tag:theconversation.com,2011:/us/topics/pulsar-6727/articlespulsar – The Conversation2022-10-28T09:26:10Ztag:theconversation.com,2011:article/1924472022-10-28T09:26:10Z2022-10-28T09:26:10ZZombie worlds: five spooky planets orbiting dead stars<figure><img src="https://images.theconversation.com/files/489593/original/file-20221013-17-wk1s48.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C3000%2C2398&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">PIA</span> <span class="attribution"><span class="source">NASA/JPL</span></span></figcaption></figure><p>All stars, including the Sun, have a finite lifetime. Stars shine by the process of nuclear fusion in which lighter atoms, such as hydrogen, fuse together to create heavier ones. This process releases vast quantities of energy which counteracts the ever-present inward pull of the star’s gravity. Ultimately, fusion helps stars to resist gravitational collapse. </p>
<p>This balance of forces is called “hydrostatic equilibrium”. However, there will come a time when the supply of fuel in the core of a star starts to run out and it eventually dies. Stars with more than about eight times the mass of the Sun will typically burn through their fuel in less than 100 million years. Once fusion ceases, the star collapses – generating a massive instantaneous final burst of nuclear fusion which causes the star to explode as a supernova. </p>
<p>Supernovas release enough energy to <a href="https://www.eso.org/public/images/ann11014a/">outshine the entire galaxy</a> in which they occur. What’s left afterwards are collapsed, dead stellar cores called neutron stars or, if the progenitor star was massive enough, a black hole. Any planets orbiting a star when it goes supernova would be <a href="https://getyarn.io/yarn-clip/0ea694af-2cb1-4a33-b0a5-b1b7f256ff4c/gif">obliterated</a>. Mysteriously though, <a href="https://academic.oup.com/mnras/article/512/2/2446/6542453?login=false">a handful</a> of “zombie planets” have been detected orbiting neutron stars. And they are some of the weirdest worlds in the cosmos.</p>
<p>Neutron stars are extremely dense, containing as much mass as the Sun squashed into a sphere only a few miles across. Some neutron stars emit beams of radio waves into space – and it is around these “pulsar” stars that planets have been found. As the pulsar spins, its radio beams sweep through space generating regular radio flashes. Pulsars were <a href="https://www.nature.com/articles/217709a0.pdf">discovered</a> in 1967 – you can listen to the sounds of the radio emission from some of them <a href="https://www.youtube.com/watch?v=gb0P6x_xDEU">here</a>.</p>
<p>The regularity of these radio pulses make pulsars ideal for hunting nearby planets. If a pulsar has a planet, they will both orbit a <a href="https://www.education.com/science-fair/article/barycenter-balancing-point/">shared gravitational centre</a>. This means the radio emission will be periodically stretched and compressed in a predictable fashion – allowing us to detect the planet.</p>
<h2>Phobetor, Draugr and Poltergeist</h2>
<p>Some 2,300 light years from Earth lies the pulsar <a href="https://exoplanets.nasa.gov/exoplanet-catalog/7134/psr-b125712-b/">PSR B1257+12</a>. It flashes 161 times per second and has been nicknamed “Lich” after an undead creature in western folklore. It is orbited by three rocky, terrestrial planets named Phobetor, Draugr and Poltergeist. </p>
<p>These planets hold a special place in the history of astronomy, as they were the first beyond our Solar System (exoplanets) to be <a href="https://www.sciencedirect.com/science/article/abs/pii/S1387647311000418">discovered</a> back in 1991. A few years ago, Nasa released this “zombie worlds” poster of them: </p>
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<img alt="Zombie world poster." src="https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/490353/original/file-20221018-14-d1hsi5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&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">Zombie world poster.</span>
<span class="attribution"><span class="source">Credit: NASA/JPL-Caltech</span></span>
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<p>Their discovery challenged ideas about planetary formation, which normally takes place as a new star forms. In contrast, these planets must have formed after the dying star’s supernova. It is not yet known with certainty how this happened. Material in a disk of debris orbiting the pulsar may have coalesced into planets after the supernova.</p>
<p>Draugr, named after an <a href="https://en.wikipedia.org/wiki/Draugr">undead creature in Norse mythology</a>, is the innermost of the three. It has about twice the mass of the Moon and is the least-massive planet currently known, orbiting Lich every 25 days. Its larger cousins, Poltergeist and Phobetor, orbit every 67 and 98 days respectively, and are each about four times the mass of Earth.</p>
<p>Pulsars have powerful magnetic fields which may allow electric currents to arc through space between the pulsar and an orbiting planet. So if any of these planets have atmospheres, they might constantly be bathed in the unearthly light of powerful aurora (similar to our northern lights).</p>
<p>If you were to stand on the surface of one of these zombie worlds, you would see, through the powerful hue of the aurora, the incandescent Lich in the sky projecting two powerful and tightly confined beams of light outwards in opposite directions into the blackness of space. Neutron stars can be extremely hot, carrying the residual heat left over from the supernova. Lich is nearly 30,000°C and the innermost of these worlds, Draugr, is likely to only be a few degrees below freezing at its surface.</p>
