A gamma-ray pulsar milestone inspires innovative astrophysics and applications

The U.S. Naval Research Laboratory (NRL), in conjunction with the international Fermi Large Area Telescope Collaboration, announce the discovery of nearly 300 gamma ray pulsars in the publication of their Third Catalog of Gamma Ray Pulsars. This milestone comes 15 years since the launch of Fermi in 2008, when there were fewer than ten known gamma-ray pulsars.

"Work on this important catalog has been going on in our group for years," said Paul Ray, Ph.D., head of the High Energy Astrophysics and Applications Section at NRL.

"Our scientists and postdocs have been able to both discover and analyze the timing behavior and spectra of many of these newfound pulsars as part of our quest to further our understanding of these exotic stars that we are able to use as cosmic clocks."

Pulsars are formed when massive stars have burned though their fuel supply and become unable to resist the inward pull of their own gravity.

This results in the star collapsing into a dense, spinning magnetized neutron star.

Their spinning magnetic fields send out beams of gamma rays, the most energetic form of light.

As these beams sweep across the Earth, the highly sensitive Fermi gamma-ray telescope can observe their periodic pulses of energy.

With more than 15 years of data, Fermi has transformed the field of pulsar research.

"We have been very excited about how many millisecond pulsars (MSPs) we have been able to detect using these gamma rays," said Matthew Kerr, Ph.D., an NRL astrophysicist.

"We are able to study these objects that began as young pulsars in a binary system. Like a spinning top, they eventually slowed down and became inert. Over the past hundreds of millions of years, their binary companions dumped matter on to them, causing their speed to increase again, very dramatically and far faster than before, "recycling" these pulsars into MSPs. These high speed MSPs are now some of Nature's most precise timekeepers."

Scientists have been using these cosmic clocks in experiments called Pulsar Timing Arrays.

By searching for tiny deviations in the times at which the pulses arrive, scientist have been able to search for ripples in spacetime.

These ripples, known as gravitational waves, are produced when very massive objects, like pulsars, accelerate very quickly.

Very strong gravitational wave sources indicate a cataclysmic crash of dense, compact objects such as neutron stars and black holes.

Recently, several pulsar timing array collaborations, including several NRL researchers, published the first compelling evidence for very low-frequency gravitational waves, likely from the merger of supermassive black holes.

"These are such exciting results," said Thankful Cromartie, Ph.D., a National Research Council Research Associate at NRL.

"These low frequency gravitational waves allow us to peer into the centers of massive galaxies and better understand how they were formed."

The pulsar timing array results have important practical applications as well.

The spacetime distortions set a limit on how precisely we can use pulsars for critical navigation and timing.

In pulsar-based navigation, these spinning pulsars play much the same role as GPS satellites do, but we are able to use them far beyond the Earth's orbit.

"Now we know where that ultimate stability limit is," said Dr. Ray.

Using Fermi's gamma ray detection abilities are also having an impact on pulsar timing array work.

"Previously, once we found an MSP we had to hand it off to radio astronomers to monitor with huge telescopes," said Dr. Kerr.

"What we have found is that Fermi is sensitive enough by itself to constrain these gravitational waves and, unlike radio waves, which are bent like the light in a prism as they travel to earth, the gamma rays shoot straight to us. This reduces potential systemic errors in measurements."

For Megan DeCesar, Ph.D., a George Mason University scientist working at NRL, the most intriguing aspect of the new work in the dramatic increase of "spider" pulsars.

"Spider pulsars are named after arachnids that eat their smaller mates," DeCesar said.

"Something similar can happen when a neutron star and its binary companion are very close to each other and the MSP "recycling" process gets a little carried away. The intense radiation and particle wind from the pulsar eats away at the surface of the other star, resulting in a puffball of evaporated material."

When compared to radio observations, Fermi is particularly adept at finding these "spiders" as, in many cases, radio waves are eclipsed as the pulsar beam passes the remnants of the companion star.

Gamma rays, however, are capable of passing right through. "While it may be that spider systems are also intrinsically brighter in gamma rays, studying them will help us to understand their origins and the bonanza of discoveries we have made with Fermi," said DeCesar.

