. </p>
<p>Now we have used this sensitivity to effectively chill a 10-kilogram mass down to less than one billionth of a degree above absolute zero.</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>Temperature is a measure of how much, and how fast, the atoms and molecules that surround us (and that we are made of) are moving. When objects cool down, their molecules move less. </p>
<p>“Absolute zero” is the point where atoms and molecules stop moving entirely. However, quantum mechanics says the complete absence of motion is not really possible (due to the <a href="https://theconversation.com/explainer-heisenbergs-uncertainty-principle-7512">uncertainty principle</a>). </p>
<p>Instead, in quantum mechanics the temperature of absolute zero corresponds to a “motional ground state”, which is the theoretical minimum amount of movement an object can have. The 10-kilogram mass in our experiment is about 10 trillion times heavier than the previous heaviest mass cooled to this kind of temperature, and it was cooled to nearly its motional ground state.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/406467/original/file-20210615-22-jxtfky.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">One of the four Advanced LIGO 40-kg mirrors that are cooled near their quantum ground state.</span>
<span class="attribution"><span class="source">Danny Sellers / Caltech / MIT / LIGO Lab</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The work, <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.abh2634">published today in Science</a>, is an important step in the ongoing quest to understand the gap between quantum mechanics — the strange science that rules the universe at very small scales — and the macroscopic world we see around us. </p>
<p>Plans are already under way to improve the experiment in more sensitive gravitational wave observatories of the future. The results may offer insight into the inconsistency between quantum mechanics and the theory of general relativity, which describes gravity and the behaviour of the universe at very large scales.</p>
<h2>How it works</h2>
<p>LIGO detects gravitational waves using lasers fired down long tunnels and bounced between two pairs of 40-kilogram mirrors, then combined to produce an interference pattern. Tiny changes in the distance between the mirrors show up as fluctuations in the laser intensity.</p>
<p>The motion of the four mirrors is controlled very precisely, to isolate them from any surrounding vibrations and even to compensate for the impact of the laser light bouncing off them. </p>
<p>This part may be hard to get your head around, but we can show mathematically that the <em>differences</em> in the motion of the four 40-kilogram mirrors is equivalent to the motion of a single 10-kilogram mirror. What this means is that the pattern of laser intensity changes we observe in this experiment is the same as what we would see from a single 10-kilogram mirror.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/406464/original/file-20210615-22-lyn95.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/406464/original/file-20210615-22-lyn95.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/406464/original/file-20210615-22-lyn95.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/406464/original/file-20210615-22-lyn95.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/406464/original/file-20210615-22-lyn95.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/406464/original/file-20210615-22-lyn95.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/406464/original/file-20210615-22-lyn95.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/406464/original/file-20210615-22-lyn95.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">One of the four Advanced LIGO 40-kg mirrors that are cooled near their quantum ground state.</span>
<span class="attribution"><span class="source">Matt Heintze / Caltech / MIT / LIGO Lab</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Although the temperature of the 10-kilogram mirror is defined by the motion of the atoms and molecules that make it up, we don’t measure the motion of the individual molecules. Instead, and largely because it’s how we measure gravitational waves, we measure the average motion of all the atoms (or the centre-of-mass motion). </p>
<p>There are at least as many ways the atoms can move as there are atoms, but we only measure one of those ways, and that particular dance move of all the atoms together is the only one we cooled. </p>
<p>The result is that while the four physical mirrors remain at room temperature and would be warm to the touch (if we let anyone touch them), the average motion of the 10-kilogram system is effectively at 0.77 nanokelvin, or less than one billionth of a degree above absolute zero.</p>
<h2>Squeezed light</h2>
<p>Our contribution to Advanced LIGO, as members of Australia’s <a href="https://www.ozgrav.org">OzGrav</a> gravitational wave research centre, was to design, install and test the “quantum squeezed light” system in the detector. This system creates and injects a specially engineered quantum field into the detector, making it more sensitive to the motion of the mirrors, and thus more sensitive to gravitational waves.</p>
<p>The squeezed light system uses a special kind of crystal to produce pairs of highly correlated or “entangled” photons, which reduce the amount of noise in the system. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/406911/original/file-20210617-19-zlv9gg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/406911/original/file-20210617-19-zlv9gg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=257&fit=crop&dpr=1 600w, https://images.theconversation.com/files/406911/original/file-20210617-19-zlv9gg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=257&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/406911/original/file-20210617-19-zlv9gg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=257&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/406911/original/file-20210617-19-zlv9gg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=323&fit=crop&dpr=1 754w, https://images.theconversation.com/files/406911/original/file-20210617-19-zlv9gg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=323&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/406911/original/file-20210617-19-zlv9gg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=323&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Australian National University scientists Nutsinee Kijbunchoo and Terry McRae 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 class="license">Author provided</span></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/were-going-to-get-a-better-detector-time-for-upgrades-in-the-search-for-gravitational-waves-100382">We're going to get a better detector: time for upgrades in the search for gravitational waves</a>
</strong>
</em>
</p>
<hr>
<h2>What does it all mean?</h2>
<p>Being able to observe one particular property of these mirrors approach a quantum ground state is a by-product of improving LIGO in the quest to do more and better gravitational wave astronomy, but it might also offer insights into the vexed question of quantum mechanics and gravity. </p>
<p>At very small scales, quantum mechanics allows many strange phenomena, such as objects being both waves and particles, or seemingly existing in two places at the same time. However, even though the macroscopic world we see is built from tiny objects that must obey quantum phenomena, we don’t see these quantum effects at larger scales. </p>
<p>One theory about why this happens is the idea of <em>decoherence</em>. This suggests that heat and vibrations from a quantum system’s surroundings disrupt its quantum state and make it behave like a familiar solid object.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/406465/original/file-20210615-15-a86of1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">One of the four Advanced LIGO 40-kg mirrors that are cooled near their quantum ground state.</span>
<span class="attribution"><span class="source">Danny Sellers / Caltech / MIT / LIGO Lab</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>In order to measure gravitational waves, LIGO is designed to not be affected by heat or vibrations from its surroundings, but LIGO test masses are heavy enough for gravity to be a possible cause of decoherence. </p>
<p>Despite a century of searching, we have no way to reconcile gravity and quantum mechanics. Experiments like this, especially if they can get even closer to the ground state, might yield insight into this puzzle. </p>
<p>As we improve LIGO over the next few years, we can re-do this quantum mechanics experiment and maybe see what happens when we cross over from the classical world into the quantum world with human-sized objects.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-gravity-5256">Explainer: gravity</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/162785/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Ernest McClelland receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Robert Ward has received funding from the Australian Research Council</span></em></p><p class="fine-print"><em><span>Terry McRae receives funding from the Australian Research Council. </span></em></p>
The world’s biggest gravitational wave observatory is now probing the limits of quantum mechanics.
David Ernest McClelland, Distinguised Professor and Director Centre for Gravitational Astrophysics, Australian National University
Robert Ward, Associate Investigator, OzGrav (ARC Centre of Excellence for Gravitational Wave Discovery), Research Fellow in Physics, Australian National University
Terry McRae, Research fellow, gravitational wave detection, Australian National University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/145474
2020-09-02T14:11:17Z
2020-09-02T14:11:17Z
Gravitational waves: astronomers spot a black hole so massive they weren’t sure it could exist
<figure><img src="https://images.theconversation.com/files/356082/original/file-20200902-24-b5p3wk.jpg?ixlib=rb-1.1.0&rect=112%2C48%2C1805%2C1028&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist impression of merging black holes.</span> <span class="attribution"><span class="source">Mark Myers, ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)</span></span></figcaption></figure><p>One of the greatest things about being an astrophysicist is that you keep discovering things you didn’t think were possible. Now the <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">Laser Interferometer Gravitational-wave Observatory (LIGO)</a> and Virgo Observatory have discovered their largest black hole yet. It’s important because scientists had in fact doubted whether black holes of this mass could even exist.</p>
<p>After months of painstaking analysis, the team has just reported their discovery in papers in the <a href="https://doi.org/10.1103/PhysRevLett.125.101102">Physical Review Letters</a> and the <a href="https://doi.org/10.3847/2041-8213/aba493">Astrophysical Journal Letters</a>.</p>
<p>The black hole was discovered because its merger with a slightly less massive companion emitted gravitational waves. These are <a href="https://theconversation.com/explainer-what-are-gravitational-waves-53239">ripples in spacetime</a> that can be detected on Earth – the echoes of violent cosmic collisions that, in this case, happened billions of years ago. </p>
<p>The finding is hugely important from a research perspective. It also settles a bet among astrophysicists. In February 2017, a number of us met at the <a href="https://www.aspenphys.org/">Aspen Center for Physics</a> in Colorado, USA. We were excited to be discussing the results <a href="https://theconversation.com/gravitational-waves-found-the-inside-story-54589">that we already had from LIGO</a>. But we were also looking forward to future discoveries and arguing about how pairs of black holes actually merge.</p>
<p>There were multiple ideas under discussion. One was that pairs of massive stars gradually evolve side by side until both collapse into black holes and ultimately merge. Another was that previously unacquainted black holes can be brought together by the jostling of a crowd of other stars in dense stellar regions. But which is the main process? I got several participants together to make a wager, as shown on the photo below. </p>
<figure class="align-center ">
<img alt="Image of the astrophysicists signing the wager." src="https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/356075/original/file-20200902-14-11uxe1b.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">Sourav Chatterjee (now at Tata.
Institute of Fundamental Research, India); Carl Rodriguez (Carnegie
Mellon University, USA); me; Daniel Holz (University of Chicago, USA); Chris Belczynski (Nicolaus Copernicus Astronomical Center, Poland).</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Violent stellar deaths</h2>
<p>At the end of their lives – when stars run out of nuclear fuel and no longer have the support pressure to counter their own gravity – they collapse. Low-mass stars, including our Sun, eventually become faint stellar ghosts <a href="https://imagine.gsfc.nasa.gov/science/objects/dwarfs2.html#:%7E:text=A%20white%20dwarf%20is%20what,core%20of%20the%20star%20remains">known as “white dwarfs”</a>. Stars that started out heavier than about eight times the mass of the Sun become incredibly dense and small objects <a href="https://www.nasa.gov/mission_pages/GLAST/science/neutron_stars.html">called neutron stars</a>. And really massive stars of more than 20 solar masses at birth become black holes, with final masses between a few and around 40 solar masses. </p>
<p>But something weird has long been conjectured to happen to very, very massive stars, perhaps those with initial masses between around 130 and 250 solar masses, whose centres get really hot (around a billion degrees Kelvin) late in their evolution. The light bouncing around inside these stars, and providing much of the pressure support, is so energetic that it can transform into pairs of electrons and positrons (positrons are the antimatter counterparts of electron - they are nearly identical but have opposite charge). </p>
<p>This, in turn, makes the star unstable: the pressure suddenly drops, the centre of the star contracts and heats up, and runaway nuclear fusion causes the entire star to explode in a bright <a href="https://www.quantamagazine.org/long-lived-stellar-blast-kindles-hope-of-a-pair-instability-supernova-20190912/">“pair-instability” supernova</a>, leaving no remnant behind. </p>
<p>This means that, if all black holes in merging pairs were created by collapsing stars, there should be no black holes with masses between around 55 and 130 solar masses – the stars that could have produced such remnants would have ended their lives in explosions that leave nothing behind. More massive black holes, however, can be formed from even heavier stars (of more than 250 solar masses) which do not undergo the same runaway nuclear fusion, and collapse completely into black holes. </p>
<p>But this wouldn’t be the case for black holes merging in a crowd. When two black holes merge, they create another black hole, almost as heavy as the sum of their masses. If this black hole remains in the dense environment it can merge again, giving rise to even more massive black holes of a range of sizes, filling in the mass gap. This is what brought us to signing this bet in Aspen: would we find a merging black hole with mass between around 55 and 130 solar masses or not?</p>
<h2>Filling the (mass) gap</h2>
<p>GW190521 is a merger of two very massive black holes indeed, the heaviest of any observed so far through gravitational waves. The heavier one, measured to be between 71 and 106 solar masses (at 90% confidence), falls squarely into the mass gap. This seems to suggest that black holes do indeed repeatedly merge.</p>
<figure class="align-center ">
<img alt="Artist impression of merging black holes." src="https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/356083/original/file-20200902-20-ujhli0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The merged hole had a final mass of 142 times that of the sun, making it the largest of its kind observed in gravitational waves to date.</span>
<span class="attribution"><span class="source">LIGO/Caltech/MIT/R. Hurt (IPAC).</span></span>
</figcaption>
</figure>
<p>I was not involved in this marvellous measurement. But by a
fortuitous coincidence I had the opportunity to referee one of the discovery papers, meaning that I am now well-prepared to perform my duties as arbiter of the bet. My first order of business is to adjudicate the wager in favour of Chatterjee and Rodriguez as well as Fred Rasio of Northwestern University, US, who joined the ultimate winners in an addendum after the original bet was signed.</p>
<figure class="align-right ">
<img alt="Picture of the wager text." src="https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=731&fit=crop&dpr=1 600w, https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=731&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=731&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=919&fit=crop&dpr=1 754w, https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=919&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/356073/original/file-20200902-24-172yc7r.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=919&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The bet.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Congratulations to the deserved winners – and may they enjoy the wine
owed to them, and the pleasure of being proved right. The bet being resolved, my next to-do item, along with many other astrophysicists around the world, is to start thinking about the implications of this revolutionary observation. </p>
<p>Is this the definitive demonstration of black holes merging repeatedly in a dense cluster of stars? Could we have incorrectly estimated the boundaries of the mass gap because of uncertainty in key nuclear reactions? Could the merger have happened in completely different ways we haven’t even thought of?</p>
<p>The LIGO-Virgo teams have yet again done an amazing job with their
instruments and data analysis, obtaining a wonderfully unexpected result.
For the rest of the astrophysics community, the fun of making sense of it is only just beginning. Which is why, in such scientific bets, everybody really is a winner.</p><img src="https://counter.theconversation.com/content/145474/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ilya Mandel receives funding from the Australian Research Council. </span></em></p>
New discovery settles a wager between astrophysicists: black holes can merge repeatedly.
Ilya Mandel, Honorary Professor of Theoretical Astrophysics, University of Birmingham
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/116267
2019-05-03T05:53:05Z
2019-05-03T05:53:05Z
We’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 Sydney
Eric Thrane, Associate professor, Monash University
Qi Chu, Research fellow, The University of Western Australia
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/107962
2018-12-03T13:06:06Z
2018-12-03T13:06:06Z
New 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 Australia
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/86104
2017-10-24T20:18:24Z
2017-10-24T20:18:24Z
Cosmic alchemy: Colliding neutron stars show us how the universe creates gold
<figure><img src="https://images.theconversation.com/files/191637/original/file-20171024-30571-frs0vu.jpg?ixlib=rb-1.1.0&rect=96%2C0%2C803%2C573&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Illustration of hot, dense, expanding cloud of debris stripped from the neutron stars just before they collided.</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/12740">NASA's Goddard Space Flight Center/CI Lab</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>For thousands of years, humans have searched for a way to turn matter into gold. <a href="https://doi.org/10.1086/660139">Ancient alchemists</a> considered this precious metal to be the highest form of matter. As human knowledge advanced, the mystical aspects of alchemy gave way to the sciences we know today. And yet, with all our advances in science and technology, the origin story of gold remained unknown. Until now. </p>
<p>Finally, scientists know how the universe makes gold. Using our <a href="https://doi.org/10.3847/2041-8213/aa91c9">most advanced telescopes and detectors</a>, we’ve seen it created in the cosmic fire of the two colliding stars first detected by LIGO via the gravitational wave they emitted.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/191658/original/file-20171024-30605-ei0pxa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&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 electromagnetic radiation captured from GW170817 now confirms that elements heavier than iron are synthesized in the aftermath of neutron star collisions.</span>
<span class="attribution"><a class="source" href="https://www.caltech.edu/news/caltech-led-teams-strike-cosmic-gold-80074">Jennifer Johnson/SDSS</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Origins of our elements</h2>
<p>Scientists have been able to piece together where many of the elements of the periodic table come from. The Big Bang <a href="https://doi.org/10.1146/annurev.nucl.56.080805.140437">created hydrogen</a>, the lightest and most abundant element. As stars shine, they fuse hydrogen into heavier elements like carbon and oxygen, the elements of life. In their dying years, stars create the common metals – aluminum and iron – and blast them out into space in different types of <a href="https://doi.org/10.1146/annurev.astro.38.1.191">supernova</a> <a href="https://doi.org/10.1146/annurev-astro-082708-101737">explosions</a>.</p>
<p>For decades, scientists have theorized that these stellar explosions also explained the origin of the heaviest and most rare elements, like gold. But they were missing a piece of the story. It hinges on the object left behind by the death of a massive star: a neutron star. Neutron stars pack one-and-a-half times the mass of the sun into a ball only 10 miles across. A teaspoon of material from their surface would weigh 10 million tons.</p>
<p>Many stars in the universe are in binary systems – two stars bound by gravity and orbiting around each other (think Luke’s home planet’s suns in “Star Wars”). A pair of massive stars might eventually end their lives as a pair of neutron stars. The neutron stars orbit each other for hundreds of millions of years. But Einstein says that their dance cannot last forever. Eventually, they must collide.</p>
<h2>Massive collision, detected multiple ways</h2>
<p>On the morning of August 17, 2017, a ripple in space passed through our planet. It was detected by the LIGO and Virgo gravitational wave detectors. This cosmic disturbance came from a pair of city-sized neutron stars colliding at one third the speed of light. The <a href="https://doi.org/10.1103/PhysRevLett.119.161101">energy of this collision</a> surpassed any atom-smashing laboratory on Earth.</p>
<p>Hearing about the collision, astronomers around the world, <a href="http://kilonova.org/about.html">including</a> <a href="https://dabrown.expressions.syr.edu/">us</a>, jumped into action. Telescopes large and small scanned the patch of sky where the gravitational waves came from. Twelve hours later, three telescopes caught sight of a brand new star – called a kilonova – in a galaxy called NGC 4993, about 130 million light years from Earth.</p>
<p>Astronomers had captured the light from the cosmic fire of the colliding neutron stars. It was time to point the world’s biggest and best telescopes toward the new star to see the visible and infrared light from the collision’s aftermath. In Chile, the Gemini telescope swerved its large 26-foot mirror to the kilonova. NASA steered the Hubble to the same location.</p>
<figure>
<img src="http://kilonova.org/img/DECam_fading_kn_final.gif">
<figcaption><span class="caption">Movie of the visible light from the kilonova fading away in the galaxy NGC 4993, 130 million light years away from Earth.</span></figcaption>
</figure>
<p>Just like the embers of an intense campfire grow cold and dim, the afterglow of this cosmic fire quickly faded away. Within days the visible light faded away, leaving behind a warm infrared glow, which eventually disappeared as well. </p>
<h2>Observing the universe forging gold</h2>
<p>But in this fading light was encoded the answer to the age-old question of how gold is made.</p>
<p>Shine sunlight through a prism and you will see our sun’s spectrum – the colors of the rainbow spread from short wavelength blue light to long wavelength red light. This spectrum contains the fingerprints of the elements bound up and forged in the sun. Each element is marked by a unique fingerprint of lines in the spectrum, reflecting the different atomic structure.</p>
<p>The spectrum of the kilonova contained the fingerprints of the heaviest elements in the universe. Its light carried the telltale signature of the neutron-star material decaying into platinum, gold and other so-called <a href="https://en.wikipedia.org/wiki/R-process">“r-process” elements</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/191689/original/file-20171024-30613-1iljobe.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">Visible and infrared spectrum of the kilonova. The broad peaks and valleys in the spectrum are the fingerprints of heavy element creation.</span>
<span class="attribution"><span class="source">Matt Nicholl</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>For the first time, humans had seen alchemy in action, the universe turning matter into gold. And not just a small amount: This one collision created at least 10 Earths’ worth of gold. You might be wearing some gold or platinum jewelry right now. Take a look at it. That metal was created in the atomic fire of a neutron star collision in our own galaxy billions of years ago – a collision just like the one seen on August 17.</p>
<p>And what of the gold produced in this collision? It will be blown out into the cosmos and mixed with dust and gas from its host galaxy. Perhaps one day it will form part of a new planet whose inhabitants will embark on a millennia-long quest to understand its origin.</p><img src="https://counter.theconversation.com/content/86104/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Duncan Brown receives funding from the National Science Foundation and the Research Corporation for Science Advancement.</span></em></p><p class="fine-print"><em><span>Edo Berger receives funding from the National Science Foundation and NASA. </span></em></p>
Until the recent observation of merging neutron stars, how the heaviest elements come to be was a mystery. But their fingerprints are all over this cosmic collision.