<h2>Diamond world</h2>
<p>Planet PSR J1719−1438b orbits a pulsar some 4,000 light years away, hurtling around its host in just over two hours. It is the densest planet yet discovered – so dense, in fact, that it is thought to be <a href="https://www.mpg.de/4406441/diamond_planet">composed largely of diamond</a>.</p>
<p>This “diamond world” is the <a href="https://arxiv.org/abs/1108.5201">remnant core</a> of a dead star called a <a href="https://imagine.gsfc.nasa.gov/science/objects/dwarfs2.html">white dwarf</a>. These are known to have a high carbon content (diamond is made of carbon) – but this particular white dwarf has lost 99.9% of its original mass, consumed by the powerful gravity of its nearby host pulsar.</p>
<p>This sphere of diamond is about half the size of Jupiter, and orbits PSR J1719-1438 at a distance of 600,000km (just 1.5 times further away than our Moon is from Earth). At such a close distance from its host pulsar, it is likely that this world has a very hot surface. </p>
<h2>Methuselah</h2>
<p>Orbiting the Milky Way (and many galaxies) are <a href="https://esahubble.org/wordbank/globular-cluster/#:%7E:text=Globular%20clusters%20are%20stable%2C%20tightly,and%20are%20tightly%20gravitationally%20bound.">globular star clusters</a> – spherical groups of up to a million stars each. These are some of the oldest stars in the universe.</p>
<p>The globular star cluster <a href="https://www.nasa.gov/feature/goddard/2017/messier-4">Messier M4</a> lies about 5,600 light years away and contains some 100,000 stars. Among these is a planet nicknamed Methuselah, after the son of Enoch in the Book of Genesis who supposedly lived for 969 years.</p>
<p>At the centre of the M4 star cluster is a pulsar and a white dwarf orbiting about their shared gravitational centre every 161 days. Given the short-lived nature of high-mass stars, the pulsar would have formed shortly after the formation of Messier 4 itself. </p>
<p>Methuselah also orbits this centre, but at a much more leisurely pace of once every 100 years or so, at a distance similar to that at which Uranus orbits our own Sun. It is a giant gas planet around 2.5 times the mass of Jupiter. Methuselah is believed to have formed as a normal planet around a Sun-like star within the first billion years of the formation of the universe. It was then captured into orbit around the host pulsar, which it has orbited ever since. </p>
<p>The high density of stars in globular clusters makes the chances of two stars having a close encounter quite high – and likewise the exchange of planets. Methuselah is the <a href="https://www.nasa.gov/centers/goddard/news/topstory/2003/0709hstssu.html">oldest known</a> planet in the cosmos, having formed an estimated 12.7 billion years ago along with all the stars in M4.</p>
<p>Pulsar planets are worlds of extremes, yet even they may not be the most bizarre. A small number of <a href="https://iopscience.iop.org/article/10.3847/1538-4357/ab4cf0">theoretical studies</a> have proposed the existence of planets orbiting black holes. So far, however, none have been found.</p><img src="https://counter.theconversation.com/content/192447/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gareth Dorrian does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A handful of zombie planets have been spotted – thought to have been born after the death of their host stars.Gareth Dorrian, Post Doctoral Research Fellow in Space Science, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1840502022-05-30T20:32:25Z2022-05-30T20:32:25ZThis newly discovered neutron star might light the way for a whole new class of stellar object<figure><img src="https://images.theconversation.com/files/465905/original/file-20220530-22-ktw8io.jpeg?ixlib=rb-1.1.0&rect=89%2C112%2C4902%2C3211&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>The discovery of a neutron star emitting unusual radio signals is rewriting our understanding of these unique star systems.</p>
<p>My colleagues and I (the <a href="https://www.meertrap.org/">MeerTRAP</a> team) made the discovery when observing the Vela-X 1 region of the Milky Way about 1,300 light years away from Earth, using the MeerKAT radio telescope in South Africa. We spotted a strange-looking flash or “pulse” that lasted about 300 milliseconds. </p>
<p>The flash had some characteristics of a radio-emitting neutron star. But this wasn’t like anything we’d seen before. </p>
<p>Intrigued, we scoured through older data from the region in hopes of finding similar pulses. Interestingly, we did identify more such pulses which had previously been missed by our real-time pulse detection system (since we typically only search for pulses lasting some 20-30 milliseconds).</p>
<p>A quick analysis of the times of arrival of the pulses showed them to be repeating about every 76 seconds – whereas <a href="https://www.skyatnightmagazine.com/space-science/neutron-star/">most neutron star</a> pulses cycle through within a few seconds, or even milliseconds.</p>