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Pulsars may make dark matter glow

The central question in the ongoing hunt for dark matter is: what is it made of? One possible answer is that dark matter consists of particles known as axions. A team of astrophysicists, led by researchers from the universities of Amsterdam and Princeton, has now shown that if dark matter consists of axions, it may reveal itself in the form of a subtle additional glow coming from pulsating stars.

Dark matter may be the most sought-for constituent of our universe. Surprisingly, this mysterious form of matter, that physicist and astronomers so far have not been able to detect, is assumed to make up an enormous part of what is out there. No less than 85% of matter in the universe is suspected to be 'dark', presently only noticeable through the gravitational pull it exerts on other astronomical objects. Understandably, scientists want more. They want to really see dark matter -- or at the very least, detect its presence directly, not just infer it from gravitational effects. And, of course: they want to know what it is.

Cleaning up two problems

One thing is clear: dark matter cannot be the same type of matter that you and I are made of. If that were to be the case, dark matter would simply behave like ordinary matter -- it would form objects like stars, light up, and no longer be 'dark'. Scientists are therefore looking for something new -- a type of particle that nobody has detected yet, and that probably only interacts very weakly with the types of particles that we know, explaining why this constituent of our world so far has remained elusive.

There are plenty of clues for where to look. One popular assumption is that dark matter could be made of axions. This hypothetical type of particle was first introduced in the 1970s to resolve a problem that had nothing to do with dark matter. The separation of positive and negative charges inside the neutron, one of the building blocks of ordinary atoms, turned out to be unexpectedly small. Scientists of course wanted to know why. It turned out that the presence of a hitherto undetected type of particle, interacting very weakly with the neutron's constituents, could cause exactly such an effect. The later Nobel Prize winner Frank Wilczek came up with a name for the new particle: axion -- not just similar to other particle names like proton, neutron, electron and photon, but also inspired by a laundry detergent of the same name. The axion was there to clean up a problem.

In fact, despite never being detected, it might clean up two. Several theories for elementary particles, including string theory, one of the leading candidate theories to unify all forces in nature, appeared to predict that axion-like particles could exist. If axions were indeed out there, could they also constitute part or even all of the missing dark matter? Perhaps, but an additional question that haunted all dark matter research was just as valid for axions: if so, then how can we see them? How does one make something 'dark' visible?

Shining a light on dark matter

Fortunately, it seems that for axions there may be a way out of this conundrum. If the theories that predict axions are correct, they are not only expected to be mass-produced in the universe, but some axions could also be converted into light in the presence of strong electromagnetic fields. Once there is light, we can see. Could this be the key to detect axions -- and therefore to detect dark matter?

To answer that question, scientists first had to ask themselves where in the universe the strongest known electric and magnetic fields occur. The answer is: in regions surrounding rotating neutron stars also known as pulsars. These pulsars -- short for 'pulsating stars' -- are dense objects, with a mass roughly the same as that of our Sun, but a radius that is around 100,000 times smaller, only about 10 km. Being so small, pulsars spin with enormous frequencies, emitting bright narrow beams of radio emission along their axis of rotation. Similar to a lighthouse, the pulsar's beams can sweep across the Earth, making the pulsating star easily observable.

However, the pulsar's enormous spin does more. It turns the neutron star into an extremely strong electromagnet. That, in turn, could mean that pulsars are very efficient axion factories. Every single second an average pulsar would be capable of producing a 50-digit number of axions. Because of the strong electromagnetic field around the pulsar, a fraction of these axions could convert into observable light. That is: if axions exist at all -- but the mechanism can now be used to answer just that question. Just look at pulsars, see if they emit extra light, and if they do, determine whether this extra light could be coming from axions.

Simulating a subtle glow

As always in science, actually performing such an observation is of course not that simple. The light emitted by axions -- detectable in the form of radio waves -- would only be a small fraction of the total light that these bright cosmic lighthouses send our way. One needs to know very precisely what a pulsar without axions would look like, and what a pulsar with axions would look like, to be able to see the difference -- let alone to quantify that difference and turn it into a measurement of an amount of dark matter.