Duncan Brown, Professor of Physics, Syracuse University
Edo Berger, Professor of Astronomy, Harvard University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/85727
2017-10-16T14:12:17Z
2017-10-16T14:12:17Z
LIGO announcement vaults astronomy out of its silent movie era into the talkies
<figure><img src="https://images.theconversation.com/files/190302/original/file-20171016-27747-10xe6lo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Supercomputer simulation of a pair of neutron stars colliding.</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/11530">NASA/AEI/ZIB/M. Koppitz and L. Rezzolla</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>When <a href="https://theconversation.com/what-happens-when-ligo-texts-you-to-say-its-detected-one-of-einsteins-predicted-gravitational-waves-53259">LIGO detected its first gravitational wave</a> back in September 2015, I was pretty excited to say the least. As part of a decades-long endeavor, our whole team was ecstatic to observe gravitational waves – <a href="https://www.ligo.caltech.edu/page/what-are-gw">which are literally ripples in space</a> – caused by two black holes smashing together. It was the first time that Einstein’s predictions about these tiny ripples were directly confirmed. Just this month, the <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/2017/">Nobel Prize in physics was awarded to three of the founders</a> of our international collaborative effort – Rainer Weiss, Kip Thorne and Barry Barish – in recognition of this first observation.</p>
<p>It may be hard to believe, but today I am even more excited than I was in 2015. For the first time ever, astrophysicists have discovered <a href="https://doi.org/10.1103/PhysRevLett.119.161101">gravitational waves originating from an entirely new source</a>: merging neutron stars.</p>
<p>That’s not all. This new event, GW170817, was accompanied by a host of other observations across the electromagnetic spectrum <a href="https://doi.org/10.3847/2041-8213/aa920c">including gamma-rays</a>, X-rays, visible light and <a href="https://doi.org/10.1126/science.aap9855">radio waves</a>. Before, we had detected only gravitational waves on their own, without any other corroborating observations of the source event. This groundbreaking announcement from the <a href="http://www.ligo.org/">LIGO Scientific Collaboration</a> and the <a href="http://www.virgo-gw.eu/">Virgo collaboration</a> heralds the beginning of <a href="https://doi.org/10.3847/2041-8213/aa91c9">a new era in “multi-messenger” astronomy</a>.</p>
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<span class="caption">Various telescopes are focused on different energy wavelengths along the electromagnetic spectrum.</span>
<span class="attribution"><a class="source" href="http://chandra.harvard.edu/resources/illustrations/elec_mag_spec.html">NASA/CXC</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>Until gravitational waves were discovered, astronomy was essentially in its silent film era. Gravitational waves provide something like a long-awaited soundtrack for our universe. The 2015 breakthrough and subsequent gravitational wave observations never managed to synchronize the sights and sounds of the cosmos, though. That changed with the detection of GW170817. Today we celebrate astronomy’s version of “the talkie” with the simultaneous observation of gravitational waves and electromagnetic radiation from the same source.</p>
<h2>A text alert with big implications</h2>
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<a href="https://images.theconversation.com/files/190284/original/file-20171015-3532-1r6xfxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/190284/original/file-20171015-3532-1r6xfxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/190284/original/file-20171015-3532-1r6xfxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=303&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190284/original/file-20171015-3532-1r6xfxl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=303&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190284/original/file-20171015-3532-1r6xfxl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=303&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190284/original/file-20171015-3532-1r6xfxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=380&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190284/original/file-20171015-3532-1r6xfxl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=380&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190284/original/file-20171015-3532-1r6xfxl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=380&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Original text indicated a potential compact binary coalescence (CBC) – what we know know as the first binary neutron star merger, named GW170817.</span>
<span class="attribution"><span class="source">Chad Hanna</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>On August 17, 2017 at 8:47 a.m. EDT, I received a text message from the LIGO real-time analysis system that indicated a significant gravitational wave candidate had been identified. My text message notification is a simple “Hey!” I’m not a huge texter, so a large fraction of the messages I receive tend to be about gravitational waves. As you might imagine, I have a somewhat Pavlovian response to that “Hey!” </p>
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<a href="https://images.theconversation.com/files/190285/original/file-20171015-3511-1e3ik35.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/190285/original/file-20171015-3511-1e3ik35.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/190285/original/file-20171015-3511-1e3ik35.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=431&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190285/original/file-20171015-3511-1e3ik35.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=431&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190285/original/file-20171015-3511-1e3ik35.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=431&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190285/original/file-20171015-3511-1e3ik35.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=542&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190285/original/file-20171015-3511-1e3ik35.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=542&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190285/original/file-20171015-3511-1e3ik35.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=542&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Institute for Gravitation and the Cosmos, where Penn State researchers keep an eye on real-time updates to the gravitational wave candidate event database (GraCEDb).</span>
<span class="attribution"><span class="source">Chad Hanna</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>At Penn State, we have a small conference room devoted to LIGO real-time analysis where we monitor gravitational wave searches. When I turned to look at our display of the candidate event database, I was shocked. Not only was this new gravitational wave extremely significant, but there was also a coincident gamma-ray burst (GRB).</p>
<p>Given that the LIGO and Virgo collaborations had already detected four gravitational waves known as <a href="https://doi.org/10.1103/PhysRevLett.116.061102">GW150914</a>, <a href="https://doi.org//10.1103/PhysRevLett.116.241103">GW151226</a>, <a href="https://doi.org//10.1103/PhysRevLett.118.221101">GW170104</a> and <a href="https://doi.org//10.1103/PhysRevLett.119.141101">GW170814</a>, it wasn’t that surprising to see another significant gravitational wave candidate that August morning – but one that coincided with a gamma-ray burst was simply surreal.</p>
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<a href="https://images.theconversation.com/files/190250/original/file-20171015-3511-thqs2y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/190250/original/file-20171015-3511-thqs2y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/190250/original/file-20171015-3511-thqs2y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190250/original/file-20171015-3511-thqs2y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190250/original/file-20171015-3511-thqs2y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190250/original/file-20171015-3511-thqs2y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190250/original/file-20171015-3511-thqs2y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190250/original/file-20171015-3511-thqs2y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">LIGO’s previous detections of gravitational waves came from colliding black holes. The latest detection is not pictured and lasted much longer than the scale of this graphic, more than 100 seconds.</span>
<span class="attribution"><a class="source" href="https://www.ligo.caltech.edu/image/ligo20170927d">LIGO/Caltech/MIT/LSC</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>Until that day, LIGO and Virgo had detected gravitational waves only from binary black holes – astronomical phenomena that are unlikely to be associated with an electromagnetic counterpart such as a gamma-ray burst. Despite tremendous effort, researchers hadn’t ever been able to confidently correlate a gravitational wave event with other astronomical observations. </p>
<p>I immediately dialed into the LIGO rapid response teleconference channel and opened my laptop. There I saw the missing link, which was not immediately clear from the text message: The estimated masses of each object that had merged were just 1.2 and 1.5 times the mass of our sun. That’s firmly within the expectations of a new gravitational wave source type: neutron stars.</p>
<p>We had always hoped that one day LIGO would detect a gravitational wave signal simultaneously with other telescopes. In fact, we even thought that two colliding neutron stars would be the most promising source. To increase our chances, LIGO and Virgo have developed a program over the last decade to rapidly analyze gravitational wave data and alert a <a href="http://ligo.org/scientists/GWEMalerts.php">worldwide team of astronomers</a> to our findings so that they can observe the area of interest. LIGO and Virgo also receive alerts of transient astronomical phenomena so researchers can undertake a deeper search of gravitational wave data. It looked like this was finally it.</p>
<h2>Chasing down the confirming data</h2>
<p>For all that had gone right that morning, a few things were bound to go wrong.</p>
<p>We recovered the gravitational wave signal in the LIGO Washington detector data only in real time. Unfortunately, the LIGO Louisiana detector had suffered from a burst of instrumental noise right around the time that the neutron star merger signal had arrived. The Virgo detector data from Italy was clean, but the transatlantic data transfer had stopped due to a network connection outage.</p>
<p>Our group proceeded anyway, and the LIGO rapid response team quickly assembled a notice to be sent to our <a href="https://gcn.gsfc.nasa.gov/gcn3/21505.gcn3">over 70 observing partners</a> – astronomers from all over the world. This was the first notice of around 200 and counting that helped to firmly establish gravitational wave multi-messenger astronomy as a brand new field.</p>
<p>The binary neutron star signal lasted over 100 seconds in LIGO’s data. That’s long enough to recover almost all of the signal in spite of the instrumental noise in the LIGO Louisiana data, which affected only the very end of the detected signal.</p>
<p>Eventually, we were able to analyze all three gravitational wave detector data streams to figure out when the signal arrived at each one. Then we triangulated the gravitational wave source on the sky to a sufficiently small area that astronomers could survey the entire region. </p>
<p>We were fortunate that the <a href="https://www.nasa.gov/content/fermi-gamma-ray-space-telescope">Fermi Gamma-ray Space Telescope</a> was already pointing in the direction of this new gravitational wave when it arrived at Earth. However, astronomers using ground-based telescopes had to wait for nighttime.</p>
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<a href="https://images.theconversation.com/files/190419/original/file-20171016-30971-sdpddh.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/190419/original/file-20171016-30971-sdpddh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/190419/original/file-20171016-30971-sdpddh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=297&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190419/original/file-20171016-30971-sdpddh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=297&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190419/original/file-20171016-30971-sdpddh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=297&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190419/original/file-20171016-30971-sdpddh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=373&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190419/original/file-20171016-30971-sdpddh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=373&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190419/original/file-20171016-30971-sdpddh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=373&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Composite images of the optical counterpart to GW170817. Each image is 1.5 arcseconds on a side. Images are taken two weeks apart.</span>
<span class="attribution"><a class="source" href="http://ligo.org/detections/GW170817.php">Soares-Santos et al. and DES Collaboration</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>About 10 hours after the initial alert, the first news of a visible light counterpart emerged and was independently confirmed by many facilities: A new bright spot that hadn’t been there previously was found in a galaxy in the direction of the gravitational wave. Over the coming hours, days and weeks, we also learned that there were ultraviolet counterparts, X-ray counterparts and even radio waves all associated with the binary neutron star merger. Each complementary observation revealed a new part of the story of how the immensely energetic neutron star matter was flying off into space after the collision.</p>
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<a href="https://images.theconversation.com/files/190427/original/file-20171016-30966-1qjsqhu.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/190427/original/file-20171016-30966-1qjsqhu.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/190427/original/file-20171016-30966-1qjsqhu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190427/original/file-20171016-30966-1qjsqhu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190427/original/file-20171016-30966-1qjsqhu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190427/original/file-20171016-30966-1qjsqhu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190427/original/file-20171016-30966-1qjsqhu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190427/original/file-20171016-30966-1qjsqhu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">We can pinpoint sources like GW170817 by triangulating the three signals. The rapid Hanford-Livingston localization is shown in blue, and the final Hanford-Livingston-Virgo localization is in green. The gray rings are one-sigma triangulation constraints from the three detector pairs.</span>
<span class="attribution"><a class="source" href="http://ligo.org/detections/GW170817.php">LIGO/Virgo/NASA/Leo Singer (Milky Way image: Axel Mellinger)</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>We were lucky to pin down the location of the gravitational wave quickly enough to identify the observational counterparts so early. Nevertheless, next time around, we hope that gravitational wave identification can happen even sooner and at a more favorable time of day so we don’t miss out on the earliest optical emission. Perhaps one day we’ll even be able to use the early gravitational wave emission leading up to a neutron star collision to predict where on the sky they’ll merge and have telescopes already pointed in that direction, ready for the show.</p>
<h2>Future of multi-messenger astronomy with LIGO</h2>
<p>GW170817 confirmed the hypothesis that at least some gamma-ray bursts are in fact <a href="http://theconversation.com/why-astrophysicists-are-over-the-moon-about-observing-merging-neutron-stars-84957">caused by merging neutron stars</a>. It shattered our expectations for how frequently we would be able to associate gamma-ray bursts with gravitational waves and how prevalent other electromagnetic counterparts would be. After all, we’ve been <a href="https://www.ligo.caltech.edu/page/timeline">operating advanced LIGO for only two years</a>!</p>
<p>Our most optimistic hopes have come true with this new gravitational wave, and the team hopes to have many more opportunities like this in the next few years. The future of <a href="https://www.nsf.gov/about/congress/reports/nsf_big_ideas.pdf#page=7">multi-messenger astronomy</a> is very, very bright.</p><img src="https://counter.theconversation.com/content/85727/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 the Charles E. Kaufman Foundation of The Pittsburgh Foundation.</span></em></p>
A LIGO team member describes how the detection of a gravitational wave from a new source – merging neutron stars – vaults astronomy into a new era of ‘multi-messenger’ observations.
Chad Hanna, Assistant Professor of Physics, Penn State
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/84957
2017-10-16T14:03:49Z
2017-10-16T14:03:49Z
Why astrophysicists are over the moon about observing merging neutron stars
<figure><img src="https://images.theconversation.com/files/190212/original/file-20171013-3555-ldwh37.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Simulation of two neutron stars merging.</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/10740">NASA/AEI/ZIB/M. Koppitz and L. Rezzolla</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>When <a href="https://www.ligo.caltech.edu/">LIGO</a>, the Laser Interferometer Gravitational-Wave Observatory, first detected <a href="https://www.ligo.caltech.edu/page/what-are-gw">gravitational waves</a> from merging black holes, it opened up a new window in astrophysics and provided the most powerful confirmation yet of Einstein’s theory of general relativity. Now LIGO has done it again, together with the <a href="https://www.ego-gw.it/public/about/whatIs.aspx">Virgo interferometer</a>, this time by <a href="https://doi.org/10.1103/PhysRevLett.119.161101">observing merging neutron stars</a> – something astrophysicists had known must happen but had never been able to detect definitively until now.</p>
<p>Observing two neutron stars smash together is important for much more than just the thrill of discovery. This news may confirm a longstanding theory: that some gamma-ray bursts (GRBs for short), which are among the most energetic, luminous events in the universe, are the result of merging neutron stars. And it is in the crucible of these mergers that most heavy elements may be forged. Researchers can’t produce anything like the temperatures or pressures of neutron stars in a laboratory, so observation of these exotic objects provides a way to test what happens to matter at such extremes.</p>
<p>Astronomers are excited because for the first time they have gravitational waves and light signals stemming from the same event. These truly independent measurements are separate avenues that together add to the physical understanding of the neutron star merger.</p>
<h2>Gravitational waves just one part of this news</h2>
<p>The LIGO project has thus far announced the detection of four mergers of binary black holes – observed via the gravitational waves they emitted. These are ripples in the fabric of spacetime propagating in all directions, like waves emanating out from a pebble dropped in a pond. Encoded in the gravitational wave signal is information about the pre- and post-merger masses of the objects. Black holes are much more massive than neutron stars, so the energy they release as gravitational waves is much higher. Because light cannot escape from a black hole, you expect (and see) no light from these mergers.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/190240/original/file-20171014-3537-84dvk7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/190240/original/file-20171014-3537-84dvk7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/190240/original/file-20171014-3537-84dvk7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190240/original/file-20171014-3537-84dvk7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190240/original/file-20171014-3537-84dvk7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190240/original/file-20171014-3537-84dvk7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190240/original/file-20171014-3537-84dvk7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190240/original/file-20171014-3537-84dvk7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s rendering of a gamma-ray burst, the most energetic form of light.</span>
<span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/12055">NASA/Swift/Cruz deWilde</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The merger of neutron stars should produce both a gravitational wave and a short gamma-ray burst signal. These brief, incredibly intense flashes of gamma-ray light are seen from galaxies across the universe. They come in two types, classified by their duration. Short GRBs are thought to <a href="https://doi.org/10.1016/j.physrep.2007.02.005">come from the mergers of neutron stars</a>, while long GRBs are known to be coincident with supernovas.</p>
<p>Key to unlocking the mystery of any astronomical object is knowing its distance. In recent years, astronomers have <a href="https://doi.org/10.1086/498107">identified the host galaxies</a> of a <a href="https://doi.org/10.1086/512664">handful of short GRBs</a>. Determining those galaxies’ distances allows astronomers to calculate the power emitted in gamma-rays during the burst, and to determine (or rule out) physical scenarios that could produce that power.</p>
<p>But for LIGO to detect two <a href="https://doi.org/10.1103/PhysRevD.93.112004">neutron stars spiraling in toward each other and merging</a>, it would need to happen relatively nearby – within around 250 million light-years. That such an event was not detected during the first year and a half of LIGO observations already lets astronomers place a constraint on how frequently they happen in the nearby universe.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/190213/original/file-20171013-3537-t0lobc.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/190213/original/file-20171013-3537-t0lobc.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/190213/original/file-20171013-3537-t0lobc.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190213/original/file-20171013-3537-t0lobc.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190213/original/file-20171013-3537-t0lobc.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190213/original/file-20171013-3537-t0lobc.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190213/original/file-20171013-3537-t0lobc.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190213/original/file-20171013-3537-t0lobc.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Galaxy NGC 4993 seemed unassuming enough….</span>
<span class="attribution"><a class="source" href="http://stdatu.stsci.edu/dss/index.html">Palomar Observatory – Space Telescope Science Institute Digital Sky Survey</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>So the rumor of a merging neutron star detection by LIGO with a coincident short gamma-ray burst (<a href="https://gcn.gsfc.nasa.gov/other/170817A.gcn3">GRB170817A</a>) seen by NASA’s <a href="https://fermi.gsfc.nasa.gov/">Fermi Gamma-ray Space Telescope</a> spread through the astronomical community like wildfire this past summer. Astronomers watched from the sidelines as most of the major telescopes in (and above) the world slewed toward an otherwise unremarkable old, nearby (130 million light-years) elliptical galaxy named NGC 4993.</p>
<h2>What we’ve known about neutron stars</h2>
<p>Most stars end their lives relatively calmly; no longer supported by the fusion of hydrogen into helium, their outer layers glide slowly off into space while their cores collapse to the very limits allowed by normal matter – burning embers the size of the Earth called white dwarf stars.</p>
<p>For the rare stars whose masses are a bit higher, 10 to 20 times that of the sun, the picture is a bit different. These stars die the way they lived: quickly and violently, ejecting their outer layers as supernovas and leaving behind something far stranger – a neutron star.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/190251/original/file-20171015-3527-ykrc0b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/190251/original/file-20171015-3527-ykrc0b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/190251/original/file-20171015-3527-ykrc0b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=945&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190251/original/file-20171015-3527-ykrc0b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=945&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190251/original/file-20171015-3527-ykrc0b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=945&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190251/original/file-20171015-3527-ykrc0b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1187&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190251/original/file-20171015-3527-ykrc0b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1187&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190251/original/file-20171015-3527-ykrc0b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1187&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Nobel Prize-winning physicist Subrahmanyan Chandrasekhar.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/AP-A-IL-CX3-OBIT-CHANDRASEKHAR/a3ada89cc6e0da11af9f0014c2589dfb/2/0">AP Photo</a></span>
</figcaption>
</figure>
<p>The details of this story were worked out in 1930 by then 19-year-old Indian astrophysicist <a href="http://chandra.harvard.edu/about/chandra.html">Subrahmanyan Chandrasekhar</a>. He determined precisely how far you can compress normal matter before the relentless pressure of gravity forces electrons into the nuclei of their atoms where they merge with protons to form neutrons. Instead of an Earth-sized remnant, a massive star’s core collapses further to become a highly compressed ball of exotic matter as small as a city but whose mass can be twice that of the sun.</p>
<p>Neutron stars rotate incredibly rapidly. The collapse from millions to tens of kilometers in extent increases their spin due to conservation of angular momentum, like an ice skater pulling in her arms. While the parent star may have rotated once a month, a newly born neutron star can spin hundreds of times per second.</p>
<p>This rapid spinning led to their initial discovery. 50 years ago, Antony Hewish and Jocelyn Bell Burnell <a href="https://www.atnf.csiro.au/outreach/education/everyone/pulsars/index.html">discovered the first radio pulsar</a>: a neutron star emitting radio waves which appear to observers as pulses as the star rotates, like a lighthouse. <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1974/">Hewish would win the 1974 Nobel Prize in physics</a> for this discovery, while Bell Burnell was controversially overlooked.</p>
<p>But what are neutron stars really made of? Are they neutrons all the way through or can they break down further again, into what physicists call “quark soup”? The answer lies in measuring their size. A larger neutron star is mostly neutrons, a smaller star has a more complicated interior made of quarks – the building blocks of protons and neutrons. Untangling how this works is important for our understanding of the fundamental properties of subatomic particles. <a href="https://www.nasa.gov/nicer">A new telescope on the International Space Station</a> aims to address this question by targeting neutron stars and measuring their sizes.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/190239/original/file-20171014-3524-1hqa2i9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/190239/original/file-20171014-3524-1hqa2i9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/190239/original/file-20171014-3524-1hqa2i9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=393&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190239/original/file-20171014-3524-1hqa2i9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=393&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190239/original/file-20171014-3524-1hqa2i9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=393&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190239/original/file-20171014-3524-1hqa2i9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=494&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190239/original/file-20171014-3524-1hqa2i9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=494&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190239/original/file-20171014-3524-1hqa2i9.jpg?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">The orbiting neutron stars rapidly lose energy by emitting gravitational waves and merge after about three orbits, or in less than 8 milliseconds. A black hole forms and the magnetic field becomes more organized, eventually producing structures capable of supporting the jets that power short gamma-ray bursts.</span>
<span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/10740">NASA/AEI/ZIB/M. Koppitz and L. Rezzolla</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>When neutron stars merge</h2>
<p>Over half of all stars are part of binary pairs, and massive stars are more likely to occur in binaries. These pairs of massive stars will co-evolve, and when they die, a pair of neutron stars may remain, orbiting one another.</p>
<p>An orbiting pair of neutron stars loses energy by emitting gravitational waves, and over time this loss of energy will cause them to migrate closer and closer until they eventually collide. While the eventual merger is nearly instantaneous, the gradual inspiral takes tens to hundreds of millions of years, so we expect to see mergers in more evolved galaxies – like NGC 4993, for instance – rather than those that are still rapidly forming new stars.</p>
<p>For decades, it has been <a href="https://doi.org/10.1086/181612">suggested that merging neutron stars</a> may <a href="https://doi.org/10.3847/2041-8205/829/1/L13">provide a mechanism for producing most of the elements</a> on the periodic table heavier than iron. These so-called r-process elements must form in a neutron-rich environment, and have been formed by humans only during the explosion of nuclear bombs.</p>
<p>The signal from such an event is suspected to rapidly cascade through the electromagnetic spectrum, from gamma-rays to X-rays, visible light and infrared. Known as kilonovas, <a href="https://doi.org/10.1038/nature12505">these afterglows have been seen</a> from past short GRBs.</p>
<p>Finally all the pieces fall into place with this gravitational wave detected by the LIGO and Virgo teams, and all the subsequent supporting observations made by astronomers around the world. We know the neutron star masses, the duration of the event, and the distance of the host galaxy. This not only confirms the hypothesis that <a href="https://doi.org/10.3847/2041-8213/aa920c">merging neutron stars produce short GRBs</a>; it lays the foundation for astronomers to produce models of the merger backed both by fundamental physics and real world observations. It’s a rare event to see something new for the first time, and rarer still that it confirms a longstanding theory.</p><img src="https://counter.theconversation.com/content/84957/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Roy Kilgard has received funding from NASA through the Space Telescope Science Institute and from the Smithsonian Astrophysical Observatory.</span></em></p>
The gravitational wave itself is the least exciting part of the announcement from LIGO and Virgo. Observing this new source answers many longstanding questions.