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<a href="https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram of a neutron star" src="https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=694&fit=crop&dpr=1 600w, https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=694&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=694&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=872&fit=crop&dpr=1 754w, https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=872&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/465906/original/file-20220530-16-7fh3ev.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=872&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Neutron stars are the collapsed cores of massive stars. Those that emit beams of electromagnetic radiation are classified as pulsars.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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<p>Our observation showed PSR J0941-4046 had some of the characteristics of a “pulsar” or even a “magnetar”. Pulsars are the extremely dense remnants of collapsed giant stars which usually emit radio waves from their poles. As they rotate, the radio pulses can be measured from Earth, a bit like how you’d see a lighthouse periodically flash in the distance.</p>
<p>However, the longest known rotation period for a pulsar before this was 23.5 seconds – which means we might have found a completely new class of radio-emitting object. Our findings are <a href="https://doi.org/10.1038/s41550-022-01688-x">published today</a> in Nature Astronomy.</p>
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Read more:
<a href="https://theconversation.com/a-brief-history-what-we-know-so-far-about-fast-radio-bursts-across-the-universe-154381">A brief history: what we know so far about fast radio bursts across the universe</a>
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<h2>An anomaly among neutron stars?</h2>
<p>Using all the data available to us from the MeerTRAP and <a href="http://www.thunderkat.uct.ac.za/">ThunderKAT</a> projects at MeerKAT, we managed to pinpoint the object’s position with excellent accuracy. After this we carried our more sensitive follow-up observations to study the source of the pulses. </p>
<p>The newly discovered object, named PSR J0941-4046, is a peculiar radio-emitting galactic neutron star which rotates extremely slowly compared to other pulsars. Pulsar pulse rates are incredibly consistent, and our follow-up observations allowed us to predict the arrival time of each pulse to a 100-millionth of a second.</p>
<p>Apart from the unexpected pulse rate, PSR J0941-4046 is also unique as it resides in the neutron star “graveyard”. This is a region of space where we don’t expect to detect any radio emissions at all, since it’s theorised the neutron stars here are at the end of their life cycle and therefore not active (or less active). PSR J0941-4046 challenges our understanding of how neutron stars are born and evolve.</p>
<p>It’s also fascinating as it appears to produce at least seven distinctly different pulse shapes, whereas most neutron stars don’t exhibit such variety. This diversity in pulse shape, and also pulse intensity, is likely related to the unknown physical emission mechanism of the object.</p>
<p>One particular type of pulse shows a strongly “quasi-periodic” structure, which suggests some kind of oscillation is driving the radio emission. These pulses may provide us with valuable information about the inner workings of PSR J0941-4046.</p>
<p>These quasi-periodic pulses bear some resemblance to enigmatic fast radio bursts, which are short radio bursts of unknown origin. However, it’s not yet clear whether PSR J0941-4046 emits the kind of energies observed in fast radio bursts. If we find it does, then it could be that PSR J0941-4046 is an “ultra-long period magnetar”.</p>
<p><a href="https://astronomy.swin.edu.au/cosmos/M/Magnetar">Magnetars</a> are neutron stars with very powerful magnetic fields, of which only a handful are known to emit in the radio part of the spectrum. While we’ve yet to actually identify an ultra-long period magnetar, they are theorised to be a possible source of fast radio bursts.</p>
<h2>Brief encounters</h2>
<p>It’s unclear how long PSR J0941-4046 has been active and emitting in the radio spectrum, since radio surveys typically don’t usually search for periods this long. </p>
<p>We don’t know how many of these sources might exist in the galaxy. Also, we can only detect radio emissions from PSR J0941-4046 for 0.5% of its rotation period – so it’s only visible to us for a fraction of a second. It’s pretty lucky we were able to spot it in the first place. </p>
<p>Detecting similar sources is challenging, which implies there may be a larger undetected population waiting to be discovered. Our finding also adds to the possibility of a new class of radio transient: the ultra-long period neutron star. Future searches for similar objects will be vital to our understanding of the neutron star population. </p>
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Read more:
<a href="https://theconversation.com/this-object-in-space-flashed-brilliantly-for-3-months-then-disappeared-astronomers-are-intrigued-175240">This object in space flashed brilliantly for 3 months, then disappeared. Astronomers are intrigued</a>