This is exactly what a team of physicists and astronomers have now done. In a collaborative effort between the Netherlands, Portugal and the USA, the team has constructed a comprehensive theoretical framework which allows for the detailed understanding of how axions are produced, how axions escape the gravitational pull of the neutron star, and how, during their escape, they convert into low energy radio radiation.

The theoretical results were then put on a computer to model the production of axions around pulsars, using state-of-the-art numerical plasma simulations that were originally developed to understand the physics behind how pulsars emit radio waves. Once virtually produced, the propagation of the axions through the electromagnetic fields of the neutron star was simulated. This allowed the researchers to quantitatively understand the subsequent production of radio waves and model how this process would provide an additional radio signal on top of the intrinsic emission generated from the pulsar itself.

Putting axion models to a test

The results from theory and simulation were then put to a first observational test. Using observations from 27 nearby pulsars, the researchers compared the observed radio waves to the models, to see if any measured excess could provide evidence for the existence of axions. Unfortunately, the answer was 'no' -- or perhaps more optimistically: 'not yet'. Axions do not immediately jump out to us, but perhaps that was not to be expected. If dark matter were to give up its secrets that easily, it would already have been observed a long time ago.

The hope for a smoking-gun detection of axions, therefore, is now on future observations. Meanwhile, the current non-observation of radio signals from axions is an interesting result in itself. The first comparison between simulations and actual pulsars has placed the strongest limits to date on the interaction that axions can have with light.

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Scientists discover the highest energy gamma-rays ever from a pulsar

Scientists using the H.E.S.S. observatory in Namibia have detected the highest energy gamma rays ever from a dead star called a pulsar. The energy of these gamma rays clocked in at 20 tera-electronvolts, or about ten trillion times the energy of visible light. This observation is hard to reconcile with the theory of the production of such pulsed gamma rays, as the international team reports in the journal Nature Astronomy.

Pulsars are the left-over corpses of stars that spectacularly exploded in a supernova. The explosions leave behind a tiny, dead star with a diameter of just some 20 kilometres, rotating extremely fast and endowed with an enormous magnetic field. "These dead stars are almost entirely made up of neutrons and are incredibly dense: a teaspoon of their material has a mass of more than five billion tonnes, or about 900 times the mass of the Great Pyramid of Giza," explains H.E.S.S. scientist Emma de Oña Wilhelmi, a co-author of the publication working at DESY.

Pulsars emit rotating beams of electromagnetic radiation, somewhat like cosmic lighthouses. If their beam sweeps across our solar system, we see flashes of radiation at regular time intervals. These flashes, also called pulses of radiation, can be searched for in different energy bands of the electromagnetic spectrum. Scientists think that the source of this radiation are fast electrons produced and accelerated in the pulsar's magnetosphere, while traveling towards its periphery. The magnetosphere is made up of plasma and electromagnetic fields that surround and co-rotate with the star. "On their outward journey, the electrons acquire energy and release it in the form of the observed radiation beams," says Bronek Rudak from the Nicolaus Copernicus Astronomical Center (CAMK PAN) in Poland, also a co-author.

The Vela pulsar, located in the Southern sky in the constellation Vela (sail of the ship), is the brightest pulsar in the radio band of the electromagnetic spectrum and the brightest persistent source of cosmic gamma rays in the giga-electronvolts (GeV) range. It rotates about eleven times per second. However, above a few GeV, its radiation ends abruptly, presumably because the electrons reach the end of the pulsar's magnetosphere and escape from it.

But this is not the end of the story: using deep observations with H.E.S.S., a new radiation component at even higher energies has now been discovered, with energies of up to tens of tera-electronvolts (TeV). "That is about 200 times more energetic than all radiation ever detected before from this object," says co-author Christo Venter from the North-West University in South Africa. This very high-energy component appears at the same phase intervals as the one observed in the GeV range. However, to attain these energies, the electrons might have to travel even farther than the magnetosphere, yet the rotational emission pattern needs to remain intact.