Roy Kilgard, Research Associate Professor of Astronomy, Wesleyan University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/85647
2017-10-16T14:02:45Z
2017-10-16T14:02:45Z
How we discovered gravitational waves from ‘neutron stars’ – and why it’s such a huge deal
<figure><img src="https://images.theconversation.com/files/190387/original/file-20171016-31010-1rr1trx.jpg?ixlib=rb-1.1.0&rect=0%2C243%2C1710%2C1324&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's illustration of two merging neutron stars.</span> <span class="attribution"><span class="source">National Science Foundation/LIGO/Sonoma State University/A. Simonnet.</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Rumours have been <a href="https://www.scientificamerican.com/article/rumors-swell-over-new-kind-of-gravitational-wave-sighting/">swirling for weeks</a> that scientists have detected <a href="https://theconversation.com/explainer-gravitational-waves-and-why-their-discovery-is-such-a-big-deal-53239">gravitational waves</a> – tiny ripples in space and time – from a source other than colliding black holes. Now we can finally confirm that we’ve observed such waves produced by the violent collision of two massive, ultra-dense stars more than 100m light years from the Earth. </p>
<p>The discovery was made on August 17 by the <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">global network of advanced gravitational-wave interferometers</a> – comprising the twin LIGO detectors in the US and their European cousin, Virgo, in Italy. It is hugely important, not least because it helps solve some big mysteries in astrophysics – including the cause of bright flashes of light known as “<a href="https://theconversation.com/flash-aah-aah-could-a-gamma-ray-burst-eradicate-all-life-on-earth-5291">gamma ray bursts</a>” and perhaps even the origins of heavy elements such as gold.</p>
<p>As a member of the LIGO scientific collaboration, I was immediately in raptures as soon as I saw the initial data. And the period that followed was definitely the most intense and sleep deprived, but also incredibly exciting, two months of my career. </p>
<p>The announcement comes just weeks after three scientists <a href="https://theconversation.com/scientists-behind-the-discovery-of-gravitational-waves-win-the-2017-nobel-prize-for-physics-66457">were awarded the Nobel Prize in Physics</a> for their foundational work leading to the discovery of gravitational waves, first announced in February 2016. Since then, detecting gravitational waves from colliding black holes has started to feel like familiar territory – <a href="https://theconversation.com/experiments-simultaneously-detect-gravitational-waves-and-help-open-up-a-new-era-of-astronomy-84818">with four further such events detected</a>. But as far as we know, colliding black holes offer purely a window on the dark side of the universe. We haven’t been able to register light from these events with any other instruments.</p>
<p>But GW170817 – the catchy title for the event of August 17 — changes all that. That’s because the source of the waves this time was two “<a href="https://www.nasa.gov/mission_pages/GLAST/science/neutron_stars.html">neutron stars</a>” – incredibly dense stellar remnants the size of a city, each weighing more than the sun. These stars whizzed around each other at a sizeable fraction of the speed of light before merging in a cataclysmic collision that we’ve now seen shake the very fabric of space and time.</p>
<h2>Mysteries solved</h2>
<p>The cosmic concerto was just beginning, however. Astronomers have long suspected that the merger of two neutron stars could be the overture to a short <a href="https://theconversation.com/flash-aah-aah-could-a-gamma-ray-burst-eradicate-all-life-on-earth-5291">gamma ray burst</a> – an intense flash of gamma-ray light that releases more energy in a fraction of a second than the sun will pump out in ten billion years. For several decades we have observed these gamma ray bursts, but without knowing for sure what causes them.</p>
<p>However, just 1.7 seconds after the gravitational waves from GW170817 arrived at the Earth, <a href="https://www.nasa.gov/content/fermi-gamma-ray-space-telescope/">NASA’s Fermi satellite</a> observed a short burst of gamma rays in the same general region of the sky. LIGO and Virgo had found the smoking gun, and the link between neutron star collisions and short gamma ray bursts was finally and clearly established.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/190392/original/file-20171016-30993-1uxep11.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/190392/original/file-20171016-30993-1uxep11.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190392/original/file-20171016-30993-1uxep11.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190392/original/file-20171016-30993-1uxep11.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190392/original/file-20171016-30993-1uxep11.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190392/original/file-20171016-30993-1uxep11.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190392/original/file-20171016-30993-1uxep11.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Many hands make light (and gravity) work. NASA’s Fermi satellite was instrumental in the discovery.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>The combination of gravitational-wave and gamma-ray observations allowed the position of the cosmic explosion to be pinpointed to less than 30 square degrees on the sky – or about 100 times the size of the full moon. This, in turn, allowed a whole barrage of astronomical telescopes sensitive to light across the entire electromagnetic spectrum to search this small patch of sky for the aftermath of the explosion. And sure enough this was found – in an unfashionable backwater towards the edge of a fairly <a href="https://en.wikipedia.org/wiki/NGC_4993">unassuming galaxy called NGC4993</a>, in the constellation of Hydra. </p>
<p>Over the next few days and weeks astronomers watched agog as the embers from the explosion glowed brightly and faded, beautifully matching the pattern expected for <a href="http://theconversation.com/we-beat-a-cyber-attack-to-see-the-kilonova-glow-from-a-collapsing-pair-of-neutron-stars-85660">a so-called “kilonova”</a>. This is produced when material rich in subatomic particles known as neutrons from the initial merger is ejected at great speed by the gamma ray burst. This ploughs into the surrounding region of space, triggering the production of heavy radioactive elements. </p>
<p>These unstable elements typically split up (decay) to a stable state by emitting radiation. This is what causes the glow of the kilonova, which we have now confirmed by mapping it out in exquisite detail. Our observations also strongly support the theory that the stable end-products of these chains of reactions include copious amounts of precious metals like gold and platinum. While we’ve suspected neutron stars to be key to <a href="https://www.smithsonianmag.com/science-nature/all-the-gold-in-the-universe-could-come-from-the-collisions-of-neutron-stars-13474145/">producing these elements in space</a>, that hypothesis now looks a whole lot more convincing. Indeed, the kilonova that formed from the embers of GW170817 could have produced as much gold as the entire mass of the Earth – that is 1,000 trillion tonnes.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"919936738893602816"}"></div></p>
<p>By observing a kilonova “up close and personal” for the very first time, and seeing how well it fits into the unfolding astronomical storyboard that began with the neutron star merger, astronomers have taken a huge leap forward in our understanding of these violent cosmic events. </p>
<p>The idea that we are all made of stardust is increasingly appreciated in popular culture – in everything from documentaries to song lyrics. But the mind-blowing concept that the gold in our wedding rings and Rolex watches is made of neutron stardust is about to catch on. Perhaps even more exciting, however, is the enormous potential now unlocked by this radical, new approach to studying the cosmos.</p>
<p>By working together collaboratively – using instruments that operate not just across the entire spectrum of light but are sensitive to gravitational waves and even neutrinos too – astronomers are poised to fully open a completely new “multi-messenger” window on the universe, with many further discoveries to be made and cosmic mysteries to be solved. For example, we have already used our observations to make the first ever joint measurement of the expansion rate of the universe, using both gravitational waves and light. Our paper will appear in Nature on October 16.</p>
<p>More results will also surely follow soon. The exciting new era of multi-messenger astronomy just started with a bang.</p><img src="https://counter.theconversation.com/content/85647/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Martin Hendry is a member of the LIGO scientific collaboration.</span></em></p>
The discovery of tiny ripples in space from the violent collision of dense stars could help solve many mysteries – including where the gold in our jewellery comes from.
Martin Hendry, Professor of Gravitational Astrophysics and Cosmology, University of Glasgow
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/85161
2017-10-04T00:42:09Z
2017-10-04T00:42:09Z
How fair is it for just three people to receive the Nobel Prize in physics?
<figure><img src="https://images.theconversation.com/files/188682/original/file-20171003-18916-171bnxd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Alfred Nobel didn't foresee the current era of mega scientific collaboration.</span> <span class="attribution"><a class="source" href="https://www.nobelprize.org/press/#/image-details/584fbf368409c20d00efa01f/552bd85dccc8e20c00e7f979?sh=false">© Nobel Media AB Pi Frisk</a></span></figcaption></figure><p>The Nobel Foundation statutes decree that “<a href="https://www.nobelprize.org/nobel_prizes/facts/">in no case</a>” can a Nobel Prize be divided between more than three people. So it may not raise many eyebrows that the 2017 award in physics went to <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/2017/press.html">just three scientists on the LIGO team</a> for their “decisive contributions to the LIGO detector and the observation of gravitational waves.”</p>
<p>But <a href="https://doi.org/10.1038/497557a">science is increasingly collaborative</a> across teams (including scientists and engineers), across nations and across disciplines. The majority of all scientific articles <a href="https://doi.org/10.1126/science.1136099">are co-authored</a>. Of these, over 25 percent are <a href="https://doi.org/10.1371/journal.pone.0131816">internationally co-authored</a>. LIGO – more than most projects – represents these trends. One of the group’s most important papers involves <a href="https://doi.org/10.1103/PhysRevLett.116.061102">355 co-authors from at least 20 countries</a>.</p>
<p>So with cutting-edge science being carried out in large international collaborations, who actually winds up on the rostrum in Stockholm? As a student of science dynamics, I have tracked how and why scientists link up with one another, in what fields, and how it improves the outcomes. These allegiances have an impact on who receives an award like a Nobel Prize, since international collaborations are more highly cited than national or sole-authored work. </p>
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<a href="https://images.theconversation.com/files/188685/original/file-20171003-739-ejs8rt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/188685/original/file-20171003-739-ejs8rt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/188685/original/file-20171003-739-ejs8rt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/188685/original/file-20171003-739-ejs8rt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/188685/original/file-20171003-739-ejs8rt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/188685/original/file-20171003-739-ejs8rt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/188685/original/file-20171003-739-ejs8rt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/188685/original/file-20171003-739-ejs8rt.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>
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<span class="caption">A LIGO optics technician who is not a recipient of the Nobel Prize.</span>
<span class="attribution"><a class="source" href="https://www.ligo.caltech.edu/image/ligo20151214">Matt Heintze/Caltech/MIT/LIGO Lab</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<h2>Shifting norms around collaboration and credit</h2>
<p>Scientific discoveries these days typically rely on advances in the underlying technology and equipment used in experimentation. To enable breakthroughs, LIGO, CERN, the Human Genome Project and others rely on new technologies, which in turn are built often by large international teams. And within science, it’s becoming standard to more broadly recognize contributions like these than in the past. </p>
<p>This is a shift in social behavior, since scientists have always had collaborators and helpers – they just didn’t grant them a place on the “author” list. Now, there is a greater tendency to list the technical people who make discoveries possible. At CERN, for example, new discoveries, <a href="https://doi.org/10.1103/PhysRevLett.114.191803">such as the Higgs Boson</a>, are claimed in articles that list engineers and computer scientists as well as the theorists who develop the experiments.</p>
<p>And the fact that the Nobel Prize is offered specifically for physics is out of step with the tendency for interdisciplinary contributions to be fundamental to breakthroughs. A quick glance at the list of <a href="https://doi.org/10.1103/PhysRevD.93.042006">contributing institutions for LIGO</a> shows collaborators from a school of mathematics, space science, departments of informatics, as well as cosmologists, astrophysics observatories, supercomputing centers and many others.</p>
<p>While practitioners have expanded the way contributions are credited, awards like the Nobel Prizes haven’t caught up. The little bit of science history taught in school still focuses on individual contributors such as Marie Curie and Albert Einstein. Harder to explain or visualize are the cross-disciplinary collaborations that constitute most of science today.</p>
<h2>The rich get richer</h2>
<p>In a <a href="https://doi.org/10.1371/journal.pone.0134164">study I conducted with the Nobel Library in Sweden</a>, we compared Nobel Prize winners in physiology or medicine to a matched group of scientists to examine productivity, impact, coauthorship and international collaboration patterns. The laureate’s co-author network reveals significant differences from the non-laureate network. Laureates are more likely to build bridges across a network by reaching out to a non-obvious collaborator, such as <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/2000/">physicist Jack Kilby</a> working with a materials scientist to develop new materials for microprocessors. They were more likely to exploit “structural holes” – gaps between fields that offer enticing but unrealized possibilities. </p>
<p>This process builds their reputation within as well as across scientific fields. (For example, both physicists and materials scientists read Kilby’s paper.) In science, reputation is the coin of the realm. It’s gained through cooperation as well as attention to the outputs of science – <a href="http://www.jstor.org/stable/2091085">the journal article</a>.</p>
<p>When publishing any scientific article, there is a basic conundrum – someone must receive the prime place on the list of authors. In some fields, authors covet the first place; in others, the last place. And the benefits of being the primary author go far beyond a single article. There’s a phenomenon called the <a href="https://doi.org/10.1126/science.159.3810.56">“Matthew Effect” in science</a>, referring to the observation in the Gospel of Matthew that the “rich get richer.” The noted author of an article is much more likely to receive attention into the future.</p>
<p>Creative networkers like Jack Kilby grow their network in several fields as a result of their work, enhancing citations and reputation.</p>
<p>Searchable databases such as Google Scholar accentuate the Matthew effect, since a search will prioritize the articles with lots of citations. It has long been noted that <a href="http://www.enid-europe.org/conference/abstract%20pdf/Klavans_Boyack_superstars.pdf">only a few “superstars” in science emerge over time</a> – but current practices have supercharged the process because of the <a href="https://doi.org/10.1073/pnas.98.2.404">agglomerating effects of being listed as the primary author</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/188684/original/file-20171003-18916-1lcaai2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/188684/original/file-20171003-18916-1lcaai2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/188684/original/file-20171003-18916-1lcaai2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/188684/original/file-20171003-18916-1lcaai2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/188684/original/file-20171003-18916-1lcaai2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/188684/original/file-20171003-18916-1lcaai2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/188684/original/file-20171003-18916-1lcaai2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/188684/original/file-20171003-18916-1lcaai2.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">The Nobel stage in Stockholm doesn’t have space for everyone.</span>
<span class="attribution"><a class="source" href="https://www.nobelprize.org/press/#/image-details/585104ccffb1110d00062b3e/552bd85dccc8e20c00e7f979?sh=false">© Nobel Media AB Pi Frisk.</a></span>
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<h2>Who stays behind</h2>
<p>The Matthew Effect is likely part of the reason that three white men came out “on top” in the case of the 2017 Nobel Prize in physics. The downside of needing a primary author on a collaborative paper means that collaborators, such as notable women who also worked on LIGO, sit in the shadows. <a href="https://doi.org/10.1002/asi.1097">Women’s names are much more likely</a> to be listed second, third or farther down the list of authors on scientific papers. It can be difficult for <a href="https://doi.org/10.1371/journal.pbio.2001003">women to claim to top spot</a>.</p>
<p>No doubt when the current Nobel Prize winners in physics accept their award, they will point to “others” who have been instrumental in helping. Yet, the essentially collaborative nature of the work – many paying nations, many collaborating disciplines, a multitude of people – begs the question: Can the award fairly be claimed by three (white, American, male) people? The Nobel Prize, developed to recognize 19th-century creativity, may no longer reflect the true contributions within 21st-century science.</p><img src="https://counter.theconversation.com/content/85161/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Caroline Wagner 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>
Today’s scientific research is characterized by interdisciplinary, international collaboration. Awards like the Nobel Prizes haven’t caught up.