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<img src="https://counter.theconversation.com/content/184050/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Manisha Caleb acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 694745), an Australian Research Council Discovery Early Career Research Award (project number DE220100819) funded by the Australian Government and the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. </span></em></p>The object has a highly unusually long rotation period, and was found in an area we call the neutron star ‘graveyard’.Manisha Caleb, Lecturer, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1805082022-05-02T20:43:42Z2022-05-02T20:43:42ZWe’ve used a new technique to discover the brightest radio pulsar outside our own galaxy<figure><img src="https://images.theconversation.com/files/459633/original/file-20220426-24-1yteib.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1876%2C1235&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression of the PSR J0523-7125 in the Large Magellanic Cloud. </span> <span class="attribution"><span class="source">Carl Knox, ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)</span>, <span class="license">Author provided</span></span></figcaption></figure><p>When a star explodes and dies in a supernova, it takes on a new life of sorts. </p>
<p>Pulsars are the extremely rapidly rotating objects left over after massive stars have exhausted their fuel supply. They are extremely dense, with a mass similar to the Sun crammed into a region the size of Sydney. </p>
<p>Pulsars emit beams of radio waves from their poles. As those beams sweep across Earth, we can detect rapid pulses as often as hundreds of times per second. With this knowledge, scientists are always on the lookout for new pulsars within and outside our Milky Way galaxy.</p>
<p>In research <a href="https://iopscience.iop.org/article/10.3847/1538-4357/ac61dc">published today in the Astrophysical Journal</a>, we detail our findings on the most luminous radio pulsar ever discovered outside the Milky Way.</p>
<p>This pulsar, named PSR J0523-7125, is located in the Large Magellanic Cloud – one of our closest neighbouring galaxies – and is more than ten times brighter than all other radio pulsars outside the Milky Way. It may be even brighter than those within it.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/gjLk_72V9Bw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Source: Youtube/NASA.</span></figcaption>
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<h2>Why wasn’t PSR J0523-7125 discovered before?</h2>
<p>There are more than 3,300 radio pulsars known. Of these, 99% reside within our galaxy. Many were discovered with CSIRO’s famous Parkes radio telescope, <a href="https://blog.csiro.au/parkes-telescope-indigenous-name/">Murriyang</a>, in New South Wales. </p>
<p>About 30 radio pulsars have been found outside our galaxy, in the Magellanic Clouds. So far we don’t know of any in more distant galaxies. </p>
<p>Astronomers search for pulsars by looking for their distinctive repeating signals in radio telescope data. This is a computationally intensive task. It works most of the time, but this method can sometimes fail if the pulsar is unusual: such as very fast, very slow, or (in this case) if the pulse is very wide.</p>
<p>A very wide pulse reduces the signature “flickering” astronomers look for, and can make the pulsar harder to find. We now know PSR J0523-7125 has an extremely wide beam, and thus escaped detection. </p>
<p>The Large Magellanic Cloud has been explored by the Parkes telescope several times over the past 50 years, and yet this pulsar had never been spotted. So how were we able to find it?</p>
<h2>An unusual object emerges in ASKAP data</h2>
<p>Pulsar beams can be highly circularly polarised, which means the electric field of light waves rotate in a circular motion as the waves travel through space. </p>
<p>Such circularly polarised signals are very rare, and usually only emitted from objects with very strong magnetic fields, such as pulsars or dwarf stars.</p>
<p>We wanted to pinpoint unusual pulsars that are hard to identify with traditional methods, so we set out to find them by specifically detecting circularly polarised signals. </p>
<p>Our eyes can’t distinguish between polarised and unpolarised light. But the ASKAP radio telescope, owned and operated by Australia’s national science agency CSIRO, has the equivalent of <a href="https://blog.csiro.au/a-chance-encounter-with-a-pulsar/">polarised sunglasses that can recognise circularly polarised events</a>.</p>
<p>When looking at data from our ASKAP <a href="https://www.vast-survey.org/">Variables and Slow Transients</a> (VAST) survey, an undergraduate student noticed a circular polarised object near the centre of the Large Magellanic Cloud. Moreover, this object changed brightness over the course of several months: another very unusual property that made it unique.</p>
<p>This was unexpected and exciting, since there was no known pulsar or dwarf star at this position. We figured the object must be something new. We observed it with many different telescopes, at different wavelengths, to try and solve the mystery. </p>
<p>Apart from the Parkes (Murriyang) telescope, we used the space-based <a href="https://swift.gsfc.nasa.gov/">Neil Gehrels Swift Observatory</a> (to observe it at X-ray wavelengths) and the <a href="https://www.gemini.edu/">Gemini telescope</a> in Chile (to observe it at infrared wavelengths). Yet we detected nothing. </p>
<p>The object couldn’t be a star, as stars would be visible in optical and infrared light. It was unlikely to be a normal pulsar, as the pulses would have been detected by Parkes. Even the Gemini telescope didn’t provide an answer.</p>
<p>Ultimately we turned to the new, highly sensitive <a href="https://www.sarao.ac.za/science/meerkat/">MeerKAT radio telescope</a> in South Africa, owned and operated by the South African Radio Astronomy Observatory. Observations with MeerKAT revealed the source is indeed a new pulsar, PSR J0523-7125, spinning at a rate of about three rotations per second. </p>