"This result challenges our previous knowledge of pulsars and requires a rethinking of how these natural accelerators work," says Arache Djannati-Atai from the Astroparticle & Cosmology (APC) laboratory in France, who led the research. "The traditional scheme according to which particles are accelerated along magnetic field lines within or slightly outside the magnetosphere cannot sufficiently explain our observations. Perhaps we are witnessing the acceleration of particles through the so-called magnetic reconnection process beyond the light cylinder, which still somehow preserves the rotational pattern? But even this scenario faces difficulties to explain how such extreme radiation is produced."

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Telescopes help unravel pulsar puzzle

With a remarkable observational campaign that involved 12 telescopes both on the ground and in space, including three European Southern Observatory (ESO) facilities, astronomers have uncovered the strange behaviour of a pulsar, a super-fast-spinning dead star. This mysterious object is known to switch between two brightness modes almost constantly, something that until now has been an enigma. But astronomers have now found that sudden ejections of matter from the pulsar over very short periods are responsible for the peculiar switches.

"We have witnessed extraordinary cosmic events where enormous amounts of matter, similar to cosmic cannonballs, are launched into space within a very brief time span of tens of seconds from a small, dense celestial object rotating at incredibly high speeds," says Maria Cristina Baglio, researcher at New York University Abu Dhabi, affiliated with the Italian National Institute for Astrophysics (INAF), and the lead author of the paper published today in Astronomy & Astrophysics.

A pulsar is a fast-rotating, magnetic, dead star that emits a beam of electromagnetic radiation into space. As it rotates, this beam sweeps across the cosmos -- much like a lighthouse beam scanning its surroundings -- and is detected by astronomers as it intersects the line of sight to Earth. This makes the star appear to pulse in brightness as seen from our planet.

PSR J1023+0038, or J1023 for short, is a special type of pulsar with a bizarre behaviour. Located about 4500 light-years away in the Sextans constellation, it closely orbits another star. Over the past decade, the pulsar has been actively pulling matter off this companion, which accumulates in a disc around the pulsar and slowly falls towards it.

Since this process of accumulating matter began, the sweeping beam virtually vanished and the pulsar started incessantly switching between two modes. In the 'high' mode, the pulsar gives off bright X-rays, ultraviolet and visible light, while in the 'low' mode it's dimmer at these frequencies and emits more radio waves. The pulsar can stay in each mode for several seconds or minutes, and then switch to the other mode in just a few seconds. This switching has thus far puzzled astronomers.

"Our unprecedented observing campaign to understand this pulsar's behaviour involved a dozen cutting-edge ground-based and space-borne telescopes," says Francesco Coti Zelati, a researcher at the Institute of Space Sciences, Barcelona, Spain, and co-lead author of the paper. The campaign included ESO's Very Large Telescope (VLT) and ESO's New Technology Telescope (NTT), which detected visible and near-infrared light, as well as the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner. Over two nights in June 2021, they observed the system make over 280 switches between its high and low modes.

"We have discovered that the mode switching stems from an intricate interplay between the pulsar wind, a flow of high-energy particles blowing away from the pulsar, and matter flowing towards the pulsar," says Coti Zelati, who is also affiliated with INAF.

In the low mode, matter flowing towards the pulsar is expelled in a narrow jet perpendicular to the disc. Gradually, this matter accumulates closer and closer to the pulsar and, as this happens, it is hit by the wind blowing from the pulsating star, causing the matter to heat up. The system is now in a high mode, glowing brightly in the X-ray, ultraviolet and visible light. Eventually, blobs of this hot matter are removed by the pulsar via the jet. With less hot matter in the disc, the system glows less brightly, switching back into the low mode.

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Undead planets: The unusual conditions of the first exoplanet detection

The first ever exoplanets were discovered 30 years ago around a rapidly rotating star, called a pulsar. Now, astronomers have revealed that these planets may be incredibly rare. The new work will be presented tomorrow (Tuesday 12 July) at the National Astronomy Meeting (NAM 2022) by Iuliana Nițu, a PhD student at the University of Manchester.