Caroline Wagner, Milton & Roslyn Wolf Chair in International Affairs, The Ohio State University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/66457
2017-10-03T10:12:00Z
2017-10-03T10:12:00Z
Scientists behind the discovery of gravitational waves win the 2017 Nobel Prize for Physics
<figure><img src="https://images.theconversation.com/files/188580/original/file-20171003-30864-3m2a82.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This year's winners</span> <span class="attribution"><span class="source"> Illustration by N. Elmehed. NobelPrize.org</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The Swedish Academy of Sciences <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/2017/press.html">has announced</a> that the 2017 Nobel prize in Physics goes to three scientists for their foundational work leading to the discovery of ripples in the fabric of space and time known as <a href="https://theconversation.com/explainer-gravitational-waves-and-why-their-discovery-is-such-a-big-deal-53239">gravitational waves</a>. </p>
<p>Half of the £825,000 prize sum will go to <a href="http://web.mit.edu/physics/people/faculty/weiss_rainer.html">Rainer Weiss</a> of Massachusetts Institute of Technology, and the other half will be be shared by <a href="https://www.its.caltech.edu/%7Ekip/index.html/">Kip Thorne</a> of Caltech and <a href="https://labcit.ligo.caltech.edu/%7EBCBAct/">Barry C Barish</a>, also at Caltech. The scientists, all from the LIGO/VIRGO collaboration, conceived and played major roles in realising the Laser Interferometer Gravitational-Wave Observatory, which first detected the waves in September 2015. I’m pleased to see this achievement recognised on behalf of the thousands of scientists who work on LIGO, including <a href="https://www.shef.ac.uk/physics/research/pppa/gwrg">the University of Sheffield group</a>. I also know the recipients personally, in particular Weiss, who is a friend as well as a colleague.</p>
<p>Gravitational waves, predicted by Einstein in 1916, travel across our universe at the speed of light – stretching space in one direction and shrinking it in the direction that is at right angles. LIGO <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">measures these fluctuations</a> by monitoring two light beams travelling between pairs of mirrors down pipes running in different directions. </p>
<p>The source of the first detected signals was a pair of black holes, each being about 30 times the mass of the sun. These bodies once collided and converted in to one large spinning black hole – emitting three sun masses worth of pure energy in about a tenth of a second. For that short time, the source outshines the rest of the energy sources in the observable universe – combined! It’s quite something to try and imagine. Despite being such a violent event, it is so far away that the effects on our local fabric of space and time here on Earth are very subtle – which is why a sophisticated detector like LIGO was needed to make the first detection.</p>
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<img alt="" src="https://images.theconversation.com/files/140280/original/image-20161004-20228-1v5siz3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140280/original/image-20161004-20228-1v5siz3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=598&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140280/original/image-20161004-20228-1v5siz3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=598&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140280/original/image-20161004-20228-1v5siz3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=598&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140280/original/image-20161004-20228-1v5siz3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=751&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140280/original/image-20161004-20228-1v5siz3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=751&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140280/original/image-20161004-20228-1v5siz3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=751&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Aerial view of the facility.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/23925401@N06/24342686634">Kanijoman/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p>Several more binary black hole signals have been detected by the LIGO detectors since, and one announced just days ago was detected by the Virgo detector in Italy as well. Now that we know these signals exist and can be detected, a new field of gravitational wave astronomy will grow up, enabling us to probe the dark and puzzling universe – phenomena in the cosmos that don’t emit much light but have a lot of mass. It’s an exciting time.</p>
<h2>Unconventional, sharp and fun</h2>
<p>Those of us at LIGO who know Weiss will agree he is an unconventional fellow in the best sense of that description who has inspired a generation of experimental physicists, myself included. </p>
<p>The first time I met Weiss properly was when he interviewed me for my first postdoc, at MIT. I was in my only smart suit, he walked in wearing a woolly hat, baggy sweater and jeans. I had to reassure him that this was the last time he’d see me dressed up that way. He looked relieved. </p>
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<img alt="" src="https://images.theconversation.com/files/188562/original/file-20171003-12163-gttxkz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/188562/original/file-20171003-12163-gttxkz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=535&fit=crop&dpr=1 600w, https://images.theconversation.com/files/188562/original/file-20171003-12163-gttxkz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=535&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/188562/original/file-20171003-12163-gttxkz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=535&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/188562/original/file-20171003-12163-gttxkz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=672&fit=crop&dpr=1 754w, https://images.theconversation.com/files/188562/original/file-20171003-12163-gttxkz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=672&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/188562/original/file-20171003-12163-gttxkz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=672&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Rainer Weiss.</span>
<span class="attribution"><span class="source">Michael Hauser/wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p>Weiss has a refreshingly informal approach to physics, which is particularly helpful in encouraging others in their work, especially the young. But this informality and enthusiasm only just conceals his razor-sharp instinct for physics, particularly for sources of background noise and for electronics. </p>
<p>And, because he is what I would call “scientifically sociable”, Weiss naturally tends to learn things quickly by talking to people. When I was working at the LIGO lab at Livingston, I did an early systematic comparison of seismic noise between the two LIGO sites in a key frequency range. The tough thing back then was just gathering enough data from the seismometers to be able to make a meaningful comparison between the noise levels. </p>
<p>I’d just made a graph of the results, and I was in the control room staring at it when Weiss walked in. He walked out a few minutes later with a copy of that plot, and the next thing I knew, he was using it in talks to the National Science Foundation when arguing for an upgrade to LIGO Livingston’s seismic isolation system. That’s Weiss in a nutshell. He’s quick on the uptake, good at spotting the key points and problems, and authoritative enough to get others – physicists, engineers and funders on his side. </p>
<p>We also share a love of music. Once when I was invited to dinner at his house, I was asked to bring my cello and had to sight-read several cello sonata movements (rather shakily) with Weiss at the piano. He also showed up to a particularly memorable “hoodoo party night” at a club called Tabby’s blues box in Baton Rouge, Louisiana, where I was playing in a band. He brought along Gaby Gonzalez, who until recently was chairperson of the LIGO scientific collaboration and Peter Saulson, a professor of physics and thermal noise pioneer from Syracuse. A more unlikely crowd on the dance floor at Tabby’s has probably not been seen before or since. They had a great time.</p>
<p>The future of gravitational wave physics is now intimately tied up with the future of astronomy. The field is set to expand rapidly, with more sensitive instruments needed to sense smaller signals and larger scale instruments needed to probe lower frequencies where many of the astronomical signals lie. We also need observers of the heavens, both to interpret the signals we measure, and to make the link between gravitational waves and other sources of information, such as gamma ray and neutrino bursts, and visible transients. We are hoping to continue to play an important role in the research here at Sheffield.</p>
<p>But, for now, it’s time to enjoy the moment of a very well deserved Nobel prize for a great group of physicists. They have played a long game; the project started in 1972, and I didn’t even join until 1997. It’s a lesson to us all to keep both eyes on the science, to be prepared for a protracted struggle with Mother Nature, but ready in the end to step back and admire the edifice we have constructed, and go on to apply the tools we have created to achieving an ever expanding knowledge of our universe.</p><img src="https://counter.theconversation.com/content/66457/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ed Daw works for the University of Sheffield. He receives funding from the Science and Technology Facilities Council (STFC). </span></em></p>
Razor-sharp, unconventional and fun on the dance floor. A colleague paints a colourful portrait of one of this year’s Nobel Laureates in physics.
Ed Daw, Reader in Physics, University of Sheffield
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/84818
2017-09-28T13:47:54Z
2017-09-28T13:47:54Z
Experiments simultaneously detect gravitational waves – and help open up a new era of astronomy
<figure><img src="https://images.theconversation.com/files/187981/original/file-20170928-1483-3wom96.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Virgo detector in Italy.</span> <span class="attribution"><span class="source">Virgo collaboration.</span></span></figcaption></figure><p>The detection of gravitational waves – ripples in the fabric of space itself – by the <a href="https://www.ligo.caltech.edu/">LIGO collaboration</a> last year has been hailed as <a href="https://theconversation.com/explainer-gravitational-waves-and-why-their-discovery-is-such-a-big-deal-53239">one of the most groundbreaking discoveries</a> of the century. Now three detectors as part of two different experiments in the US and Italy <a href="http://www.bbc.co.uk/news/world-australia-41420188">have simultaneously detected</a> another such burst.</p>
<p>The signal – picked up by the <a href="https://www.ligo.caltech.edu/WA">LIGO detector at Hanford</a>, Washington State, the other <a href="https://www.ligo.caltech.edu/LA">LIGO detector at Livingston</a>, Louisisiana and the <a href="http://public.virgo-gw.eu/language/en/">Virgo detector near Pisa in Italy</a> – came from the merger of two black holes. This is the same kind of event that produced the gravitational waves detected in the previous experiments. So why does it matter?</p>
<p>It’s actually hugely important, because it provides the first corroboration of direct detection of gravitational waves by scientists outside the LIGO collaboration. Importantly, the instrument used by the Virgo team has a different physical design from LIGO. And that’s not all. Detection in three detectors provides more accurate information about the position of the event, which took place 2bn years ago, on the sky.</p>
<p>The better we can locate a source, the more likely it is that we will be able to identify other types of waves emitted in the event. This could be “electromagnetic signals” including light, X-rays, gamma rays (high-energy electromagnetic waves) or radio waves. The difference in detection time between gravitational wave detectors gives a rough indication of where on the sky an event took place. That means that we can turn our optical or X-ray telescopes <a href="https://theconversation.com/how-did-the-odd-black-holes-detected-by-ligo-form-and-can-we-spot-them-in-the-sky-54672">to this particular area</a> to see if we can learn even more about it.</p>
<h2>Bright future</h2>
<p>The discovery opens up a new era of astronomy, in which we can investigate different types of waves to study the same events in the cosmos. For example, there are <a href="https://arxiv.org/abs/1602.04735">theories that suggest</a> that two merging holes can produce a burst of gamma rays if they form and merge in a certain way. That can now be tested.</p>
<p>Telescope observations helping us to pinpoint a more exact location of a source of gravitational waves can also help us measure critical parameters of astrophysics such as how fast the universe is expanding and the compositions of objects such as neutron star. They will also enable precision tests of Einstein’s theory of general relativity. In fact, there is a vast amount of science that can be probed by doing astronomy using multiple kinds of waves. This has been dubbed “<a href="https://arxiv.org/abs/1606.09335">multi-messenger astronomy</a>”.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/187982/original/file-20170928-8391-hsp1bu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/187982/original/file-20170928-8391-hsp1bu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/187982/original/file-20170928-8391-hsp1bu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/187982/original/file-20170928-8391-hsp1bu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/187982/original/file-20170928-8391-hsp1bu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/187982/original/file-20170928-8391-hsp1bu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/187982/original/file-20170928-8391-hsp1bu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Black hole collision and merger releasing gravitational waves.</span>
<span class="attribution"><span class="source">Simulating eXtreme Spacetimes/wikimedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>We also expect to soon be able to detect gravitational waves from sources other than black holes – and that could make it much easier to do multi-messenger astronomy. This may be colliding <a href="https://www.space.com/22180-neutron-stars.html">neutron stars</a> (large stars that have collapsed) or <a href="https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-supernova.html">huge star explosions known as supernovas</a>. These are often nearer and emit more light than black holes, meaning they are easier to study with normal telescopes.</p>
<p>Cataclysmic events such as colliding neutron stars can be used as laboratories to study how the universe behaves under extreme conditions that we could never create here on Earth. The information can be used to extend our understanding of the universe, in particular of how it came into existence, and what its future might be. This is the ultimate goal of fundamental science, so the detection of gravitational waves by an increasingly extensive network of observatories is great news for scientists everywhere.</p>
<p>Equally significantly, this event is a tribute to the collaboration of LIGO and Virgo, which could have been bitter rivals in a race to detect gravitational waves, but instead have become close collaborators in a joint venture to understand our universe.</p>
<p>This collaboration extends further towards future gravitational wave detectors in Japan (Kagra) and India (LIGO India) – and out to many astronomy groups working on observing sources that LIGO detects. Indeed it’s an important lesson in the rewards of patience and collaboration, and my own university is proud to be a contributor.</p><img src="https://counter.theconversation.com/content/84818/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ed Daw receives funding from The Science and Technology Facilities Council.
</span></em></p>
New results from Italy and the US help us better estimate the position of the merging black holes that produced the gravitational waves.
Ed Daw, Reader in Physics, University of Sheffield
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/82789
2017-08-23T17:31:53Z
2017-08-23T17:31:53Z
Gravitational waves are helping us crack the mystery of how pairs of black holes form
<figure><img src="https://images.theconversation.com/files/182814/original/file-20170821-4956-1cjwsd0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Black hole collision and merger releasing gravitational waves</span> </figcaption></figure><p>A tiny disturbance in space became an enormous scientific discovery when <a href="https://www.ligo.caltech.edu/">LIGO</a> amazingly managed to register it early on the morning of September 14, 2015. This was the first ever observation of a “gravitational wave” – a minute ripple in the structure of spacetime itself – predicted by Albert Einstein a century ago. The signal came from two black holes merging more than a billion light years away, and reached our planet on that very morning.</p>
<p>The detection ushered in a whole new era of astronomy. Two more detections followed (and a third likely one), all from mergers of pairs of black holes. Already, these measurements are starting to help scientists unravel some of the universe’s best-kept secrets. Our new study, <a href="http://dx.doi.org/10.1038/nature23453">published in Nature</a>, shows just how close we are to working out how pairs of black holes form.</p>
<p>The black holes studied by LIGO – each weighing in at between 10 and 30 times the mass of the sun – collide while moving at half the speed of light, twisting space and time as they do so. The merger of two black holes releases more energy in a fraction of a second than all of the stars in the visible universe combined. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/182816/original/file-20170821-4964-1nfl0b0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/182816/original/file-20170821-4964-1nfl0b0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=598&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182816/original/file-20170821-4964-1nfl0b0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=598&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182816/original/file-20170821-4964-1nfl0b0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=598&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182816/original/file-20170821-4964-1nfl0b0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=751&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182816/original/file-20170821-4964-1nfl0b0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=751&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182816/original/file-20170821-4964-1nfl0b0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=751&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">LIGO in Louisina.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/23925401@N06/24342686634">Kanijoman/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>However, by the time the spacetime distortions, travelling at the speed of light for more than a billion years, get to the Earth, the ripples are very weak indeed – stretching and squeezing space by less than one part in 10<sup>21</sup>. That means they make the mirrors in the LIGO detector move by less than a thousandth of the size of an atomic nucleus. No wonder gravitational waves have been so hard to detect.</p>
<h2>The incomplete science of black holes</h2>
<p>Black holes are infinitely dense remnants of massive stars. Studying them provides astrophysicists with a glimpse into the lives of these stars. And one of the key questions puzzling us since the first gravitational wave detection is: how did these heavy black hole pairs get close enough to merge? </p>
<p>Unravelling the history of how merging black holes formed is important – it can help us to understand the mysterious ageing of massive stars and interactions in dense stellar environments. </p>
<p>There are <a href="https://www.nature.com/nature/journal/v547/n7663/pdf/547284a.pdf">two broad classes of scenarios</a> that have been proposed so far. The first view holds that two massive stars were born as a pair. They may have interacted by raising tides on each other’s surface, in the way that the moon raises ocean tides on the Earth. Or they <a href="https://www.space.com/22509-binary-stars.html">may have exchanged gas</a>, with one star blowing off material into space and the other capturing some of it. </p>
<p>Eventually, each star collapsed into a black hole. If the black holes were close enough, then the gradual loss of energy from their orbits in the form of gravitational waves would cause the two black holes to spiral in and eventually merge. This scenario is known as isolated binary evolution. </p>
<p>The other option is that the two black holes formed independently, but did so in an environment where there were many stars closely packed together. In this scenario, known as dynamical formation, a sequence of gravitational interactions with other stars could bring the two black holes to orbit each other.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/183106/original/file-20170823-13293-1ar20iw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/183106/original/file-20170823-13293-1ar20iw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=462&fit=crop&dpr=1 600w, https://images.theconversation.com/files/183106/original/file-20170823-13293-1ar20iw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=462&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/183106/original/file-20170823-13293-1ar20iw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=462&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/183106/original/file-20170823-13293-1ar20iw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=581&fit=crop&dpr=1 754w, https://images.theconversation.com/files/183106/original/file-20170823-13293-1ar20iw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=581&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/183106/original/file-20170823-13293-1ar20iw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=581&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Numerical simulations of the gravitational waves emitted by the merger of two black holes, including spins (green arrow).</span>
<span class="attribution"><span class="source">NASA/wikipedia</span></span>
</figcaption>
</figure>
<p>We do not yet know which scenario is correct, but nature has provided an exciting hint. Black holes rotate around their own axes. We know from a few observations of stars orbiting black holes in our own galaxy and its immediate neighbours that sometimes black holes appear to be rapidly spinning. We think that if the black holes seen by LIGO were formed from stars already orbiting each other, these spins should be aligned with the orbit. But if the black holes formed by the gravitational influence of several other stars, the spins would be randomly oriented relative to the orbit – meaning they formed independently in a dense environment. </p>
<p>In a new paper, our team of scientists from the University of Birmingham in the UK and the Universities of Maryland and Chicago in the US, analysed the alignment of the spins and orbits of the merging black hole pairs detected by LIGO. It turns out that the phase of the gravitational waves measured is influenced by the spin of the black holes. A certain component of this spin – known as effective spin – is therefore imprinted in the data. </p>
<p>If this effective spin is large and positive, the black holes are rapidly spinning and rotating in the same direction as the orbit. If it’s large and negative, the black holes are rapidly counter-rotating with respect to the orbit. If it is near zero, then either the black holes’ spins are significantly misaligned with the orbit, or both black holes are spinning slowly.</p>
<p>The LIGO observations of merging black holes so far have found that the effective spin is consistent with zero for all but one observation. Therefore, we concluded that if the black holes are rapidly spinning, the data point to a lack of alignment – and that the black holes were not born from pairs of stars. It does indeed seem likely that the black holes could be rapidly spinning – observations in our galaxy after all suggest this is the case.</p>
<p>We suggest that with as few as ten additional detections, it may be possible to know for sure the origin of black hole pairs. However, it is possible that the merging black holes had a different evolutionary history to the black holes we’ve observed in our own galaxy, and are rotating slowly. If they are, many more observations would be required. Either way, the research goes to show just how important the discovery of gravitational waves really is – opening an entirely new window on the universe.</p><img src="https://counter.theconversation.com/content/82789/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ilya Mandel receives funding from STFC, and acknowledges support from the National Science Foundation under Grant No. NSF PHY11-25915. </span></em></p>
New research shows that as few as ten further detections of gravitational waves will help scientists know for sure how pairs of black holes form.
Ilya Mandel, Professor of Theoretical Astrophysics, University of Birmingham
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/78262
2017-06-01T20:12:44Z
2017-06-01T20:12:44Z
A new discovery of gravitational waves has black holes in a spin
<figure><img src="https://images.theconversation.com/files/171751/original/file-20170601-25684-2huty9.png?ixlib=rb-1.1.0&rect=730%2C235%2C2517%2C1730&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A simulation of the latest binary black hole merger detected by LIGO. Blue indicates weak fields and yellow indicates strong fields.</span> <span class="attribution"><span class="source">Numerical-relativistic Simulation: S Ossokine, A Buonanno (Max Planck Institute for Gravitational Physics) and the Simulating eXtreme Spacetime project Scientific Visualization: T Dietrich (Max Planck Institute for Gravitational Physics), R Haas (NCSA)</span></span></figcaption></figure><p>Within just a couple of months of turning back on for its second major science run, the Laser Interferometer Gravitational-wave Observatory (<a href="http://ligo.org/">LIGO</a>) made a third detection of <a href="https://theconversation.com/au/topics/gravitational-waves-9473">gravitational waves</a>, ripples in space and time, demonstrating that a new window in astronomy has been firmly opened.</p>
<p>As was the case with the first two <a href="http://ligo.org/detections/">detections</a>, the waves were generated when two massive black holes merged to form a larger one. </p>
<p>In the latest merger, <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.221101">detailed today in the journal Physical Review Letters</a>, the resulting black hole was about 50 times the mass of our Sun.</p>
<p>The detection is called GW170104 - so named because it was made on January 4 this year. The merging black holes are probably the most distant yet seen, about three billion light-years from Earth. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/171945/original/file-20170602-1275-12n3oq6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/171945/original/file-20170602-1275-12n3oq6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171945/original/file-20170602-1275-12n3oq6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171945/original/file-20170602-1275-12n3oq6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171945/original/file-20170602-1275-12n3oq6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171945/original/file-20170602-1275-12n3oq6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171945/original/file-20170602-1275-12n3oq6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171945/original/file-20170602-1275-12n3oq6.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">Infographic showing the approximate masses and distances to the first three gravitational wave sources discovered by LIGO.</span>
<span class="attribution"><span class="source">ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The three known LIGO events are remarkable for the amount of energy liberated in the final few seconds before the merger. In that time their energy loss rate (luminosity) is greater than all the stars in the observable universe put together.</p>
<p>When you think that there are more than 100 billion stars in our galaxy, and a similar number of galaxies in the universe, you realise the stupendous amount of energy that is released during these mergers.</p>
<p>Despite the energetics of these events, the ripples cause the LIGO mirrors to be displaced by a rather paltry 0.000000000000000001 of a metre. That’s about one-thousandth the size of the nucleus of an atom!</p>
<p>Remarkably, LIGO is capable of measuring such tiny displacements. <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">This technology</a> has been developed over decades.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/mQRoYr15twU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An OzGrav animation depicting the binary black hole merger event GW170104, detected by LIGO. The animation simulates the final moments of the merger and is placed near the Earth as an indication of scale.</span></figcaption>
</figure>
<h2>All in the spin</h2>
<p>The gravitational waves are detected by fitting one of a large number of theoretical “templates” to the data. These templates model how the detectors will react to the passing waves from different mass black holes.</p>
<p>There are two leading models for how these massive black holes are brought together. </p>
<p>In the simplest model, they are born as a stellar pair. Like planets, black holes spin about their axis. Black holes born in a stellar pair are thought to spin in the same direction.</p>
<p>In the other model, massive black holes court each other in huge swarms of stars known as globular clusters. They exchange partners until they dance too close and spiral together in a burst of gravitational waves. </p>
<p>In this model, the two black holes are unlikely to spin in the same direction.</p>
<p>There is some evidence that this latest black hole collision comes from the second class.</p>
<p><a href="http://www.phys.psu.edu/people/bss25">Prof Bangalore Sathyaprakash</a>, of Penn State University, is one of authors of the journal paper. He says:</p>
<blockquote>
<p>This is the first time that we have evidence that the black holes may not be aligned, giving us just a tiny hint that pairs of black holes may form in dense stellar clusters.</p>
</blockquote>
<p>LIGO will continue to be upgraded over the coming years, and the rate of detections is expected to increase as LIGO is further refined with new technologies. With more detections LIGO will be able to further test the stellar cluster hypothesis.</p>
<h2>Australia’s gravitational wave experts</h2>
<p>Members of the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (<a href="http://www.ozgrav.org/">OzGrav</a>) anxiously await these new data. We asked some of OzGrav’s postdocs, students and chief investigators what they were most excited about in this nascent field of astrophysics.</p>
<h3>Susan Scott, Professor of Physics at Australian National University and a chief investigator at OzGrav</h3>
<blockquote>
<p>In the coming years I am eagerly anticipating the detection of continuous gravitational waves radiated by rotating neutron stars with small deformities or minute “mountains”.</p>
<p>With a combination of relativistic velocities, huge magnetic fields and densities beyond that of an atomic nucleus, neutron stars are expected to emit gravitational waves of sufficient amplitude to be detectable by Advanced LIGO. Their detection is a very exciting prospect as it would reveal much about the physics of matter at extreme densities.</p>
</blockquote>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=27&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=27&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=27&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=34&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=34&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=34&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<h3>Letizia Sammut, Postdoctoral Researcher at Monash University</h3>
<blockquote>
<p>One of the most exciting possibilities of gravitational wave astronomy is the detection of gravitational waves from the very early universe almost immediately after the Big Bang!</p>
<p>Observation of such a signal would have far-reaching applications across many fields of physics and over a wide range of (energy and length) scales.</p>
</blockquote>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=27&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=27&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=27&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=34&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=34&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=34&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<h3>Lilli Sun, PhD candidate at the University of Melbourne</h3>
<blockquote>
<p>Neutron stars tell their stories continuously by emitting gravitational waves. Once we hear them humming, we will learn how physics works under extreme conditions which can never be reproduced on Earth, like how matter behaves in the densest stars, how a fluid composed almost entirely of neutrons moves, how incredibly strong magnetic fields twist and tangle and annihilate, and so on.</p>
<p>We cannot “see” these things with our own eyes, but now we may have the chance to “hear” them!</p>
</blockquote>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=27&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=27&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=27&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=34&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=34&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=34&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<h3>David Ottaway, Associate Professor at the University of Adelaide</h3>
<blockquote>
<p>The most exciting thing about the future of gravitational waves is using detectors limited only by quantum mechanics to measure the composition of neutron stars, which are an exotic form of matter that cannot be studied any other way.</p>
</blockquote>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=27&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=27&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=27&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=34&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=34&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=34&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<h3>Bram Slagmolen, ARC Future Fellow at the Australian National University</h3>
<blockquote>
<p>The future of gravitational waves using next-generation detectors will be super exciting. We will not only be able to observe deeper into the universe, at the same time, we will also be able to study fundamental physics in extreme environments more precisely.</p>
</blockquote>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=27&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=27&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=27&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=34&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=34&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171764/original/file-20170601-25673-1wf56lp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=34&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<h3>Qi Chu, Phd student at the University of Western Australia</h3>
<blockquote>
<p>I am part of a team led by Professor Linqing Wen at UWA that is racing to create faster ways to crunch the LIGO data to minimise the time between the gravitational waves hitting earth and an alert being sent for follow-up observations with other telescopes.</p>
<p>That will help us localise the event to a host galaxy to learn even more about these extreme events in the universe.</p>
</blockquote><img src="https://counter.theconversation.com/content/78262/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Bailes receives funding from the Australian Research Council to undertake fundamental research in astrophysics.