<p>Below you can see the MeerKAT image of the pulsar with polarised “sunglasses” on (left) and off (right). If you move the slider, you’ll notice PSR J0523-7125 is the only bright object when the glasses are on.</p>
<iframe frameborder="0" class="juxtapose" width="100%" height="600" src="https://cdn.knightlab.com/libs/juxtapose/latest/embed/index.html?uid=241ff938-c4fa-11ec-b5bb-6595d9b17862"></iframe>
<p>Our analysis also confirmed its location within the Large Magellanic Cloud, about 160,000 light years away. We were surprised to find PSR J0523-7125 is more than ten times brighter than all other pulsars in that galaxy, and possibly the brightest pulsar ever found.</p>
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Read more:
<a href="https://theconversation.com/fifty-years-ago-jocelyn-bell-discovered-pulsars-and-changed-our-view-of-the-universe-88083">Fifty years ago Jocelyn Bell discovered pulsars and changed our view of the universe</a>
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<h2>What new telescopes can do</h2>
<p>The discovery of PSR J0523-7125 demonstrates our ability to find “missing” pulsars using this new technique. </p>
<p>By combining this method with ASKAP’s and MeerKAT’s capabilities, we should be able to discover other types of extreme pulsars – and maybe even other unknown objects that <a href="https://theconversation.com/we-found-a-mysterious-flashing-radio-signal-from-near-the-centre-of-the-galaxy-167802">are hard to explain</a>. </p>
<p>Extreme pulsars are one of the missing pieces in the vast picture of the pulsar population. We’ll need to find more of them before we can truly understand pulsars within the framework of modern physics.</p>
<p>This discovery is just the beginning. ASKAP has now finished its pilot surveys and is expected to launch into full operational capacity later this year. This will pave the way for even more discoveries, when the global <a href="https://www.skatelescope.org/">SKA</a> (square kilometre array) telescope network starts observing in the not too distant future. </p>
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<p><em>Akncowledgement: We acknowledge the Wajarri Yamatji as the traditional owners of the Murchison Radio-astronomy Observatory site where ASKAP is located, and the Wiradjuri people as the traditional owners of the Parkes Observatory.</em></p><img src="https://counter.theconversation.com/content/180508/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Yuanming Wang receives support from the China Scholarship Council, and as a Graduate Student with the University of Sydney and CSIRO Astronomy and Space Science. </span></em></p><p class="fine-print"><em><span>David Kaplan receives funding from the National Science Foundation.</span></em></p><p class="fine-print"><em><span>Tara Murphy receives funding from the Australian Research Council.</span></em></p>The pulsar PSR J0523-7125 is more than ten times brighter than any other radio pulsar outside the Milky Way.Yuanming Wang, PhD student, University of SydneyDavid Kaplan, Professor of Physics, University of Wisconsin-MilwaukeeTara Murphy, Professor, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/948152018-04-11T20:06:51Z2018-04-11T20:06:51ZCaptured! Radio telescope records a rare ‘glitch’ in a pulsar’s regular pulsing beat<figure><img src="https://images.theconversation.com/files/214213/original/file-20180411-560-1dkl4zt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Vela pulsar makes about 11 complete rotations every second, it also has a glitch.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/chandra/multimedia/vela2012.html">X-ray: NASA/CXC/Univ of Toronto/M.Durant et al; Optical: DSS/Davide De Martin</a></span></figcaption></figure><p>Pulsars are rapidly rotating neutron stars and sometimes they abruptly increase their rotation rate. This sudden change of spin rate is called a “glitch” and I was part of a team that recorded one happening in the Vela Pulsar, with the results <a href="http://nature.com/articles/doi:10.1038/s41586-018-0001-x">published today in Nature</a>.</p>
<p>Approximately 5-6% of pulsars are known to glitch. The Vela pulsar is perhaps the most famous – a very southern object that spins about 11.2 times per second and was discovered by scientists in Australia in 1968.</p>
<p>It is 1,000 light-years away, its supernova occurred about 11,000 years ago and roughly once every three years this pulsar suddenly speeds up in rotation.</p>
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Read more:
<a href="https://theconversation.com/fifty-years-ago-jocelyn-bell-discovered-pulsars-and-changed-our-view-of-the-universe-88083">Fifty years ago Jocelyn Bell discovered pulsars and changed our view of the universe</a>
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<p>These glitches are unpredictable, and one has never been observed with a radio telescope large enough to see individual pulses.</p>
<p>To understand what the glitch may be, first we need to understand what makes a pulsar.</p>
<h2>Collapsing stars</h2>
<p>At the end of a typical star’s life, one of three things can happen.</p>
<p>A small star, similar to the size of our Sun, will just quietly expire like a fire going out. </p>
<p>If the star is sufficiently large, a supernova will occur. After this massive explosion the remains will collapse. If the object is sufficiently large then its escape velocity will be greater than the speed of light, and a <a href="http://astronomy.swin.edu.au/cosmos/B/Black+Hole">black hole</a> will be formed.</p>