The processes that cause planets to form, and survive, around pulsars are currently unknown. A survey of 800 pulsars followed by the Jodrell Bank Observatory over the last 50 years has revealed that this first detected exoplanet system may be extraordinarily uncommon: less than 0.5% of all known pulsars could host Earth-mass planets.

Pulsars are a type of neutron star, the densest stars in the universe, born during powerful explosions at the end of a typical star's life. They are exceptionally stable, rapidly rotating, and have incredibly strong magnetic fields. Pulsars emit beams of bright radio emission from their magnetic poles that appear to pulse as the star rotates.

"[Pulsars] produce signals which sweep the Earth every time they rotate, similarly to a cosmic lighthouse," says Nițu "These signals can then be picked up by radio telescopes and turned into a lot of amazing science."

In 1992, the first ever exoplanets were discovered orbiting a pulsar called PSR B1257+12. The planetary system is now known to host at least three planets similar in mass to the rocky planets in our Solar System. Since then, a handful of pulsars have been found to host planets. However, the extremely violent conditions surrounding the births and lives of pulsars make 'normal' planet formation unlikely, and many of these detected planets are exotic objects (such as planets made mostly of diamond) unlike those we know in our Solar System.

A team of astronomers at the University of Manchester performed the largest search for planets orbiting pulsars to date. In particular, the team looked for signals that indicate the presence of planetary companions with masses up to 100 times that of the Earth, and orbital time periods between 20 days and 17 years. Of the 10 potential detections, the most promising is the system PSR J2007+3120 with the possibility of hosting at least two planets, with masses a few times bigger than the Earth, and orbital periods of 1.9 and ~3.6 years.

The results of the work indicate no bias for particular planet masses or orbital periods in pulsar systems. However, the results do yield information of the shape of these planets' orbits: in contrast to the near-circular orbits found in our Solar System, these planets would orbit their stars on highly elliptical paths. This indicates that the formation process for pulsar-planet systems is vastly different than traditional star-planet systems.

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Proposed spacecraft navigation uses x-rays from dead stars

The remnants of a collapsed neutron star, called a pulsar, are magnetically charged and spinning anywhere from one rotation per second to hundreds of rotations per second. These celestial bodies, each 12 to 15 miles in diameter, generate light in the x-ray wavelength range. Researchers at The Grainger College of Engineering, University of Illinois Urbana-Champaign developed a new way spacecraft can use signals from multiple pulsars to navigate in deep space.

"We can use star trackers to determine the direction a spacecraft is pointing, but to learn the precise location of the spacecraft, we rely on radio signals sent between the spacecraft and the Earth, which can take a lot of time and requires use of oversubscribed infrastructure, like NASA's Deep Space Network," said Zach Putnam, professor in the Department of Aerospace Engineering at Illinois.

"Using x-ray navigation eliminates those two factors, but until now, required an initial position estimate of the spacecraft as a starting point. This research presents a system that finds candidates for possible spacecraft locations without prior information, so the spacecraft can navigate autonomously."

"Also, our ground communication systems for deep space missions are overloaded right now," he said. "This system would give spacecraft autonomy and reduce the dependency on the ground. X-ray pulsar navigation gets us around that and allows us to determine where we are, without calling."

Putnam said because our atmosphere filters out all the x-rays, you have to be in space to observe them. The pulsars emit electromagnetic radiation that look like pulses because we measure the peak in the x-ray signals every time the pulsar spins around and points toward us -- like the ray of light cast from the beacon on a lighthouse.

"Each pulsar has its own characteristic signal, like a fingerprint," he said. "We have records of the x-rays over time from the 2,000 or so pulsars and how they've changed over time."

Much like the Global Positioning System, location can be determined from intersection of three signals.

"The issue with pulsars is that they spin so fast that the signal repeats itself a lot," he said. "By comparison, GPS repeats every two weeks. With pulsars, while there are an infinite number of possible spacecraft locations, we know how far apart these candidate locations are from each other.

"We are looking at determining spacecraft position within domains that have diameters on the order of multiple astronomical units, like the size of the orbit of Jupiter -- something like a square with one billion miles on a side. The challenge we are trying to address is, how do we intelligently observe pulsars and fully determine all possible spacecraft locations in a domain without using an excessive amount of compute resources," Putnam said.