</span></em></p><p class="fine-print"><em><span>Eric Thrane receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Paul Lasky receives funding from the Australian Research Council. </span></em></p>
Scientists have made a third detection of gravitational waves, again caused by the merger of two black holes. But they think there’s something different about the black holes in this case.
Matthew Bailes, ARC Laureate Fellow, Swinburne University of Technology., Swinburne University of Technology
Eric Thrane, Senior Lecturer in Physics & Astronomy, ARC Future Fellow, Node Leader, ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), Monash University
Paul Lasky, Lecturer and ARC Future Fellow, Monash University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/78571
2017-06-01T16:41:34Z
2017-06-01T16:41:34Z
LIGO detects more gravitational waves, from even more ancient and distant black hole collisions
<figure><img src="https://images.theconversation.com/files/171733/original/file-20170531-25676-1n7a6j4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's conception of two merging black holes, spinning in a nonaligned fashion.</span> <span class="attribution"><span class="source">LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>For the third time in a year and a half, the Advanced Laser Interferometer Gravitational Wave Observatory <a href="https://doi.org/10.1103/PhysRevLett.118.221101">has detected gravitational waves</a>. Hypothesized by Einstein a century ago, the <a href="https://theconversation.com/what-happens-when-ligo-texts-you-to-say-its-detected-one-of-einsteins-predicted-gravitational-waves-53259">identification of these ripples in space-time</a> – for the third time, no less – is fulfilling the promise of an area of astronomy that has enticed scientists for decades, but had always seemed to lie just out of our reach.</p>
<p>As a gravitational-wave astrophysicist and member of the <a href="http://www.ligo.org">LIGO Scientific Collaboration</a>, I am naturally thrilled to see the vision of so many of us becoming a reality. But I’m accustomed to finding my own work more interesting and exciting than other people do, so the extent to which the whole world seems to be fascinated by this accomplishment came as something of a surprise. The excitement is well-deserved, though. By <a href="https://doi.org/10.1103/PhysRevLett.116.061102">detecting these gravitational waves</a> for the first time, we’ve not only directly verified a key prediction of Einstein’s theory of general relativity in convincing and spectacular fashion, but we’ve opened up an entirely new window that will revolutionize our understanding of the cosmos.</p>
<p>Already these discoveries have affected our understanding of the universe. And LIGO is just getting started.</p>
<h2>Tuning in to the universe</h2>
<p>At its core, this new way of understanding the universe stems from our newfound ability to hear its soundtrack. Gravitational waves aren’t actually sound waves, but the analogy is apt. Both types of waves carry information in a similar way, and both are completely independent phenomena from light. </p>
<p>Gravitational waves are ripples in space-time that propagate outward from intensely violent and energetic processes in space. They can be generated by objects that don’t shine, and they can travel through dust, matter or anything else, without being absorbed or distorted. They carry unique information about their sources that reaches us in a pristine state, giving us a true sense of the source that can’t be obtained in any other way. </p>
<p>General relativity tells us, among other things, that some stars can become so dense that they close themselves off from the rest of the universe. These extraordinary objects are called black holes. General relativity also predicted that when pairs of black holes orbit tightly around each other in a binary system, they stir up space-time, the very fabric of the cosmos. It’s this disturbance of space-time that sends energy across the universe in the form of gravitational waves.</p>
<p>That loss of energy causes the binary to tighten further, until eventually the two black holes smash together and form a single black hole. This spectacular collision generates more power in gravitational waves than is radiated as light by all the stars in the universe combined. These catastrophic events last only tens of milliseconds, but during that time, they are the most powerful phenomena since the Big Bang.</p>
<p>These waves carry information about the black holes that can’t possibly be gained in any other way, since telescopes can’t see objects that don’t emit light. For each event, we are able to measure the black holes’ masses, their rate of rotation or “spin,” and details about their locations and orientations with varying degrees of certainty. This information allows us to learn how these objects were formed and evolved across cosmic time. </p>
<p>While we have previously had strong evidence for the existence of black holes <a href="https://en.m.wikipedia.org/wiki/Sagittarius_A*">based on the effect of their gravity on surrounding stars and gas</a>, the detailed information from gravitational waves is invaluable for learning about the origins of these spectacular events.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/171743/original/file-20170601-25676-195envm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/171743/original/file-20170601-25676-195envm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171743/original/file-20170601-25676-195envm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171743/original/file-20170601-25676-195envm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171743/original/file-20170601-25676-195envm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171743/original/file-20170601-25676-195envm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171743/original/file-20170601-25676-195envm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171743/original/file-20170601-25676-195envm.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">Aerial view of the LIGO gravitational wave detector in Livingston, Louisiana.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/pennstatelive/26661493514">LIGO</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Detecting the tiniest fluctuations</h2>
<p>In order to detect these incredibly quiet signals, researchers constructed two LIGO instruments, one in <a href="https://www.ligo.caltech.edu/WA">Hanford, Washington</a> and the other 3,000 miles away in <a href="https://www.ligo.caltech.edu/LA">Livingston, Louisiana</a>. They’re designed to leverage the unique effect that gravitational waves have on whatever they encounter. When gravitational waves pass by, they change the distance between objects. There are gravitational waves going through you right now, forcing your head, feet and everything in between to move back and forth in a predictable – but imperceptible – way.</p>
<p>You can’t feel this effect, or even see it with a microscope, because the change is so incredibly tiny. The gravitational waves that we can detect with LIGO change the distance between each end of the 4-kilometer-long detectors by only 10⁻¹⁸ meters. How small is this? A thousand times smaller than the size of a proton – which is why we can’t expect to see it even with a microscope.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/171742/original/file-20170601-23531-1dsgmm5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/171742/original/file-20170601-23531-1dsgmm5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/171742/original/file-20170601-23531-1dsgmm5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=792&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171742/original/file-20170601-23531-1dsgmm5.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=792&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171742/original/file-20170601-23531-1dsgmm5.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=792&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171742/original/file-20170601-23531-1dsgmm5.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=995&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171742/original/file-20170601-23531-1dsgmm5.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=995&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171742/original/file-20170601-23531-1dsgmm5.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=995&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 scientists working on its optics suspension.</span>
<span class="attribution"><span class="source">LIGO Laboratory</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>To measure such a minute distance, <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">LIGO uses a technique called “interferometry.”</a> Researchers split the light from a single laser into two parts. Each part then travels down one of two perpendicular arms that are each 2.5 miles long. Finally, the two join back together and are allowed to interfere with each other. The instrument is carefully calibrated so that, in the absence of a gravitational wave, the interference of the laser results in nearly perfect cancellation – no light comes out of the interferometer.</p>
<p>However, a passing gravitational wave will stretch one arm at the same time as it squeezes the other arm. With the relative lengths of the arms changed, the interference of the laser light will no longer be perfect. It’s this tiny change in the amount of interference that Advanced LIGO is actually measuring, and that measurement tells us what the detailed shape of the passing gravitational wave must be. </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>All gravitational waves have the shape of a “chirp,” where both the amplitude (akin to the loudness) and the frequency, or pitch, of the signals increase with time. However, the characteristics of the source are encoded in the precise details of this chirp and how it evolves with time.</p>
<p>The shape of the gravitational waves that we observe, in turn, can tell us details about the source that could not be measured in any other way. With the first three confident detections by Advanced LIGO, we’ve already found that black holes are more common than we ever expected, and that the most common variety, which forms directly from the collapse of massive stars, can be more massive than we previously thought was possible. All this information helps us understand how massive stars evolve and die. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/171739/original/file-20170601-23531-85y4rx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/171739/original/file-20170601-23531-85y4rx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171739/original/file-20170601-23531-85y4rx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=415&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171739/original/file-20170601-23531-85y4rx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=415&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171739/original/file-20170601-23531-85y4rx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=415&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171739/original/file-20170601-23531-85y4rx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=522&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171739/original/file-20170601-23531-85y4rx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=522&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171739/original/file-20170601-23531-85y4rx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=522&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 three confirmed detections by LIGO (GW150914, GW151226, GW170104), and one lower-confidence detection (LVT151012), point to a population of stellar-mass binary black holes that, once merged, are larger than 20 solar masses – larger than what was known before.</span>
<span class="attribution"><span class="source">LIGO/Caltech/Sonoma State (Aurore Simonnet)</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Black holes becoming less of a black box</h2>
<p>This most recent event, which we detected on Jan. 4, 2017, is the most distant source we’ve observed so far. Because gravitational waves travel at the speed of light, when we look at very distant objects, we also look back in time. This most recent event is also the most ancient gravitational wave source we’ve detected so far, having occurred over two billion years ago. Back then, the universe itself was 20 percent smaller than it is today, and multicellular life had not yet arisen on Earth.</p>
<p>The mass of the final black hole left behind after this most recent collision is 50 times the mass of our sun. Prior to the first detected event, which weighed in at 60 times the mass of the sun, astronomers didn’t think such massive black holes could be formed in this way. While the second event was only 20 solar masses, detecting this additional very massive event suggests that such systems not only exist, but may be relatively common.</p>
<p>In addition to their masses, black holes can also rotate, and their spins affect the shape of their gravitational-wave emission. The effects of spin are more difficult to measure, but this most recent event shows evidence not only for spin, but potentially for spin that is not oriented around the same axis as the binary’s orbit. If the case for such misalignment can be made stronger by observing future events, it will have significant implications for our understanding of how these black hole pairs form.</p>
<p>In the coming years, we will have more instruments like LIGO listening for gravitational waves in <a href="http://public.virgo-gw.eu/language/en/">Italy</a>, in <a href="http://gwcenter.icrr.u-tokyo.ac.jp/en/">Japan</a> and in <a href="http://www.gw-indigo.org/tiki-index.php?page=LIGO-India">India</a>, learning even more about these sources. My colleagues and I are still eagerly awaiting the first detection of a binary containing at least one <a href="https://theconversation.com/explainer-what-is-a-neutron-star-29341">neutron star</a> – a type of dense star that was not quite massive enough to collapse all the way to a black hole.</p>
<p>Most astronomers predicted that pairs of neutron stars would be observed before black-hole pairs, so their continued absence would present a challenge to theorists. Their eventual detection will facilitate a host of new possibilities for discoveries, including the prospect of better understanding extremely dense states of matter, and potentially observing a unique light signature using conventional telescopes from the same source as the gravitational-wave signal.</p>
<p>We also expect to detect gravitational waves within the next few years from space, using very precise natural clocks called pulsars, which send <a href="https://en.wikipedia.org/wiki/Pulsar_timing_array">blasts of radiation our way at very regular intervals</a>. Eventually <a href="https://lisa.nasa.gov">we plan to place</a> <a href="https://www.elisascience.org">extremely large interferometers in orbit</a>, where they can evade the persistent rumbling of the Earth, which is a limiting source of noise for the Advanced LIGO detectors.</p>
<p>Nearly every time scientists have built new telescopes or particle accelerators, they’ve discovered things no one could have predicted. As exciting as the known prospects for discovery are in this new field of gravitational-wave astrophysics, as a theorist I’m most excited by the unknown wonders that still lie in store for us.</p><img src="https://counter.theconversation.com/content/78571/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sean McWilliams is a member of the LIGO Scientific Collaboration, and receives funding from the National Science Foundation. </span></em></p>
These ripples in the very fabric of the universe were hypothesized by Einstein a century ago. Now scientists have detected them for the third time in a year and a half – ushering in a new era in astrophysics.
Sean McWilliams, Assistant Professor of Physics and Astronomy, West Virginia University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/65156
2016-09-12T20:14:20Z
2016-09-12T20:14:20Z
Australia to embrace the new era of gravitational wave astronomy
<figure><img src="https://images.theconversation.com/files/137313/original/image-20160912-13371-1aua029.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Gravitational waves are produced by some of the most extreme events in the universe.</span> <span class="attribution"><span class="source">NASA/SXS Lensing</span></span></figcaption></figure><p>Four hundred years ago Galileo pointed a telescope at Jupiter and saw <a href="http://www.historytoday.com/richard-cavendish/galileo-observes-satellites-jupiter">electromagnetic waves (light) being reflected off its moons</a>. </p>
<p>This profound observation displaced Earth from its position at the centre of the universe to just one planet among many. It also sparked a new golden era of optical astronomy, which <a href="https://theconversation.com/au/topics/hubble-space-telescope-847">continues to this day</a>.</p>
<p>In September 2015 the Advanced Laser Interferometer Gravitational-Wave Observatory (<a href="https://theconversation.com/au/topics/ligo-24713">aLIGO</a>) detected the gravitational waves emitted by two coalescing black holes. This remarkable discovery opened up a new window on the universe, using gravitational waves rather than electromagnetic waves to peer into the far reaches of the cosmos.</p>
<p>A little before aLIGO’s successful detection, I was invited to put together a team to bid for an Australian Research Council Centre of Excellence for Gravitational Wave Discovery, to be known as “OzGRav”. </p>
<p>Centres of Excellence are a scientist’s idea of funding nirvana because they provide guaranteed funding for seven years. So instead of writing annual grant applications with a <a href="http://www.arc.gov.au/rms-funding-announcements-web-page">slim chance</a> of success of getting a fraction of what you asked for, you can plan and execute a serious scientific agenda with critical mass. </p>
<p>But the competition is fierce, and the chances of success are small, and funding rounds are only held every three years or so. To be successful, Centres need bold visions and ambitious objectives.</p>
<p>Our main problem when we submitted our pitch was that no-one had detected gravitational waves yet, and we were relying on the promise of new instruments like aLIGO to deliver in an area that was still void of positive results. </p>
<p>But unbeknown to any of us, the enormous burst of gravitational waves from GW150914 was <em>en route</em> to Earth and due to strike it just two months after our initial application was submitted. </p>
<p>The gravitational waves were generated more than a billion years ago when two enormous <a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">black holes merged</a> after a death spiral. And shortly after the aLIGO gravitational wave detector was turned on it saw the characteristic “chirp” as space time shook during its passage.</p>
<p>Many of my OzGRav team had aided in the construction of aLIGO, and its precision is mind-blowing. When the first source of gravitational waves ever detected (GW150914) were impacting the four kilometre long arms of the detector, they shook by the equivalent of less than the width of a human hair at the distance of the nearest star!</p>
<p>So when our grant was being assessed, gravitational waves were still just a twinkle in the scientific community’s eye. One of our assessors even made it very clear that physicists were always promising to detect gravitational waves but none had been found.</p>
<p>With some luck we were selected to submit a full proposal; one of only 20 teams to do so. </p>
<p>By this time, many of my collaborators were fully aware that the first gravitational waves had been discovered. But they were bound by the strict rules of the LIGO Scientific Consortium that prohibited them from telling me (the proposed Director of the Centre) or putting this news in our proposal, or the rejoinder. It must have been killing them.</p>
<p>All we could say was the data were looking really exciting!</p>
<p>Fortunately for us, the discovery of gravitational waves was announced just prior to the interviews of the final 20 Centre of Excellence teams, and many of my team were invited to parliament house to describe their role in the discovery.</p>
<p>Last week we heard that we were one of the <a href="http://www.arc.gov.au/selection-report-arc-centres-excellence-funding-commencing-2017">nine Centres fortunate enough to gain funding</a>. I’m certain this is at least partly attributable to the fact that a billion years ago in a galaxy far, far away, two black holes, some 30 times the mass of our sun tore each other apart, releasing gravitational waves in the process.</p>
<p>The impact of this discovery has been remarkable. In only six months the discovery paper has already gathered 641 citations. <a href="https://theconversation.com/second-detection-heralds-the-era-of-gravitational-wave-astronomy-61080">Another black hole merger</a> event was published by the LIGO consortium in June and the (now) “telescope” is gearing up for its second major run after some tweaks to its hardware that seems certain to discover more events.</p>
<h2>Our role</h2>
<p>OzGRav has three major themes that will be driving its research programmes: instrumentation, data and astrophysics. </p>
<p>The instrumentation behind these gravitational wave detectors is truly remarkable. OzGRav scientists will aid in the enhancement of aLIGO so that it is even more sensitive, using amazing tricks such as quantum squeezing. We will also help design and ultimately construct the next-generation detectors that aim to detect thousands of events per year. </p>
<p>To minimise the possible locations of these events, it would also make a lot of sense to build one of these new detectors in Australia.</p>
<p>But aLIGO isn’t the only detector capable of discovering gravitational waves. Radio astronomers can use neutron stars (pulsars) that rotate many hundreds of times per second to sense “disturbances in the space-time continuum” induced by the gravitational waves coming from super-massive black holes.</p>
<p>OzGRav engineers are currently designing the supercomputers that will monitor dozens of these stars using the <a href="https://theconversation.com/au/topics/square-kilometre-array-168">Square Kilometre Array</a>. The CSIRO’s Parkes telescope is also having a powerful new receiver fitted to continue its leading role in this area of science.</p>
<p>Swinburne University of Technology will host the Centre headquarters and design a supercomputer custom-built to process the data coming from the gravitational wave detectors. </p>
<p>These data will be processed to look for not just merging black holes, but also neutron stars. And the closest neutron stars will be monitored to see if tiny “magnetic mountains” on their surfaces cause them to generate detectable gravitational wave emission.</p>
<p>OzGRav’s astronomers will also use a network of telescopes at traditional frequencies (optical and radio) to search for evidence of gravitational wave events at other wavelengths to help identify the host galaxies (or lack thereof?) to help understand where the sources of gravitational waves come from. </p>
<p>Finally, our astrophysicists will attempt to explain what our detectors see, and whether Einstein’s theory of <a href="https://theconversation.com/au/topics/general-relativity-161">general relativity</a> is correct or needs some tweaks.</p>
<p>Fortunately Australian scientists can fully engage with this new window on the universe and participate in the first decade of this exciting new era of gravitational wave astrophysics thanks to the Australian Research Council’s Centre of Excellence programme.</p><img src="https://counter.theconversation.com/content/65156/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Bailes works for Swinburne University of Technology, the host of OzGRav. He receives funding from the Australian Research Council.</span></em></p>
The OzGRav Centre of Excellence for Gravitational Wave Discovery will enable Australian researchers to be at the forefront of gravitational wave astronomy.