<p>But if we have a Goldilocks-sized star that is large enough to go <a href="http://astronomy.swin.edu.au/cosmos/S/Supernova">supernova</a>, but small enough not to be a black hole, we get a <a href="http://astronomy.swin.edu.au/cosmos/N/Neutron+Star">neutron star</a>.</p>
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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>
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<p>The gravity is so strong that the electrons orbiting the atom are forced into the nucleus. They combine with protons in the nucleus to form neutrons.</p>
<p>These objects are estimated to have a mass of about 1.4 times the mass of our Sun, and a diameter of 20km. The density is such that a cupful of this material would weigh as much as Mt Everest.</p>
<p>They also rotate quite quickly (and very gradually slow down over time) as well as having a massive magnetic field, three trillion times that of the Earth. Electromagnetic radiation emits from both ends of this huge rotating magnet. </p>
<p>Now if one of the poles of this rotating magnet happens to sweep past Earth, we see a brief “flash” in radio waves (and other frequencies too) once every rotation. This is called a <a href="http://astronomy.swin.edu.au/cosmos/P/Pulsar">pulsar</a>.</p>
<h2>The hunt for a ‘glitch’</h2>
<p>In 2014 I started a serious observing campaign with the University of Tasmania’s 26m radio telescope, at the <a href="http://www.utas.edu.au/maths-physics/facilities/mt-pleasant-observatory">Mount Pleasant Observatory</a>, with a goal to catch the Vela Pulsar’s glitch live in action.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214214/original/file-20180411-587-uzlsa9.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The 26m antenna at the Mount Pleasant Radio Observatory.</span>
<span class="attribution"><span class="source">University of Tasmania</span>, <span class="license">Author provided</span></span>
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<p>I collected data at the rate of 640MB for each 10 second file, for 19 hours a day, for most days over nearly four years. This resulted in over 3PB of data (1 petabyte is a million gigabytes) that was collected, processed and analysed.</p>
<p>On December 12, 2016, at approximately 9:36pm at night, my phone goes off with a text message telling me that Vela had glitched. The automated process I had set up wasn’t completely reliable – radio frequency interference (RFI) had been known to set it off in error. </p>
<p>So sceptically I logged in, and ran the test again. It was genuine! The excitement was incredible and I stayed up all night analysing the data.</p>
<p>What surfaced was quite surprising and not what was expected. Right as the glitch occurred, the pulsar missed a beat. It didn’t pulse. </p>
<p>The pulse before this “null” was broad and weird. Nothing like I’d ever seen or heard of before.</p>
<p>The two pulses following turned out to have no linear polarisation which was also unheard of for Vela. This meant the glitch had affected the strong magnet that drives the emission that comes from the pulsar.</p>
<p>Following the null, a train of 21 pulses arrived early and the variance in their timings was a lot smaller than normal – also very weird.</p>
<h2>The glitch explained, sort of</h2>
<p>So what causes glitches? The hypothesis that is best supported is that the neutron star has a hard crust and a superfluid core. The outer crust is what slows down, while the superfluid core rotates separately and does not slow down.</p>
<p>This is a very simplified explanation. What really happens is quite complex and involves microscopic superfluid vortices unpinning from the crust’s lattice.</p>
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Read more:
<a href="https://theconversation.com/stars-for-sale-but-no-you-cant-really-buy-an-official-star-name-to-remember-someone-92033">Stars for sale, but no, you can't really buy an official star name to remember someone</a>
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<p>After about three years the difference in rotation between the core and crust gets too great and the core “grips” the crust and speeds it up. The data seems to show that it took about five seconds for this speed-up to occur. This is on the faster end of the scale that the theorists had predicted. </p>
<p>All this and other information could help us understand what is called the “equation of state” – how matter behaves at different temperatures and pressures – in a laboratory that we simply cannot create here on Earth.</p>
<p>It also gives us, for the first time, a glimpse into the inside workings of a neutron star.</p><img src="https://counter.theconversation.com/content/94815/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jim Palfreyman received funding from the Australian Government Research Training Program Scholarship, which helped fund this research. </span></em></p>Pulsars are rapidly rotating neutron stars and some of them are know to have a “glitch”, and astronomers have captured one as it hapened.Jim Palfreyman, PhD candidate in astronomy, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/880832017-11-27T19:08:51Z2017-11-27T19:08:51ZFifty years ago Jocelyn Bell discovered pulsars and changed our view of the universe<figure><img src="https://images.theconversation.com/files/196451/original/file-20171127-2004-mbwiv5.jpg?ixlib=rb-1.1.0&rect=408%2C229%2C2555%2C1760&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">CSIRO Parkes radio telescope has discovered around half of all known pulsars. </span> <span class="attribution"><span class="source">Wayne England</span>, <span class="license">Author provided</span></span></figcaption></figure><p>A pulsar is a small, spinning star – a giant ball of neutrons, left behind after a normal star has died in a fiery explosion. </p>