The algorithm developed by graduate student Kevin Lohan combines observations from numerous pulsars to determine all the possible positions of the spacecraft. The algorithm processes all the candidate intersections in two dimensions or three dimensions.

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Cosmic 'spider' found to be source of powerful gamma-rays

Using the 4.1-meter SOAR Telescope in Chile, astronomers have discovered the first example of a binary system where a star in the process of becoming a white dwarf is orbiting a neutron star that has just finished turning into a rapidly spinning pulsar. The pair, originally detected by the Fermi Gamma-ray Space Telescope, is a "missing link" in the evolution of such binary systems.

A bright, mysterious source of gamma rays has been found to be a rapidly spinning neutron star -- dubbed a millisecond pulsar -- that is orbiting a star in the process of evolving into an extremely-low-mass white dwarf. These types of binary systems are referred to by astronomers as "spiders" because the pulsar tends to "eat" the outer parts of the companion star as it turns into a white dwarf.

The duo was detected by astronomers using the 4.1-meter SOAR Telescope on Cerro Pachón in Chile, part of Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF's NOIRLab.

NASA's Fermi Gamma-ray Space Telescope has been cataloging objects in the Universe that produce copious gamma rays since its launch in 2008, but not all of the sources of gamma rays that it detects have been classified. One such source, called 4FGL J1120.0-2204 by astronomers, was the second brightest gamma-ray source in the entire sky that had gone unidentified, until now.

Astronomers from the United States and Canada, led by Samuel Swihart of the US Naval Research Laboratory in Washington, D.C., used the Goodman Spectrograph on the SOAR Telescope to determine the true identity of 4FGL J1120.0-2204. The gamma-ray source, which also emits X-rays, as observed by NASA's Swift and ESA's XMM-Newton space telescopes, has been shown to be a binary system consisting of a "millisecond pulsar" that spins hundreds of times per second, and the precursor to an extremely-low-mass white dwarf. The pair are located over 2600 light-years away.

"Michigan State University's dedicated time on the SOAR Telescope, its location in the southern hemisphere and the precision and stability of the Goodman spectrograph, were all important aspects of this discovery," says Swihart.

"This is a great example of how mid-sized telescopes in general, and SOAR in particular, can be used to help characterize unusual discoveries made with other ground and space-based facilities," notes Chris Davis, NOIRLab Program Director at US National Science Foundation. "We anticipate that SOAR will play a crucial role in the follow-up of many other time-variable and multi-messenger sources over the coming decade."

The optical spectrum of the binary system measured by the Goodman spectrograph showed that light from the proto-white dwarf companion is Doppler shifted -- alternately shifted to the red and the blue -- indicating that it orbits a compact, massive neutron star every 15 hours.

"The spectra also allowed us to constrain the approximate temperature and surface gravity of the companion star," says Swihart, whose team was able to take these properties and apply them to models describing how binary star systems evolve. This allowed them to determine that the companion is the precursor to an extremely-low-mass white dwarf, with a surface temperature of 8200 °C (15,000 °F), and a mass of just 17% that of the Sun.

When a star with a mass similar to that of the Sun or less reaches the end of its life, it will run out of the hydrogen used to fuel the nuclear fusion processes in its core. For a time, helium takes over and powers the star, causing it to contract and heat up, and prompting its expansion and evolution into a red giant that is hundreds of millions of kilometers in size. Eventually, the outer layers of this swollen star can be accreted onto a binary companion and nuclear fusion halts, leaving behind a white dwarf about the size of Earth and sizzling at temperatures exceeding 100,000 °C (180,000 °F).

The proto-white dwarf in the 4FGL J1120.0-2204 system hasn't finished evolving yet. "Currently it's bloated, and is about five times larger in radius than normal white dwarfs with similar masses," says Swihart. "It will continue cooling and contracting and, in about two billion years, it will look identical to many of the extremely low mass white dwarfs that we already know about."