Matthew Bailes, ARC Laureate Fellow, Swinburne University of Technology., Swinburne University of Technology
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/61080
2016-06-16T01:05:26Z
2016-06-16T01:05:26Z
Second detection heralds the era of gravitational wave astronomy
<figure><img src="https://images.theconversation.com/files/126827/original/image-20160615-19900-yvudeu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An illustration showing the merger of two black holes and the gravitational waves that ripple outward.</span> <span class="attribution"><span class="source">LIGO/T. Pyle</span></span></figcaption></figure><p>Earlier this year, a team of over 1,000 scientists from across the globe announced the <a href="https://theconversation.com/gravitational-waves-discovered-scientists-explain-why-it-is-such-a-big-deal-54521">first discovery of gravitational waves</a> and the first ever observation of colliding black holes.</p>
<p>That same team has now <a href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.241103">published</a> a second gravitational-wave observation from another cataclysmic black hole death spiral, detected on Boxing Day, December 26, 2015. But what is the significance of this second discovery, and what’s its impact on astronomy?</p>
<p>Predicted by Albert Einstein, gravitational waves are tiny ripples in the fabric of spacetime caused by very heavy objects accelerating at very high speeds. The first detection of gravitational waves by the <a href="http://www.ligo.org">LIGO Scientific Collaboration</a> came from two black holes, each weighing about 30 times more than our sun, and travelling at approximately 60% the speed of light just prior to their collision. </p>
<p>This new system is similar to the first. The black holes that announced their merger on Boxing Day each weighed about ten times more than the sun. The catastrophic collision occurred more than a billion light years from Earth, and released one solar mass of energy in gravitational waves.</p>
<p>That is, the amount of gravitational-wave energy released during the merger was equivalent to obliterating the sun, and converting it into pure energy. Darth Vader’s Death Star doesn’t even compare!</p>
<p>Remarkably, this humongous amount of energy only caused the LIGO detectors to wobble by less than one thousandth the size of the nucleus of an atom.</p>
<h2>Black holes are abundant</h2>
<p>The observation of a second black hole merger implies there are many more black holes in the universe than most scientists had previously anticipated.</p>
<p>The uncertainty in the black hole merger rate is very large when you just have a single event, so we now know that we just didn’t “get lucky” with the first detection. </p>
<p>There are going to be a lot of them. This is fantastic news for gravitational-wave astronomers. </p>
<p>First and foremost, it tells us that the future of gravitational-wave astronomy will be rich with scientific discoveries. Calculations suggest that we are likely to detect tens to hundreds of black hole mergers in the next two to three years, and thousands of mergers in the years to follow. </p>
<p>Ongoing technological advancements will continue to enhance the instrument’s sensitivity. Planned technology upgrades will enable us to see these mergers to greater distances, increasing the detection rate by a factor of about 30.</p>
<p>But technology development will not stop there. Teams around the globe, including in Australia, are already working on next-generation technology to be implemented in future LIGO upgrades, resulting in even more detections.</p>
<h2>More black holes than you can poke a stick at</h2>
<p>Are we just being greedy? Now that we’ve observed two black hole mergers, what more could we want?</p>
<p>Well, it turns out that these first observations have raised as many questions as they’ve answered. Some questions we can only begin to attack by studying large populations of black hole mergers.</p>
<p>For example, we don’t know how these systems form. It could be that both black holes are born separately in giant supernova explosions, and then find one another as they embark upon their cosmic wander in dense clusters of stars.</p>
<p>Alternatively they could be born together in binary star systems. This currently open question could be answered once we have seen enough mergers.</p>
<p>Another exciting possibility is to use black holes to study the evolution of the universe as whole. When Australia’s Brian Schmidt and colleagues won the Nobel Prize for showing that the expansion of the universe is accelerating, they did so using observations of supernovae in the distant universe.</p>
<p>Observations of populations of merging black holes with future instruments will be able to measure the expansion of the universe with unprecedented accuracy.</p>
<p>And if these potential discoveries aren’t exciting enough, it turns out that spacetime has memory. </p>
<p>After a gravitational wave passes, spacetime is permanently deformed. That is, the distance between any two objects does not return to its original length – your body is permanently squeezed and stretched after the passage of a gravitational wave.</p>
<p><a href="https://astrobites.org/2016/05/21/detecting-gravitational-wave-memory/">New calculations</a> show that it will be possible to measure memory using future LIGO observations. </p>
<p>Before the first gravitational-wave discovery, we had never tested Einstein’s relativity using such strong gravitational fields. Observing more black holes will allow us to test Einstein’s theory and maybe detect a crack in his hitherto impenetrable armour.</p>
<p>This list of future developments is just scratching the surface of discovery space that is now open to us. Gravitational waves will reveal many more secrets of the universe in the coming years. </p>
<p>So the future of gravitational wave astronomy is bright and Australian scientists are fortunate to be part of this brand new and exciting field of discovery.</p>
<p>Continuing to invest in technology, infrastructure and data analysis development will further allow us to unveil other secrets of the universe; be it through observations of neutron star collisions, mountains on neutron stars, or even of the first moments of the universe itself.</p><img src="https://counter.theconversation.com/content/61080/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul Lasky does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
The observation of gravitational waves from a second black hole merger implies there are many more black holes in the universe than scientists had previously anticipated.
Paul Lasky, Lecturer, Monash University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/54839
2016-03-01T04:28:34Z
2016-03-01T04:28:34Z
Why it’s crucial that young scientists are taught the value of being wrong
<figure><img src="https://images.theconversation.com/files/113252/original/image-20160229-4066-s7g3sr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Children are natural scientists. They learn from their mistakes, then try something new.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Albert Einstein is the most famous scientist of all time. From Calgary to Cape Town the image of the wild-haired, contemplative lone genius holed up in a messy office, changing the universe, has evolved into the archetype of how society sees scientists. More than that, it has shaped the social perception of the whole scientific endeavour. </p>
<p>True science, we are led to believe from a very young age, is never wrong. True scientists – the <a href="http://www.history.com/topics/galileo-galilei">Galileos</a>, <a href="http://www.biography.com/people/isaac-newton-9422656">Newtons</a> and <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1903/marie-curie-bio.html">Curies</a> – stare into the abyss and return with deep truths about the universe we inhabit. Anything less and, well, you might as well throw in the towel. And so scientists spend their careers desperately trying to be right in every classroom, seminar and paper. </p>
<p>But this is not how science works. It’s not even how science is <em>supposed</em> to work. </p>
<p>The <a href="http://www.livescience.com/20896-science-scientific-method.html">scientific method</a> is built on four cornerstones: observation, hypothesis, experiment and the revision of the hypothesis based on the results of the experiment. The last is just a fancy way of saying “admitting that you were wrong”. </p>
<p>And since it is this sequence by which hypotheses evolve into theories which grow into paradigms, science itself cannot progress without scientists admitting – to themselves even more than to society at large - to being wrong.</p>
<h2>Even Einstein erred</h2>
<p>By now, few people are unaware of the recent monumental detection of <a href="https://theconversation.com/gravitational-waves-will-the-global-south-provide-the-next-pulse-of-gravity-research-54583">gravitational waves</a> by the LIGO team. This was heralded as the final great test of Einstein’s General Relativity. </p>
<p>But many people probably don’t know that in 1936 Einstein himself, together with Nathan Rosen, <a href="http://dafix.uark.edu/%7Edanielk/Talks/PhysRev.pdf">submitted a paper</a> for publication claiming that such gravitational waves could not exist. The paper was rejected. Einstein was wrong! It wasn’t the first, nor the last time either. </p>
<p>More recently, in 2014, the <a href="http://bicepkeck.org/">BICEP</a> collaboration announced that it had detected evidence of gravitational waves from the <a href="http://www.scientificamerican.com/article/what-is-the-cosmic-microw/">cosmic microwave background</a>. After much fanfare in popular media and back and forth in the scientific community, it emerged that they, too, <a href="http://physicsworld.com/cws/article/news/2014/sep/22/bicep2-gravitational-wave-result-bites-the-dust-thanks-to-new-planck-data">were wrong</a>. </p>
<p>So, why is it so important to realise that scientists being wrong is not a bug but a feature of science? </p>
<h2>Guarding the future of science</h2>
<p>First of all, we live in an age where information has never been more <a href="http://google.com/">accessible</a>. Ironically, with this growth of access to information has come a commensurate distrust in the expertise of scientists and even in the very science that has brought humankind to this juncture. </p>
<p>One has only to think of the surge of the anti-vaccine movement, resistance to GMOs, anxiety around wi-fi and even the raging non-battle between evolution and intelligent design. </p>
<p>In each of these cases, a small but vocal body pursuing its own agenda latched onto uncertainties and doubts expressed by scientists. Instead of appreciating this as the natural progression of the scientific process, these groups painted it as a dramatic failing of science and of scientists. </p>
<p>In some cases, as in former South African president Thabo Mbeki’s HIV/AIDS denialism, these views can have <a href="http://www.theguardian.com/world/2008/nov/26/aids-south-africa">life or death</a> consequences. </p>
<p>A second, perhaps more important reason, is for the very future of science itself. Even scientists sometimes don’t take the importance of being wrong seriously enough. This is due in no small part to the <a href="https://www.sciencedaily.com/terms/confirmation_bias.htm">confirmation bias</a> that seems built into our humanity. We are more likely to seek out and place value in information that confirms our own existing beliefs.</p>
<p>These views and the culture in which they form are then passed on to the next generation – our students pursuing science degrees at university.</p>
<h2>The way forward</h2>
<p>The current generation of students go through their degrees petrified of being wrong or of looking “stupid” among their peers and lecturers. This is particularly true in patriarchal environments that pervade Africa, where indeed many young people are taught not to question anything they’re told by elders.</p>
<p>And so no questions get asked. No guesses get made and no risks get taken as students grow more and more uncomfortable with being uncomfortable in lectures. For a continent that’s striving to produce the <a href="http://nef.org/">next Einstein</a>, this is a cycle that desperately needs breaking.</p>
<p>Fortunately breaking the cycle is not as difficult as it might seem. As much as we’d like to think otherwise, being wrong is something we as humans are inherently very good at. It is something that is manifest in how young children learn about the world, through play.</p>
<p>Natural scientists learn by trial and error, without fear of getting the answer wrong. Perhaps we as adults, students and teachers alike ought to take some lessons from them, cast aside our egos and embrace losing to nature. </p>
<p>But what do we know – we’re probably wrong anyway.</p><img src="https://counter.theconversation.com/content/54839/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jeff Murugan receives funding from the National Research Foundation of South Africa. </span></em></p><p class="fine-print"><em><span>Amanda Weltman receives funding from the National Research Foundation of South Africa and the Department of Science and Technology of South Africa. </span></em></p>
Scientists being wrong is not a bug or a glitch – it’s a feature of science and mistakes can actually lead to new, deeper discoveries.
Jeff Murugan, Associate Professor of Mathematical Physics, University of Cape Town
Amanda Weltman, South African Research Chair in Physical Cosmology, Department of Mathematics and Applied Mathematics, University of Cape Town
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/54717
2016-02-19T11:08:56Z
2016-02-19T11:08:56Z
Extreme numbers: the unimaginably large and small pop up in recent experiments
<figure><img src="https://images.theconversation.com/files/111848/original/image-20160217-19245-q5aano.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's a lot of grains of sand, but numbers can get a whole lot bigger....</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/hisgett/2289454268">Tony Hisgett</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The physics world erupted in celebration this month with the confirmed <a href="http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html?_r=0">discovery</a> of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (<a href="http://www.ligo.org/">LIGO</a>) group. Predicted by Einstein a century ago, the discovery verifies his description of the universe in which space and time can warp and bend.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111566/original/image-20160215-22560-d43qif.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111566/original/image-20160215-22560-d43qif.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111566/original/image-20160215-22560-d43qif.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111566/original/image-20160215-22560-d43qif.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111566/original/image-20160215-22560-d43qif.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111566/original/image-20160215-22560-d43qif.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111566/original/image-20160215-22560-d43qif.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Orbiting black holes generate gravitational waves.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>And what is the evidence gathered by LIGO? A billion years ago, a pair of black holes of masses about 30 times that of the sun collided, releasing about three solar masses’ worth of energy in the form of gravitational waves. Those waves traveled through space and reached the LIGO antennas, one in Louisiana and one in Washington, seven milliseconds apart, vibrating the mirrors at the end of each antenna’s 2.5-mile-long vacuum tube by a mere four thousandths the diameter of a proton.</p>
<p>I’m no physicist, but the LIGO numbers intrigue me. In fact, I’ve noticed quite a few huge (and tiny) numbers in recently announced scientific advances, which got me to thinking about how real physical situations force us to deal with numbers so extreme they’re inconceivable.</p>
<p>Let’s unpack these numbers. The gravitational waves travel at the speed of light, so the black holes that generated them were roughly one billion light-years away from Earth. That’s more than 6 billion trillion miles, or 6 x 10²¹ miles. The energy that created the waves is roughly equivalent to the light output of a billion trillion suns. And the end result was nudging a pair of mirrors by 4 x 10⁻¹⁸ meters, an unfathomably small distance.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/0fKBhvDjuy0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption"><em>Powers of Ten,</em> by Charles and Ray Eames.</span></figcaption>
</figure>
<p>A great visualization of these scales can be seen in the classic film <em>Powers of Ten</em>, created by Charles and Ray Eames in 1977. It doesn’t go out as far as the black holes that created the gravitational waves, nor does it go as small as the movement of the LIGO mirrors, but it does give a great sense of the scales involved in the recent announcement.</p>
<h2>Even larger numbers</h2>
<p>Here’s a question: say you have 128 tennis balls. How many different ways can you arrange them so that each ball touches at least one other? You can stack them, lay them out in various grids, stack the layers and so on. There are probably a lot of configurations, right?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/111567/original/image-20160215-22560-fex3rr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/111567/original/image-20160215-22560-fex3rr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111567/original/image-20160215-22560-fex3rr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111567/original/image-20160215-22560-fex3rr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111567/original/image-20160215-22560-fex3rr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111567/original/image-20160215-22560-fex3rr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111567/original/image-20160215-22560-fex3rr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111567/original/image-20160215-22560-fex3rr.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">How many ways can tennis balls be arranged?</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/atomictaco/5390499643">Atomic Taco</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>This question was <a href="http://www.cam.ac.uk/research/news/how-many-ways-can-you-arrange-128-tennis-balls-researchers-solve-an-apparently-impossible-problem">answered recently</a> by a team of researchers at Cambridge University. The number of possible arrangements is on the order of 10²⁵⁰; that’s a 1 with 250 zeroes after it. To give a sense of how large this number is, note that there are only about 10⁸⁰ atoms in the universe. In fact, if we packed the known universe with protons, there would be only about 10¹²⁶ of them. So if we could somehow encode each configuration of the tennis balls on an atom (or even a subatomic particle), we would be able to get through only about the cube root of the total number of possibilities. </p>
<p>Since it’s impossible to actually count all the arrangements of the balls, the team used an indirect approach. They took a sample of all the possible configurations and computed the probability of each of them occurring. Extrapolating from there, the team was able to deduce the number of ways the entire system could be arranged, and how one ordering was related to the next. The latter is the so-called <a href="https://en.wikipedia.org/wiki/Configuration_entropy">configurational entropy</a> of the system, a measure of how disordered the particles in a system are.</p>
<p>This may seem like an odd calculation to make, but it is an important question in granular physics. This is the study of the behavior of materials that are granular in nature, such as sand or snow. If we wish to understand how sand dunes form and evolve over time, or how avalanches happen, we must first be able to enumerate the possible initial configurations of the particles. Clearly, 128 particles is nowhere near a large enough number for us to begin to understand a sand dune, but it’s a start. And the methods employed for this study may yield insights that will help attack bigger systems.</p>
<h2>Still bigger numbers</h2>
<p>A number such as 10²⁵⁰ is enormous, but relative to numbers “close” to infinity it is effectively zero. At scales like this, I find it comforting to turn to literature and philosophy. In “<a href="http://eduscapes.com/history/contemporary/babel.pdf">The Library of Babel</a>,” the fascinating short story by Jorge Luis Borges, we learn about a certain library in which each book has 410 pages, and each page has 40 lines of 80 characters. The alphabet in use has 22 letters and three punctuation marks, making a total of 25 orthographic characters. We are told that every possible book is somewhere in this imagined library. So, how many books are there? First note that there are 410 x 40 x 80 = 1,312,000 characters in each book and since we have 25 choices for each character, there are 25¹³¹²⁰⁰⁰ possible books. As a power of 10, that’s roughly 10¹⁸³⁴⁰⁹⁷.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/111995/original/image-20160218-1274-b5a2mf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/111995/original/image-20160218-1274-b5a2mf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111995/original/image-20160218-1274-b5a2mf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111995/original/image-20160218-1274-b5a2mf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111995/original/image-20160218-1274-b5a2mf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111995/original/image-20160218-1274-b5a2mf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111995/original/image-20160218-1274-b5a2mf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111995/original/image-20160218-1274-b5a2mf.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">A brick and mortar library, however grand, holds a beyond-minuscule amount of books compared to the imagined Library of Babel.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:George-peabody-library.jpg">Matthew Petroff</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>If we can’t wrap our heads around 10²⁵⁰, how are we to manage a number like this? Borges’ fictional library tells us how. While we can’t possibly enumerate a catalog of all the books, we can imagine any book we like. There is a completely blank book. There is a book with a single comma in the middle of page 204 and nothing else. There are actually 1,312,000 books with a single comma and nothing else (just in each of the possible locations). There is a book with only the letter y in every spot. This article you’re reading right now appears exactly as it is written (by spelling out the numbers and ignoring extraneous punctuation) in an enormous number of books in the library (10 to a very large power, certainly more than 1.7 million). It appears in every language on the planet (suitably translated into the alphabet). </p>
<p>If you want to play around with this idea, there is an <a href="https://libraryofbabel.info/">online Library of Babel</a> that catalogs every possible page of 3200 characters. This amounts to only about 10⁴⁶⁷⁷ books, a tiny fraction of the total library, but it’s great fun to search for strings of characters. Jonathan Basile, the site’s creator, has devised a scheme for cataloging the books based on Borges’ description of the library as a collection of hexagonal cells with a certain number of books on each shelf (only four of each cell’s six walls contain shelves). For example, the phrase “when in the course of human events” occurs by itself at the top of page 186 of volume 21 on shelf 1 of wall 3 of a hexagon labeled with a 3254-digit identifier in base 36. Whew. </p>
<p>And yet, despite the enormity of the Library of Babel, the number of books is less than the <a href="http://www.mersenne.org/primes/?press=M74207281">largest known prime number</a>, discovered in January 2016. The Mersenne number M74207281 = 2⁷⁴²⁰⁷²⁸¹ - 1 has more than 22 million digits, way more than the puny number of books in the library (only about 1.8 million digits). And there are surely larger primes out there (Euclid <a href="https://en.wikipedia.org/wiki/Euclid's_theorem">told us so</a>), with billions, trillions, or 10²⁵⁰ digits.</p>
<h2>Should we care?</h2>
<p>So, are these unimaginable numbers actually good for anything? In a practical sense, no. They are simply too large to be useful in everyday scientific computation (we need big primes for encryption algorithms, but not <em>that</em> big). And once you’ve counted every subatomic particle in the universe, there’s probably not much need for a bigger number. They do provide fertile ground for thought experiments, though, and illustrate the human capacity to ponder the unreasonably large (and small, too).</p><img src="https://counter.theconversation.com/content/54717/count.gif" alt="The Conversation" width="1" height="1" />
Scientific advances – including the recent discovery of gravitational waves – force us to deal with numbers so extreme they’re virtually inconceivable.
Kevin Knudson, Professor of Mathematics, University of Florida
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/54672
2016-02-16T15:07:21Z
2016-02-16T15:07:21Z
How did the odd black holes detected by LIGO form – and can we spot them in the sky?