<p>With a diameter of only 30 km, the star spins up to hundreds of times a second, while sending out a beam of radio waves (and sometimes other radiation, such as X-rays). When the beam is pointed in our direction and into our telescopes, we see a pulse.</p>
<p>2017 marks 50 years since pulsars were discovered. In that time, we have found more than 2,600 pulsars (mostly in the Milky Way), and used them to hunt for low-frequency gravitational waves, to determine the structure of our galaxy and to test the general theory of relativity. </p>
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Read more:
<a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">At last, we've found gravitational waves from a collapsing pair of neutron stars</a>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/gjLk_72V9Bw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What is a pulsar?</span></figcaption>
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<h2>The discovery</h2>
<p>In mid-1967, when thousands of people were enjoying the summer of love, a young PhD student at the University of Cambridge in the UK was helping to build a telescope.</p>
<p>It was a poles-and-wires affair – what astronomers call a “dipole array”. It covered a bit less than two hectares, the area of 57 tennis courts. </p>
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<img alt="" src="https://images.theconversation.com/files/196453/original/file-20171127-2038-s72xmq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/196453/original/file-20171127-2038-s72xmq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=926&fit=crop&dpr=1 600w, https://images.theconversation.com/files/196453/original/file-20171127-2038-s72xmq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=926&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/196453/original/file-20171127-2038-s72xmq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=926&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/196453/original/file-20171127-2038-s72xmq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1163&fit=crop&dpr=1 754w, https://images.theconversation.com/files/196453/original/file-20171127-2038-s72xmq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1163&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/196453/original/file-20171127-2038-s72xmq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1163&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">Jocelyn Bell Burnell, who discovered the first pulsar.</span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p>By July it was built. The student, Jocelyn Bell (now <a href="https://www.biography.com/people/jocelyn-bell-burnell-9206018">Dame Jocelyn Bell Burnell</a>), became responsible for running it and analysing the data it churned out. The data came in the form of pen-on-paper chart records, more than 30 metres of them each day. Bell analysed them by eye.</p>
<p>What she found – a little bit of “<a href="https://exhibitions.lib.cam.ac.uk/linesofthought/artifacts/bell-burnell/">scruff</a>” on the chart records – has gone down in history. </p>
<p>Like most discoveries, it took place over time. But there was a turning point. On November 28, 1967, Bell and her supervisor, <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1974/hewish-bio.html">Antony Hewish</a>, were able to capture a “fast recording” – that is, a detailed one – of one of the strange signals. </p>
<p>In this she could see for the first time that the “scruff” was actually a train of pulses spaced by one-and-a-third seconds. Bell and Hewish had discovered pulsars.</p>
<p>But this wasn’t immediately obvious to them. Following Bell’s observation they worked for two months to eliminate mundane explanations for the signals. </p>
<p>Bell also found another three sources of pulses, which helped to scotch some rather more exotic explanations, such as the idea that the signals came from “little green men” in extraterrestrial civilisations. The <a href="https://www.nature.com/articles/217709a0">discovery paper</a> appeared in Nature on February 24, 1968.</p>
<p>Later, Bell <a href="http://www.telegraph.co.uk/news/science/11941453/Female-physicist-overlooked-for-Nobel-Prize-finally-receives-recognition-as-Woman-of-the-Year.html">missed out</a> when Hewish and his colleague Sir Martin Ryle were awarded the 1974 Nobel Prize in Physics. </p>
<h2>A pulsar on ‘the pineapple’</h2>
<p>CSIRO’s Parkes radio telescope in Australia made its first observation of a pulsar in 1968, later made famous by appearing (along with the Parkes telescope) on the first Australian $50 note. </p>