Millisecond pulsars twirl hundreds of times every second. They are spun up by accreting matter from a companion, in this case from the star that became the white dwarf. Most millisecond pulsars emit gamma rays and X-rays, often when the pulsar wind, which is a stream of charged particles emanating from the rotating neutron star, collides with material emitted from a companion star.

About 80 extremely low-mass white dwarfs are known, but "this is the first precursor to an extremely low-mass white dwarf found that is likely orbiting a neutron star," says Swihart. Consequently, 4FGL J1120.0-2204 is a unique look at the tail-end of this spin-up process. All the other white dwarf-pulsar binaries that have been discovered are well past the spinning-up stage.

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Challenging Einstein’s greatest theory with extreme stars

Researchers at the University of East Anglia and the University of Manchester have helped conduct a 16-year long experiment to challenge Einstein's theory of general relativity.

The international team looked to the stars -- a pair of extreme stars called pulsars to be precise -- through seven radio telescopes across the globe.

And they used them to challenge Einstein's most famous theory with some of the most rigorous tests yet.

The study, published today in the journal Physical Review X, reveals new relativistic effects that, although expected, have now been observed for the first time.

Dr Robert Ferdman, from UEA's School of Physics, said: "As spectacularly successful as Einstein's theory of general relativity has proven to be, we know that is not the final word in gravitational theory.

"More than 100 years later, scientists around the world continue their efforts to find flaws in his theory.

"General relativity is not compatible with the other fundamental forces, described by quantum mechanics. It is therefore important to continue to place the most stringent tests upon general relativity as possible, to discover how and when the theory breaks down.

"Finding any deviation from general relativity would constitute a major discovery that would open a window on new physics beyond our current theoretical understanding of the Universe.

"And it may help us toward eventually discovering a unified theory of the fundamental forces of nature."

Led by Michael Kramer from the Max Planck Institute for Radio Astronomy in Bonn, Germany, the international team of researchers from ten countries, put Einstein's theory to the most rigorous tests yet.

Dr Ferdman said: "A pulsar is a highly magnetised rotating compact star that emits beams of electromagnetic radiation out of its magnetic poles.

"They weigh more than our sun but they are only about 15 miles across -- so they are incredibly dense objects that produce radio beams that sweep the sky like a lighthouse.

"We studied a double pulsar, which was discovered by members of the team in 2003 and presents the most precise laboratory we currently have to test Einstein's theory. Of course, his theory was conceived when neither these types of extreme stars, nor the techniques used to study them, could be imagined."

The double pulsar consists of two pulsars which orbit each other in just 147 minutes with velocities of about 1 million km/h. One pulsar is spinning very fast, about 44 times a second. The companion is young and has a rotation period of 2.8 seconds. It is their motion around each other which can be used as a near perfect gravity laboratory.

Seven sensitive radio telescopes were used to observe this double pulsar -- in Australia, the US, France, Germany, the Netherlands and in the UK (the Lovell Radio Telescope).

Prof Kramer said: "We studied a system of compact stars that is an unrivalled laboratory to test gravity theories in the presence of very strong gravitational fields.

"To our delight we were able to test a cornerstone of Einstein's theory, the energy carried by gravitational waves, with a precision that is 25 times better than with the Nobel-Prize winning Hulse-Taylor pulsar, and 1000 times better than currently possible with gravitational wave detectors."

He explained that the observations are not only in agreement with the theory, "but we were also able to see effects that could not be studied before''.

Prof Benjamin Stappers, from the University of Manchester, said: "The discovery of the double pulsar system was made as part of a survey co-led from the University of Manchester and presented us with the only known instance of two cosmic clocks which allow precise measurement of the structure and evolution of an intense gravitational field.

"The Lovell Telescope at the Jodrell Bank Observatory has been monitoring it every couple of weeks since then. This long baseline of high quality and frequent observations provided an excellent data set to be combined with those from observatories around the world."

Prof Ingrid Stairs from the University of British Columbia at Vancouver, said: "We follow the propagation of radio photons emitted from a cosmic lighthouse, a pulsar, and track their motion in the strong gravitational field of a companion pulsar.