<figure><img src="https://images.theconversation.com/files/111569/original/image-20160215-22566-1rab6wp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A needle in a haystack? Pan Starrs telescope is scanning billions of galaxies to find the black holes emitting gravitational waves.</span> <span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Great scientific discoveries often raise more questions than they answer. Just days after the announcement that gravitational waves from two merging black holes <a href="https://theconversation.com/gravitational-waves-found-the-inside-story-54589">have been detected</a>, astrophysicists are already pondering what this means for our understanding of stars. New studies are already being released and we can expect a flood of creative ideas in the near future. </p>
<p>One of the most surprising things about the discovery is the huge size of the black holes involved which is challenging our understanding of how they form. So how can we find out more? One way is by pinpointing the black holes on the sky so we can try to study them using regular telescopes. </p>
<h2>Massive mystery</h2>
<p>LIGO, the observatory that detected the gravitational waves, is a so-called <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">laser interferometer</a>. It estimated that the two merging black holes would have masses of about 36 and 29 times that of the sun respectively (described as 36 and 29 “<a href="http://astronomy.swin.edu.au/cosmos/s/solar+mass">solar masses</a>”), calculated from the frequency of the gravitational waves. But what’s so unusual about these masses?</p>
<p><a href="https://theconversation.com/explainer-black-holes-7431">Black holes</a> form after huge <a href="https://theconversation.com/short-sharp-shocks-let-slip-the-stories-of-supernovae-42118">supernovae explosions</a>, which can only be produced by massive stars. The masses of the black holes in our own galaxy can be measured by looking at the speed of stars orbiting a black hole. The most massive black hole in a binary system (a black hole and a companion star orbiting a common centre) in our galaxy is about 10-20 solar masses. </p>
<p>This is well explained by our knowledge of stars. The biggest stars are born at about 100 solar masses and end up at around only ten solar masses at their endpoints due to stellar winds blowing out material into space. This means they shouldn’t be able to produce the kind of huge black holes that LIGO detected. But there are still big uncertainties about the rate at which this occurs and the influence of a star’s spin, the existence of a second star orbiting a common centre (binary stars), and its chemical composition. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/111573/original/image-20160215-22563-1eaox8x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/111573/original/image-20160215-22563-1eaox8x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111573/original/image-20160215-22563-1eaox8x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111573/original/image-20160215-22563-1eaox8x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111573/original/image-20160215-22563-1eaox8x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111573/original/image-20160215-22563-1eaox8x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111573/original/image-20160215-22563-1eaox8x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111573/original/image-20160215-22563-1eaox8x.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">Multi-wavelength compilation image of Kepler’s supernova remnant, SN 1604.</span>
<span class="attribution"><span class="source">NASA/wikimedia</span></span>
</figcaption>
</figure>
<p>So how could the black holes detected by LIGO be so massive? <a href="http://arxiv.org/abs/1602.03846">Research has already come out</a> that suggests we can explain that by assuming they come from two collapsing massive stars. But the stars that formed them must have had a very different chemical composition to the stars in our own Milky Way, which has a high content of heavy chemical elements like oxygen, sodium, magnesium, silicon, sulphur, iron. </p>
<p>In fact, <a href="http://arxiv.org/abs/1602.03846">a paper from the LIGO team</a> and <a href="http://arxiv.org/abs/1602.03790">one from two experts on binary stars</a> proposed that they needed to be in small galaxies with very low metal content (we astronomers label all elements heavier than boron a “metal”). That’s because, according to atomic physics, low-metal stars lose less mass during their life. So they end up with higher mass than other stars at the end, and form larger black holes. </p>
<h2>Sky scanning</h2>
<p>The LIGO team could give a rough direction of where on the sky the merger took place, due to the difference in detection <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">time between its two experiments</a> in different parts of the US (0.07 seconds). However this can only be located to about 500 square degrees (an area of 2,000 full moons). Astronomers tried to pinpoint the source by pointing optical, infrared, X-ray and radio telescopes in this area.</p>
<p>However, it wasn’t easy. Black hole mergers are not predicted to produce significant <a href="https://theconversation.com/explainer-what-is-the-electromagnetic-spectrum-8046">electromagnetic radiation</a> such as visible light or X-rays. But there was <a href="http://arxiv.org/abs/1602.03920">an intriguing detection of gamma-rays</a> (which are high-energy electromagnetic waves) by the Fermi satellite that lasted just a second and appeared 0.4 seconds after the LIGO signal. However, it is not certain that the two are related, as Fermi can’t tell where these gamma rays came from in the sky. The next step is to look for more high-energy emissions coincident in time with future gravitational wave signals to see whether there’s a link. There <a href="http://arxiv.org/abs/1602.04735">are indeed theories</a> that suggest that two merging holes can produce a gamma-ray burst if they form and merge in a certain way, meaning it is important to keep looking. </p>
<p>We <a href="http://www.qub.ac.uk/home/ceao/News/#d.en.565644">recently scanned the area</a> with the <a href="http://www.ifa.hawaii.edu/info/press-releases/LIGO-panstarrs/">Pan-STARRS telescope</a> and found 56 sources of optical light emissions, but we weren’t able to link any of them to the LIGO event. This is not too surprising, it’s tough to cover such a large area – including billions of galaxies – fast, deep and with broad wavelength coverage. There are some clever ideas to pick the biggest galaxies using catalogues and focus on observing those. However if these massive black holes have to come from metal-depleted stars, their host galaxies will be small because of where low-metal stars are found. These galaxies are much more numerous than large ones, and there are too many of them to use this method. Also, many of them are too faint to have been catalogued before. </p>
<p>It will definitely not be an easy observation to make, but what is certain is that we will be looking harder than ever. The world’s most powerful telescopes on the ground and in space are all joining the hunt. The journey is just starting and the LIGO discovery is truly inspiring.</p><img src="https://counter.theconversation.com/content/54672/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stephen Smartt receives funding from the ERC and the UK's STFC</span></em></p>
The hunt to find the source of the gravitational waves detected by LIGO on the sky is only just starting.
Stephen Smartt, Professor of Physics and Mathematics, Queen's University Belfast
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/54583
2016-02-12T09:26:15Z
2016-02-12T09:26:15Z
Gravitational waves: will the global south provide the next pulse of gravity research?
<figure><img src="https://images.theconversation.com/files/111285/original/image-20160212-29192-16yu5pg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This is a new era of physics and astronomy - and scientists all over the globe, including in Africa, have a role to play.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>A little over a century ago, on 25 November 1915, Albert Einstein published a paper entitled <a href="http://www.academia.edu/375613/Einsteins_Original_Paper_on_General_Relativity">“Die Feldgleichungen der Gravitation”</a>. Its contents would change the world forever. </p>
<p>Like any good scientific theory, Einstein’s General Relativity not only explained the shortcomings of its predecessor, in this case <a href="http://csep10.phys.utk.edu/astr161/lect/history/newtongrav.html">Newtonian gravity</a>, it also made predictions of new and unexpected phenomena. These included the bending of light by massive objects, the existence of black holes, the slowing down of time in strong gravitational fields and the very framework for the cosmology of the universe. All of these have withstood a century of <a href="http://physics.ucr.edu/%7Ewudka/Physics7/Notes_www/node97.html">intense scrutiny</a>. But for 100 years one particular prediction in Einstein’s theory of Gravity eluded the most ingenious testing.</p>
<p>That changed on 11 February 2016 with the <a href="https://www.ligo.caltech.edu/news/ligo20160211">news that gravitational waves</a> have been discovered. As so often happens in astronomy research, the real event took place over a billion years ago. The detection was in September 2015. But the full gravity of the situation is only being revealed now: this is a new era in astronomy and physics. </p>
<h2>The signal that started it all</h2>
<p>On 14 September 2015 the <a href="https://www.ligo.caltech.edu/">Advanced Laser Interferometer Gravitational-wave Observatory (LIGO)</a>, a newly upgraded, purpose-built gravitational wave detection experiment based in the USA, received a signal from a binary system of two massive black holes merging into a single larger one, 1.2 billion light years away. The final front’s here.</p>
<p>This event was so cataclysmic that the gravitational wave released in the final moments of the binary system’s mortal dance produced the first ever observed gravitational wave signal. It was so large that LIGO scientists report being able to visually <a href="https://twitter.com/PhysRevLett/status/697815592062074881">“see” the signal in the data</a>. </p>
<p>To put this in perspective, the level of accuracy needed to see this tiny ripple in spacetime required measuring a change in length of a 4km long channel the size of a fraction of the diameter of a proton! The level of certainty in this result is given, in physics terms, as a 5.1 sigma event. In simple terms, the likelihood that this is a coincidence is less than 1 in 3.5 million. </p>
<p>And it all goes back to Einstein.</p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/111282/original/image-20160212-4413-474ify.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/111282/original/image-20160212-4413-474ify.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=789&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111282/original/image-20160212-4413-474ify.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=789&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111282/original/image-20160212-4413-474ify.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=789&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111282/original/image-20160212-4413-474ify.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=991&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111282/original/image-20160212-4413-474ify.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=991&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111282/original/image-20160212-4413-474ify.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=991&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Albert Einstein.</span>
<span class="attribution"><span class="source">Reuters</span></span>
</figcaption>
</figure>
<h2>Evasive waves</h2>
<p>Although their existence had never been directly detected, gravitational waves - ripples in the very fabric of spacetime - are so-well studied that they are <a href="http://www.aei.mpg.de/%7Eschutz/download/lectures/AzoresCosmology/Schutz.AzoresLecture1.pdf">taught even to undergraduate students</a>.</p>
<p>So why are they so difficult to detect? One reason is that, unlike light, gravitational waves are incredibly weakly interacting and can pass through most matter, of arbitrary density, unhindered. A second one is that, unlike the electric force field which can be felt by individual charges in a detector, the gravitational field is <a href="https://en.wikipedia.org/wiki/Tidal_force">tidal in nature</a> and requires extensive apparatus to detect it. </p>
<p>Taken together, these would merely imply that any detection of gravitational waves would take some of the largest, most sensitive experimental apparatus ever built. Difficult, but surely not that difficult. After all we’ve built the <a href="http://home.cern/topics/large-hadron-collider">Large Hadron Collider</a> and discovered <a href="http://science.howstuffworks.com/higgs-boson.htm">the Higgs</a>. No, there is one more crucial element to this detection: luck. </p>
<p>Producing a gravitational wave large enough for us to detect out here in the galactic suburbs takes some of the most cataclysmic events in the universe, events matched in their violence only by how rare they are. Until now.</p>
<h2>Could Africa be next?</h2>
<p>Today, thanks to the remarkable work of more than 1000 scientists involved in LIGO, there is certainty: Einstein was right, again. </p>
<p>His theory about gravitational waves sparked a huge debate when it was first published, engaging some of the world’s most famous scientists. The <a href="https://www.youtube.com/watch?v=TWqhUANNFXw">beautiful chirp</a> heard across the world on 11 February 2016 was the final word in this particular century-long conversation. However, the next phase of the conversation is far from over. </p>
<p>Physicists and astronomers have learnt so much, yet our work is far from done. The next frontier is here. Where will be the next big announcement be made in this new era? Who will write the next chapter in this intergenerational dialogue? Today is a day for boldness. So allow us, as African scientists, to be bold. With the <a href="https://www.skatelescope.org/">Square Kilometre Array</a> project to be constructed across Africa and Australia, the global South and indeed Africa itself is poised to provide the next pulse of gravity research. Our time has come.</p><img src="https://counter.theconversation.com/content/54583/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Amanda Weltman receives funding from the National Research Foundation of South Africa and the Department of Science and Technology of South Africa. </span></em></p><p class="fine-print"><em><span>Jeff Murugan receives funding from the National Research Foundation of South Africa. </span></em></p>
The discovery of gravitational waves has ushered in a new era in astronomy and physics. Where will the next big discovery be made? There’s no reason for it not to be Africa.
Amanda Weltman, South African Research Chair in Physical Cosmology, Department of Mathematics and Applied Mathematics, University of Cape Town
Jeff Murugan, Associate Professor of Mathematical Physics, University of Cape Town
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/54525
2016-02-12T06:00:43Z
2016-02-12T06:00:43Z
Australia’s part in the global effort to discover gravitational waves
<p>The historic <a href="https://theconversation.com/au/topics/gravitational-wave-discovery">discovery of gravitational waves</a> <a href="https://www.ligo.caltech.edu/news/ligo20160211">announced this week</a> involved the work of more than a thousand scientists working tirelessly in several different institutions, across many different countries and timezones.</p>
<p>Why is an entire village, albeit a diverse and disparate one, required to verify experimentally the last of Einstein’s major predictions in his theory of general relativity? And how does such a village function and coordinate in such a way that maximises scientific output?</p>
<h2>A tour of the village</h2>
<p><a href="http://www.ligo.org/">LIGO Scientific Collaboration</a> consists of <a href="https://theconversation.com/gravitational-waves-discovered-how-did-the-experiment-at-ligo-actually-work-54510">two individual experiments</a>, located at two sites in the United States, separated by 3,000 kilometres. At each site, a single, very high-power laser beam is split in two, and travels down two perpendicular four kilometre-long vacuum tunnels.</p>
<p>At the ends of these tunnels the laser hits large, 40-kilogram mirrors suspended by an intricate series of pendula to reduce shaking from external forces.</p>
<p>The laser light returns along the same tunnel, and recombines. Gravitational waves cause the actual length of each arm to change. The way the laser light recombines is used to determine this change.</p>
<p>In order to make a detection, the LIGO instruments needed to measure a change in arm length equal to 1,000th the diameter of a proton. Performing such a measurement is a remarkable technological feat that involves development across multiple scientific streams.</p>
<p>These fields include, but are not limited to; quantum physics and quantum metrology; high-powered optics; mechanical systems including thermal and vibrational control systems; general relativity and gravitation; theoretical astrophysics and traditional astronomy; large-scale computing … the list goes on. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/111279/original/image-20160212-29172-xz618n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/111279/original/image-20160212-29172-xz618n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111279/original/image-20160212-29172-xz618n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111279/original/image-20160212-29172-xz618n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111279/original/image-20160212-29172-xz618n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111279/original/image-20160212-29172-xz618n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111279/original/image-20160212-29172-xz618n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111279/original/image-20160212-29172-xz618n.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">LIGO Laboratory operates two detector sites, one near Hanford in eastern Washington, and another near Livingston, Louisiana. This photo shows the Hanford detector site.</span>
<span class="attribution"><a class="source" href="https://www.ligo.caltech.edu/image/ligo20150731f">LIGO/Caltech</a></span>
</figcaption>
</figure>
<p>The multidisciplinary nature of this experiment is reflected in the structure of the LIGO Scientific Collaboration (LSC), which looks more like a corporate entity than a traditional scientific collaboration.</p>
<p>Among other things, there are many, many science working groups which fall within the scope of three main themes: instrument science, detector characterisation and data analysis.</p>
<p>Alongside the science working groups sit groups such as Education and Public Outreach, Diversity, and the Presentation and Publications Committee. </p>
<p>Each working group is a dynamic, scientific collaboration all unto themselves. Each has a chairperson, or multiple co-chairs, who report to the theme leaders who, in turn, report to the LSC spokesperson, executive committee and council.</p>
<h2>Who works in the village?</h2>
<p>So exactly how many scientists does it take to detect a gravitational wave? This particular effort took 1,006 scientists working tirelessly in 16 countries in 83 different institutions, located in 14 different timezones!</p>
<p>Research for the discovery was done all over North America, Brazil, throughout Europe, Russia, India, China and South-East Asia and Australia. </p>
<p>We, along with about 50 colleagues, work on this experiment in Australia. A majority of the leadership group work in institutes in the US, at places such as CalTech and MIT.</p>
<p>The result of this unfortunate circumstance is that full, collaboration-wide teleconferences typically take place between 2am and 4am in Australian time. Over the past two months, building to the announcement, this has affected our lives many times!</p>
<p>In general, science working groups hold weekly teleconferences. Many of us are part of working groups that only exist on two continents, making it possible to schedule meetings that also allow for a relatively normal existence. </p>
<p>Many of us also work in groups that have numerous members on three or more continents; very early, or very late teleconferences are not uncommon, but remind us of the scale of the collaboration and the international effect of our work.</p>
<h2>What do they do?</h2>
<p>As mentioned before, this is a precision measurement! Every aspect of the experiment is incredibly finely-tuned. For example, multiple groups and individuals around Australia work on the technology and design of the mirrors.</p>
<p>Monash University researcher Yuri Levin, while a PhD student of Kip Thorne’s at CalTech, developed the theoretical framework for computing thermal noise (which is now widely used within the collaboration). From this work it became clear that LIGO mirrors require exceptionally high-quality reflective coatings.</p>
<p>The coating noise Levin anticipated is now considered to be among the most serious sources of noise in the LIGO experiment.</p>
<p>Scientists at Adelaide University developed, installed and commissioned wavefront sensors for the LIGO mirrors that measure the mirrors’ change in shape due to the temperature of the high-powered laser, and corrects these distortions.</p>
<p>Researchers at CSIRO developed mirror coatings and polishing techniques for the initial phase of the LIGO experiment that lasted from 2002 to 2010. A team at the Australian National University developed tip-tilt mirror suspension systems that can be used to steer the laser light with remarkable accuracy.</p>
<p>A group at the University of Western Australia have built a mini-LIGO experiment that is used, among other things, to study an instability the high-powered laser can induce on the mirrors, causing them to wobble uncontrollably.</p>
<p>Each element and each component of the incredibly complex LIGO system undergoes incredible levels of development and scrutiny. </p>
<p>This is perhaps best exemplified in the data analysis sphere. In Australia, we have strong groups at Monash University, the universities of Melbourne and Western Australia, the Australian National University and Charles Sturt University.</p>
<p>We all work on developing and running computer software that can pick a tiny signal out of noisy data streams. Somewhat infamously, LIGO puts itself through a process called blind injections.</p>
<p>Blind injections are performed by a very small group of people. The team inject a fake signal into the data stream by artificially shaking the mirrors of the detector in such a way that makes it looks like a gravitational wave has passed through.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/UkrM9pRy43M?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>The unsuspecting data analysts play their usual games of analysing this data and, lo and behold, inevitably find the signal.</p>
<h2>An early result?</h2>
<p>The most famous of these blind injections occurred in September 2010. Very soon after the signal was automatically injected into the detectors, it was picked up with the initial data analysis algorithms.</p>
<p>The purported signal looked like it to came from the constellation Canis Major, and the event was subsequently called the “Big Dog”. The collaboration then went through a six-month process of vetting, checking, and re-checking the analysis, and even wrote up a full paper to be submitted to the journal.</p>
<p>An independent Detection Committee reviewed all of the results, and a collaboration-wide vote was held on whether to submit the paper for peer review – the result was an anonymous “yes”.</p>
<p>And then the envelope was opened: the signal was fake.</p>
<p>That exercise, while incredibly painful to many, shows just how seriously the LIGO Scientific Collaboration takes its science. That this latest detection was not a blind injection has been known by the entire collaboration for a long time – the experiment was only beginning to collect data, and the blind injection software had not yet been set up properly.</p>
<p>Less than one hour after the LIGO experiment wobbled from the gravitational wave on that fateful day on September 14, 2015, one of us (Lasky) and fellow Monash academic and LIGO researcher Eric Thrane, who sits on the fake injection committee, were sitting at our laptops at home when we both received an email titled “Very interesting event on ER8” (ER8 stands for Engineering Run 8, which was the name of the pre-science phase of the experiment).</p>
<p>A quick Skype conversation quickly ensued:</p>
<blockquote>
<p>Thrane: Have you seen the email?</p>
<p>Lasky: Yes. Is it a false injection?</p>
<p>Thrane: No! </p>
<p>Lasky: Did we just detect a gravitational wave?</p>
<p>Thrane: I think we did.</p>
</blockquote>
<p>And the rest, as they say, is history.</p>
<p>This is truly the dawn of a new age of discovery. The gravitational-wave universe has many untold stories to tell, and scientists across Australia are striving to tell the tale along with the rest of the world.</p><img src="https://counter.theconversation.com/content/54525/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
The discovery of gravitational waves involved a team of more than 1,000 scientists from across the globe, including Australia. So how does such an international collaboration work?