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<img alt="" src="https://images.theconversation.com/files/196445/original/file-20171127-2021-1aoob8w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/196445/original/file-20171127-2021-1aoob8w.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=574&fit=crop&dpr=1 600w, https://images.theconversation.com/files/196445/original/file-20171127-2021-1aoob8w.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=574&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/196445/original/file-20171127-2021-1aoob8w.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=574&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/196445/original/file-20171127-2021-1aoob8w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=721&fit=crop&dpr=1 754w, https://images.theconversation.com/files/196445/original/file-20171127-2021-1aoob8w.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=721&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/196445/original/file-20171127-2021-1aoob8w.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=721&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">Australia’s first $50 note featured the Parkes telescope and a pulsar.</span>
<span class="attribution"><span class="license">Author provided</span></span>
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<p>Fifty years later, Parkes has found more than half of the known pulsars. The University of Sydney’s Molonglo Telescope also played a central role, and they both remain active in finding and timing pulsars today.</p>
<p>Internationally, one of the most exciting new instruments on the scene is China’s Five-hundred-metre Aperture Spherical Telescope, or <a href="http://www.skyandtelescope.com/astronomy-blogs/astronomy-space-david-dickinson/fast-worlds-largest-radio-telescope-open/">FAST</a>. FAST has recently found several new pulsars, confirmed by the Parkes telescope and a team of CSIRO astronomers working with their Chinese colleagues.</p>
<h2>Why look for pulsars?</h2>
<p>We want to understand what pulsars are, how they work, and how they fit into the general population of stars. The extreme cases of pulsars – those that are super fast, super slow, or extremely massive – help to limit the possible models for how pulsars work, telling us more about the structure of matter at ultra-high densities. To find these extreme cases, we need to find lots of pulsars. </p>
<p>Pulsars often orbit companion stars in binary systems, and the nature of these companions helps us understand the formation history of the pulsars themselves. We’ve made good progress with the “what” and “how” of pulsars but there are still unanswered questions.</p>
<p>As well as understanding pulsars themselves, we also use them as a clock. For example, pulsar timing is being pursued as a way to detect the background rumble of low-frequency gravitational waves throughout the universe.</p>
<p>Pulsars have also been used to measure the structure of our Galaxy, by looking at the way their signals are altered as they travel through denser regions of material in space.</p>
<p>Pulsars are also one of the finest tools we have for testing Einstein’s theory of general relativity. </p>
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Read more:
<a href="https://theconversation.com/explainer-einsteins-theory-of-general-relativity-3481">Explainer: Einstein's Theory of General Relativity</a>
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<p>This theory has survived 100 years of the most sophisticated tests astronomers have been able throw at it. But it doesn’t play nicely with our other most successful theory of how the universe works, <a href="https://theconversation.com/einstein-vs-quantum-mechanics-and-why-hed-be-a-convert-today-27641">quantum mechanics</a>, so it must have a tiny flaw somewhere. Pulsars help us to try and understand this problem. </p>
<p>What keeps pulsar astronomers up at night (literally!) is the hope of finding a pulsar in orbit around a black hole. This is the most extreme system we can imagine for testing general relativity. </p>
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<figcaption><span class="caption">Jocelyn Bell Burnell describes how she discovered pulsars.</span></figcaption>
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<p>Finally, pulsars have some more down-to-earth applications. We’re using them as a teaching tool in our <a href="https://www.csiro.au/en/Research/Astronomy/Astronomy-education-programs/PULSE-at-Parkes?ref=/CSIRO/Website/Education/Programs/Pulse-at-Parkes">PULSE@Parkes program</a>, in which students control the Parkes telescope over the Internet and use it to observe pulsars. This program has reached over 1,700 students, in Australia, Japan, China, The Netherlands, United Kingdom and South Africa. </p>
<p>Pulsars also offer promise as a navigation system for guiding craft travelling through deep space. In 2016 China launched a satellite, <a href="http://space.skyrocket.de/doc_sdat/xpnav-1.htm">XPNAV-1</a>, carrying a navigation system that uses periodic X-ray signals from certain pulsars.</p>
<p>Pulsars have changed our our understanding of the universe, and their true importance is still unfolding.</p><img src="https://counter.theconversation.com/content/88083/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>George Hobbs receives funding from the Australia Research Council</span></em></p><p class="fine-print"><em><span>Dick Manchester has received funding from the ARC.</span></em></p><p class="fine-print"><em><span>Simon Johnston 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>In mid 1967, PhD student Jocelyn Bell at Cambridge University was helping to build a telescope. She went on to discover a little bit of “scruff” - the first evidence of a pulsar.George Hobbs, Team leader for the Parkes Pulsar Timing Array project, CSIRORichard Manchester, CSIRO Fellow, CSIRO Astronomy and Space Science, CSIROSimon Johnston, Senior research scientist, CSIROLicensed as Creative Commons – attribution, no derivatives.