Paul Lasky, Postdoctoral Fellow in Gravitational Wave Astrophysics, Monash University
Letizia Sammut, Postdoctoral research fellow in Gravitational Wave Astrophysics, Monash University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/54528
2016-02-12T00:09:33Z
2016-02-12T00:09:33Z
Timeline: the history of gravity
<figure><img src="https://images.theconversation.com/files/111240/original/image-20160211-29180-13i1prz.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p><em>Our understanding of gravity has gone through a few permutations, from Newton’s equations through to Einstein’s general relativity. With today’s discovery of gravitational waves, we look back on how our grasp of gravity has evolved over the centuries.</em></p>
<hr>
<h2>1687: Newtonian gravity</h2>
<p>Isaac Newton publishes <a href="http://cudl.lib.cam.ac.uk/view/PR-ADV-B-00039-00001/1">Philosophiae Naturalis Principia Mathematica</a>, giving a comprehensive account of gravity. This gave astronomers an accurate toolbox for predicting the motions of planets. But it was not without its problems, such as calculating the precise orbit of the planet Mercury.</p>
<p>All planets’ <a href="https://en.wikipedia.org/wiki/Precession">orbits precess</a> – with the closest point of their orbit moving slightly with each revolution – due to the gravitational tugs from other planets. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111236/original/image-20160211-29172-17upuhr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111236/original/image-20160211-29172-17upuhr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111236/original/image-20160211-29172-17upuhr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111236/original/image-20160211-29172-17upuhr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111236/original/image-20160211-29172-17upuhr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111236/original/image-20160211-29172-17upuhr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111236/original/image-20160211-29172-17upuhr.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The issue with Mercury’s orbit was that the amount of precession did not match what Newton’s theory predicted. It was only a small discrepancy, but big enough for astronomers to know it was there!</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111102/original/image-20160211-29198-to74rs.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111102/original/image-20160211-29198-to74rs.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=564&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111102/original/image-20160211-29198-to74rs.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=564&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111102/original/image-20160211-29198-to74rs.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=564&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111102/original/image-20160211-29198-to74rs.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=708&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111102/original/image-20160211-29198-to74rs.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=708&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111102/original/image-20160211-29198-to74rs.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=708&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">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>1859: Planet Vulcan</h2>
<p>To explain Mercury’s odd behaviour, <a href="http://www.britannica.com/biography/Urbain-Jean-Joseph-Le-Verrier">Urbain Le Verrier</a> proposed the existence of an unseen planet called [Vulcan](https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet), which orbited closer to the sun. He suggested that the gravity from Vulcan was influencing Mercury’s orbit. But repeated observations revealed no signs of Vulcan. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111103/original/image-20160211-29214-1q2fape.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111103/original/image-20160211-29214-1q2fape.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111103/original/image-20160211-29214-1q2fape.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111103/original/image-20160211-29214-1q2fape.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111103/original/image-20160211-29214-1q2fape.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111103/original/image-20160211-29214-1q2fape.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111103/original/image-20160211-29214-1q2fape.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>1905: Special relativity</h2>
<p>Albert Einstein shakes up physics with his <a href="https://theconversation.com/au/topics/special-relativity">special theory of relativity</a>. He then started incorporating gravity into his equations, which led to his next breakthrough.</p>
<h2>1907: Einstein predicts gravitational redshift</h2>
<p>What we now call gravitational redshift was first proposed by Einstein from his thoughts in the development of general relativity.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111104/original/image-20160211-29175-hjyke5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111104/original/image-20160211-29175-hjyke5.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=248&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111104/original/image-20160211-29175-hjyke5.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=248&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111104/original/image-20160211-29175-hjyke5.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=248&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111104/original/image-20160211-29175-hjyke5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=312&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111104/original/image-20160211-29175-hjyke5.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=312&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111104/original/image-20160211-29175-hjyke5.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=312&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">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Einstein predicted that the wavelength of light coming from atoms in a strong gravitational field will lengthen as it escapes the gravitational force. The longer wavelength shifts the photon to the red end of the electromagnetic spectrum.</p>
<h2>1915: General relativity</h2>
<p>Albert Einstein publishes <a href="https://theconversation.com/au/topics/general-relativity">general theory of relativity</a>. The first great success was its accurate prediction of Mercury’s orbit, including its previously inscrutable precession.</p>
<p>The theory also predicts the existence of black holes and <a href="https://theconversation.com/au/topics/gravitational-waves">gravitational waves</a>, although Einstein himself often struggled to understand them.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111105/original/image-20160211-29207-1udort5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111105/original/image-20160211-29207-1udort5.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111105/original/image-20160211-29207-1udort5.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111105/original/image-20160211-29207-1udort5.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111105/original/image-20160211-29207-1udort5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111105/original/image-20160211-29207-1udort5.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111105/original/image-20160211-29207-1udort5.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>1917: Einstein theorises stimulated emission</h2>
<p>In 1917, Einstein publishes a paper on the quantum theory of radiation indicating <a href="http://www.britannica.com/technology/stimulated-emission">stimulated emission</a> was possible.</p>
<p>Einstein proposed that an excited atom could return to a lower energy state by releasing energy in the form of photons in a process called spontaneous emission.</p>
<p>In stimulated emission, an incoming photon interacts with the excited atom, causing it to move to a lower energy state, releasing photons that are in phase and have the same frequency and direction of travel as the incoming photon. This process allowed for the development of the laser (light amplification by stimulated emission of radiation).</p>
<h2>1918: Prediction of frame dragging</h2>
<p><a href="https://en.wikipedia.org/wiki/Josef_Lense">Josef Lense</a> and <a href="https://www.aip.org/history-programs/niels-bohr-library/oral-histories/4912">Hans Thirring</a> theorise that the rotation of a massive object in space would “drag” spacetime around with it.</p>
<h2>1919: First observation of gravitational lensing</h2>
<p>Gravitational lensing is the bending of light around massive objects, such as a black hole, allowing us to view objects that lie behind it. During a total solar eclipse in May 1919, stars near the sun were observed slightly out of position. This indicated that light was bending due to the sun’s mass.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111106/original/image-20160211-29190-rgd6ni.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111106/original/image-20160211-29190-rgd6ni.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111106/original/image-20160211-29190-rgd6ni.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111106/original/image-20160211-29190-rgd6ni.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111106/original/image-20160211-29190-rgd6ni.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111106/original/image-20160211-29190-rgd6ni.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111106/original/image-20160211-29190-rgd6ni.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>1925: First measurement of gravitational redshift</h2>
<p><a href="http://www.britannica.com/biography/Walter-Adams">Walter Sydney Adams</a> examined light emitted from the surface of massive stars and detected a redshift, as Einstein predicted.</p>
<h2>1937: Prediction of a galactic gravitational lensing</h2>
<p>Swiss astronomer <a href="https://en.wikipedia.org/wiki/Fritz_Zwicky">Fritz Zwicky</a> proposed that an entire galaxy could act as a gravitational lens.</p>
<h2>1959: Gravitational redshift verified</h2>
<p>The theory was conclusively tested by <a href="https://en.wikipedia.org/wiki/Robert_Pound">Robert Pound</a> and <a href="https://en.wikipedia.org/wiki/Glen_Rebka">Glen Rebka</a> by measuring the relative redshift of two sources at the top and bottom of Harvard University’s Jefferson Laboratory tower. The experiment <a href="https://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment">accurately measured</a> the tiny change in energies as photons travelled between the top and the bottom.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111107/original/image-20160211-29202-6zzdjz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111107/original/image-20160211-29202-6zzdjz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111107/original/image-20160211-29202-6zzdjz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111107/original/image-20160211-29202-6zzdjz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111107/original/image-20160211-29202-6zzdjz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111107/original/image-20160211-29202-6zzdjz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111107/original/image-20160211-29202-6zzdjz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>1960: Laser invented using stimulated emission</h2>
<p><a href="http://www.laserinventor.com/bio.html">Theodore H. Maiman</a>, a physicist at Hughes Research Laboratories in California, builds the first laser.</p>
<h2>1960s: First evidence for black holes</h2>
<p>The 1960s was the beginning of the renaissance of general relativity, and saw the discovery of galaxies that were powered by the immense pull of <a href="https://theconversation.com/au/topics/black-holes">black holes</a> in their centres.</p>
<p>There is now evidence of massive black holes in the hearts of all large galaxies, as well as there being smaller black holes roaming between the stars.</p>
<h2>1966: First observation of gravitational time delays</h2>
<p>American astrophysicist Irwin Shapiro <a href="http://www.relativity.li/en/epstein2/read/i0_en/i3_en/">proposed</a> that if general relativity is valid, then radio waves will be slowed down by the sun’s gravity as they bounce around the solar system. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111108/original/image-20160211-29207-173wfss.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111108/original/image-20160211-29207-173wfss.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=404&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111108/original/image-20160211-29207-173wfss.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=404&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111108/original/image-20160211-29207-173wfss.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=404&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111108/original/image-20160211-29207-173wfss.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=507&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111108/original/image-20160211-29207-173wfss.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=507&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111108/original/image-20160211-29207-173wfss.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=507&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The effect was observed between 1966-7 by bouncing radar beams off the surface of Venus and measuring the time taken for the signals to return to Earth. The delay measured agreed with Einstein’s theory.</p>
<p>We now use time-delays on cosmological scales, looking at the time differences in flashes and flares between gravitationally lensed images to measure the expansion of the universe.</p>
<h2>1969: False detection of gravitational waves</h2>
<p>American physicist <a href="http://www.nytimes.com/2000/10/09/us/joseph-weber-dies-at-81-a-pioneer-in-laser-theory.html">Joseph Weber</a> (a bit of a rebel) claimed the first experimental detection of gravitational waves. His experimental results were never reproduced.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111109/original/image-20160211-29198-ynqrjq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111109/original/image-20160211-29198-ynqrjq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=668&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111109/original/image-20160211-29198-ynqrjq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=668&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111109/original/image-20160211-29198-ynqrjq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=668&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111109/original/image-20160211-29198-ynqrjq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=839&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111109/original/image-20160211-29198-ynqrjq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=839&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111109/original/image-20160211-29198-ynqrjq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=839&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">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>1974: Indirect evidence for gravitational waves</h2>
<p><a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/taylor-bio.html">Joseph Taylor</a> and <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/hulse-bio.html">Russell Hulse</a> discover a new type of pulsar: a binary pulsar. Measurements of the orbital decay of the pulsars showed they lost energy matching the amounts predicted by general relativity. They receive the 1993 <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/press.html">Nobel Prize for Physics</a> for this discovery.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111115/original/image-20160211-29202-1b945x2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111115/original/image-20160211-29202-1b945x2.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=639&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111115/original/image-20160211-29202-1b945x2.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=639&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111115/original/image-20160211-29202-1b945x2.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=639&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111115/original/image-20160211-29202-1b945x2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=802&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111115/original/image-20160211-29202-1b945x2.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=802&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111115/original/image-20160211-29202-1b945x2.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=802&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">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>1979: First observation of a galactic gravitational lens</h2>
<p>The first extragalactic gravitational lens was discovered, when observers <a href="https://en.wikipedia.org/wiki/Dennis_Walsh">Dennis Walsh</a>, <a href="http://www.ast.cam.ac.uk/%7Erfc/">Bob Carswell</a> and <a href="https://en.wikipedia.org/wiki/Ray_Weymann">Ray Weymann</a> saw two identical quasi-stellar objects, or “quasars”. It turned out to be one quasar that appears as two separate images.</p>
<p>Since the 1980s, gravitational lensing has become a powerful probe of the distribution of mass in the universe.</p>
<h2>1979: LIGO receives funding</h2>
<p>US National Science Foundation funds construction of the <a href="http://www.ligo.org/index.php">Laser Interferometer Gravitational-Wave Observatory</a> (LIGO).</p>
<h2>1987: Another false alarm for gravitational waves</h2>
<p>A false alarm on direct detection from Joseph Weber (again) with claimed signal from the supernova SN 1987A using his <a href="http://arxivblog.com/?p=1271">torsion bar experiments</a>, which consisted of large aluminium bars designed to vibrate when a large gravitational wave passed through it.</p>
<h2>1994: LIGO construction begins</h2>
<p>It took a long time, but the construction of LIGO finally began in Hanford, Washington, and Livingston, Louisiana.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111092/original/image-20160211-29180-1uw773l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111092/original/image-20160211-29180-1uw773l.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=436&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111092/original/image-20160211-29180-1uw773l.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=436&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111092/original/image-20160211-29180-1uw773l.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=436&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111092/original/image-20160211-29180-1uw773l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=548&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111092/original/image-20160211-29180-1uw773l.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=548&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111092/original/image-20160211-29180-1uw773l.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=548&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<h2>2002: LIGO starts first search</h2>
<p>In August 2002, LIGO starts searching for evidence of gravitational waves.</p>
<h2>2004: Frame dragging probe</h2>
<p>NASA launches <a href="https://einstein.stanford.edu/MISSION/mission1.html">Gravity Probe B</a> to measure the spacetime curvature near the Earth. The probe contained gyroscopes that rotated slightly over time due to the underlying spacetime. The effect is stronger around a rotating object which “drags” spacetime around with it. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111116/original/image-20160211-29192-xld1xm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111116/original/image-20160211-29192-xld1xm.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=483&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111116/original/image-20160211-29192-xld1xm.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=483&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111116/original/image-20160211-29192-xld1xm.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=483&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111116/original/image-20160211-29192-xld1xm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=607&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111116/original/image-20160211-29192-xld1xm.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=607&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111116/original/image-20160211-29192-xld1xm.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=607&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">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The gyroscopes in Gravity Probe B rotated by an amount consistent with Einstein’s theory of general relativity.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/111112/original/image-20160211-29185-3ttewq.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/111112/original/image-20160211-29185-3ttewq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1270&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111112/original/image-20160211-29185-3ttewq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1270&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111112/original/image-20160211-29185-3ttewq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1270&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111112/original/image-20160211-29185-3ttewq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1596&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111112/original/image-20160211-29185-3ttewq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1596&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111112/original/image-20160211-29185-3ttewq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1596&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">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>2005: LIGO hunt ends</h2>
<p>After five searches, the first phase of LIGO ends with no detection of gravitational waves. The sensors then undergo an interim refit to improve sensitivity, called Enhanced LIGO.</p>
<h2>2009: Enhanced LIGO</h2>
<p>An upgraded version called Enhanced LIGO starts new hunt for gravitational waves.</p>
<h2>2010: Enhanced LIGO hunt ends</h2>
<p>Enhanced LIGO fails to detect and gravitational waves. A major upgrade, called Advanced LIGO begins.</p>
<h2>2014: Advanced LIGO upgrade completed</h2>
<p>The new Advanced LIGO has finished installation and testing and is nearly ready to begin a new search.</p>
<h2>2015: False alarm #3 for gravitational waves</h2>
<p>The indirect signature of gravitational waves in the early universe was claimed by the <a href="https://theconversation.com/scientists-at-work-building-up-bicep2-at-the-south-pole-to-make-discovery-of-the-year-24610">BICEP2 experiment</a>, looking at the cosmic microwave background. But it looks like this was <a href="https://theconversation.com/bicep2-gravity-wave-finding-clouded-by-interstellar-dust-32048">dust in our own galaxy</a> spoofing the signal.</p>
<h2>2015: LIGO upgraded again</h2>
<p>Advanced LIGO starts a new hunt for gravitational waves with four times the sensitivity of the original LIGO. In September, it detects a signal that looks likely to be from the collision between two black holes.</p>
<h2>2016: Gravitational wave detection confirmed</h2>
<p>After rigorous checks, the Advanced LIGO team announce the <a href="https://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">detection</a> of gravitational waves.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111113/original/image-20160211-29214-szegpl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111113/original/image-20160211-29214-szegpl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111113/original/image-20160211-29214-szegpl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111113/original/image-20160211-29214-szegpl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111113/original/image-20160211-29214-szegpl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111113/original/image-20160211-29214-szegpl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111113/original/image-20160211-29214-szegpl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Wes Mountain/The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/54528/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Geraint Lewis receives funding from the Australian Research Council.</span></em></p>
It’s taken centuries for our understanding of gravity to evolve to where it is today, culminating in the discovery of gravitational waves, as predicted by Albert Einstein a century ago.
Geraint Lewis, Professor of Astrophysics, University of Sydney
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/53677
2016-02-11T16:05:13Z
2016-02-11T16:05:13Z
The logic of journal embargoes: why we have to wait for scientific news
<figure><img src="https://images.theconversation.com/files/111203/original/image-20160211-29190-1yx92jl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Extra, extra! The embargo's lifted, read all about it.</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic.mhtml?id=248829895&src=id">Newspapers image via www.shutterstock.com.</a></span></figcaption></figure><p>Rumors were flying through the blogosphere this winter: physicists at the Advanced Laser Interferometer Gravitational-Wave Observatory (<a href="https://www.ligo.caltech.edu/">LIGO</a>) may finally have directly detected <a href="http://www.nature.com/news/gravitational-waves-6-cosmic-questions-they-can-tackle-1.19337">gravitational waves</a>, ripples in the fabric of space-time predicted by Einstein 100 years ago in his general theory of relativity. Gravitational waves were predicted to be produced by cataclysmic events such as the collision of two black holes.</p>
<p>If true, it would be a very big deal: a rare chance for scientists to grab the attention of the public through news of cutting-edge research. So why were the scientists themselves keeping mum?</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"686574829542092800"}"></div></p>
<p>This wouldn’t be the first time scientists thought they had detected gravitational waves. In March 2014, a group claimed to have done so. In that case, scientists announced their discovery when they posted an article in <a href="http://arxiv.org">arXiv</a>, a preprint server where physicists and other scientists share research findings prior to acceptance by a peer-reviewed publications. Turns out that group was <a href="http://www.nature.com/news/gravitational-waves-discovery-now-officially-dead-1.16830">wrong</a> – they were actually looking at galactic dust. </p>
<p>The LIGO scientists were more careful. Fred Raab, head of the LIGO laboratory, <a href="http://www.geekwire.com/2016/after-gravitation-wave-rumors-its-getting-close-to-go-time-for-advanced-ligo-results/">explained</a>:</p>
<blockquote>
<p>As we have done for the past 15 years, we take data, analyze the data, write up the results for publication in scientific journals, and once the results are accepted for publication, we announce results broadly on the day of publication or shortly thereafter. </p>
</blockquote>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"686587441478766592"}"></div></p>
<p>And that’s what they did, timing their news conferences and media outreach to coincide with the <a href="http://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.116.061102">official publication</a> in the scientific journal Physical Review Letters about their discovery. Why did they delay their public announcement rather than spread the word as widely as possible as soon as possible?</p>
<h2>Science’s standard operating procedure</h2>
<p>Although it may sound unnecessarily cautious, the process Raab described is how most scientists prepare and vet discoveries prior to announcing them to the world – and, indeed, it’s the process most scientific journals insist upon. <em>Nature</em>, for example, <a href="http://www.nature.com/authors/policies/embargo.html">prohibits</a> authors from speaking with the press about a submitted paper until the week before publication, and then only under conditions set by the journal. </p>
<p>Scientific publishing serves both the scientist and the public. It’s a quid pro quo: the authors get to claim priority for the result – meaning they got there before any other scientists did – and in return the public (including competing scientists) gets access to the experimental design, the data and the reasoning that led to the result. Priority in the form of scientific publishing earns scientists their academic rewards, including more funding for their research, jobs, promotions and prizes; in return, they reveal their work at a level of detail that other scientists can build on and ideally replicate and confirm. </p>
<p>News coverage of a scientific discovery is another way for scientists to claim priority, but without the vetted scientific paper right there alongside it, there is no quid pro quo. The claim is without substance, and the public, while titillated, does not benefit – because no one can act on the claim until the scientific paper and underlying data are available.</p>
<p>Thus, most scientific journals insist on a “press embargo,” a time during which scientists and reporters who are given advanced copies of articles agree not to publish in the popular press until the scientific peer review and publishing process is complete. With the advent of <a href="http://www.infotoday.com/searcher/oct00/tomaiuolo&packer.htm">preprint servers</a>, however, this process itself is evolving. </p>
<p><a href="http://dx.doi.org/10.1056/NEJM197706022962204">First introduced</a> in 1977, journal embargoes reflect a scientific journal’s desire both to protect its own <a href="http://dx.doi.org/10.1056/NEJM198110013051408">newsworthiness</a> and to protect the public from misinformation. If a result is wrong (as was the case with the 2014 gravitational wave result), peer review is supposed to catch it. At the least, it means experts other than the researchers themselves examined the experimental design and the data and agreed that the conclusions were justified and the interpretations reasonable. </p>
<p>Often, results are more “nuanced” than the news article or press conference suggests. Yes, this new drug combination makes a (minor) difference, but it doesn’t cure cancer. Finally, the result could be correct, but not because of the data in that paper, and the premature press conference claims an unwarranted priority that can disrupt other research. In all these cases, having access to the research article and the underlying data is critical for the news to be meaningful.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/111035/original/image-20160210-12153-9yc2pi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/111035/original/image-20160210-12153-9yc2pi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111035/original/image-20160210-12153-9yc2pi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111035/original/image-20160210-12153-9yc2pi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111035/original/image-20160210-12153-9yc2pi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111035/original/image-20160210-12153-9yc2pi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111035/original/image-20160210-12153-9yc2pi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111035/original/image-20160210-12153-9yc2pi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Peer-reviewed and published.</span>
<span class="attribution"><span class="source">Maggie Villiger</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Purposes of a press embargo</h2>
<p>A press embargo has additional benefits for the reporter, the journal and the public.</p>
<p>Multiple journalists get an equal chance to publish a well-researched and balanced article. In exchange for respecting the journal’s press embargo, reporters find out what’s being published in advance of publication. This gives multiple journalists a chance to read the scientific article, find experts who can help them make sense of the article, and publish a carefully crafted story. From the scientist’s (and scientific journal’s) perspective, this maximizes the quality and quantity of the coverage by the press.</p>
<p>The public gains access to the scientific article very close to the time they read the news story. The popular press tends to bias a story toward what’s “newsworthy” about it – and that sometimes winds up exaggerating or otherwise inaccurately summarizing the scientific article. When that article relates to human health, for instance, it’s important that doctors have access to the original scientific paper before their patients start inquiring about new treatments they’d heard about in the news.</p>
<p>Other scientific experts gain access to the scientific article as soon as the findings become news. Scientists who jump the gun and allow their research to become news before publication in an academic journal are making unvetted claims that can turn out to be less important once the peer-reviewed article eventually appears.</p>
<p>A press embargo can protect a scientist’s claim for priority in the face of competition from other scientists and journals. Scientists generally accept journal publication dates as indicators of priority – but when a discovery makes news, the journal considering a competitor’s paper often both releases its authors from the embargo and races the paper to publication. And, if your competitor’s paper comes out first, you’ve lost the priority race.</p>
<p>The embargo system allows time for prepublication peer review. Most experiments designed to address research questions are complicated and indirect. Reviewers often require additional experiments or analyses prior to publication. Prepublication peer review can take a long time, and its value <a href="http://dx.doi.org/10.1242/dmm.001388">has been</a> <a href="https://www.theguardian.com/science/occams-corner/2015/sep/07/peer-review-preprints-speed-science-journals">questioned</a>, but it is currently the norm. If a news story came out on the paper while it was under review, the process of peer review could be jeopardized by pressure to “show the data” based on the news article. Many journals would decline publication under those conditions, leaving the authors and public in limbo.</p>
<p>I know of no case in which talking about a discovery in advance of scientific publication helps the public. Yes, “breaking news” is exciting. But journalists and other writers can tell riveting stories about science that convey the excitement of discovery without breaking journal embargoes. And the scientific community can continue to work on speeding its communication with the public while preserving the quid pro quo of scientific publication.</p><img src="https://counter.theconversation.com/content/53677/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Vivian Siegel 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>
Sometimes big research news bypasses the usual scientific publishing process. Here’s why that’s not good for scientists or the public.
Vivian Siegel, Visiting Instructor of Biological Engineering, Massachusetts Institute of Technology (MIT)
Licensed as Creative Commons – attribution, no derivatives.