"We see for the first time how the light is not only delayed due to a strong curvature of spacetime around the companion, but also that the light is deflected by a small angle of 0.04 degrees that we can detect. Never before has such an experiment been conducted at such a high spacetime curvature."

Prof Dick Manchester from Australia's national science agency, CSIRO, said: "Such fast orbital motion of compact objects like these -- they are about 30 per cent more massive than the Sun but only about 24 km across -- allows us to test many different predictions of general relativity -- seven in total!

"Apart from gravitational waves and light propagation, our precision allows us also to measure the effect of "time dilation" that makes clocks run slower in gravitational fields.

"We even need to take Einstein's famous equation E = mc2 into account when considering the effect of the electromagnetic radiation emitted by the fast-spinning pulsar on the orbital motion.

"This radiation corresponds to a mass loss of 8 million tonnes per second! While this seems a lot, it is only a tiny fraction -- 3 parts in a thousand billion billion(!) -- of the mass of the pulsar per second."

The researchers also measured -- with a precision of 1 part in a million(!) -- that the orbit changes its orientation, a relativistic effect also well known from the orbit of Mercury, but here 140,000 times stronger.

They realised that at this level of precision they also need to consider the impact of the pulsar's rotation on the surrounding spacetime, which is "dragged along" with the spinning pulsar.

Dr Norbert Wex from the MPIfR, another main author of the study, said: "Physicists call this the Lense-Thirring effect or frame-dragging. In our experiment it means that we need to consider the internal structure of a pulsar as a neutron star.

"Hence, our measurements allow us for the first time to use the precision tracking of the rotations of the neutron star, a technique that we call pulsar timing to provide constraints on the extension of a neutron star."

The technique of pulsar timing was combined with careful interferometric measurements of the system to determine its distance with high resolution imaging, resulting in a value of 2400 light years with only 8 per cent error margin.

Team member Prof Adam Deller, from Swinburne University in Australia and responsible for this part of the experiment, said: "It is the combination of different complementary observing techniques that adds to the extreme value of the experiment. In the past similar studies were often hampered by the limited knowledge of the distance of such systems."

This is not the case here, where in addition to pulsar timing and interferometry also the information gained from effects due to the interstellar medium were carefully taken into account.

Prof Bill Coles from the University of California San Diego agrees: "We gathered all possible information on the system and we derived a perfectly consistent picture, involving physics from many different areas, such as nuclear physics, gravity, interstellar medium, plasma physics and more. This is quite extraordinary."

Paulo Freire, also from MPIfR, said: "Our results are nicely complementary to other experimental studies which test gravity in other conditions or see different effects, like gravitational wave detectors or the Event Horizon Telescope.

"They also complement other pulsar experiments, like our timing experiment with the pulsar in a stellar triple system, which has provided an independent and superb test of the universality of free fall."

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Chandra X-ray Observatory studies extraordinary magnetar

 In 2020, astronomers added a new member to an exclusive family of exotic objects with the discovery of a magnetar. New observations from NASA's Chandra X-ray Observatory help support the idea that it is also a pulsar, meaning it emits regular pulses of light.

Magnetars are a type of neutron star, an incredibly dense object mainly made up of tightly packed neutron, which forms from the collapsed core of a massive star during a supernova.

What sets magnetars apart from other neutron stars is that they also have the most powerful known magnetic fields in the universe. For context, the strength of our planet's magnetic field has a value of about one Gauss, while a refrigerator magnet measures about 100 Gauss. Magnetars, on the other hand, have magnetic fields of about a million billion Gauss. If a magnetar was located a sixth of the way to the Moon (about 40,000 miles), it would wipe the data from all of the credit cards on Earth.

On March 12, 2020, astronomers detected a new magnetar with NASA's Neil Gehrels Swift Telescope. This is only the 31st known magnetar, out of the approximately 3,000 known neutron stars.

After follow-up observations, researchers determined that this object, dubbed J1818.0-1607, was special for other reasons. First, it may be the youngest known magnetar, with an age estimated to be about 500 years old. This is based on how quickly the rotation rate is slowing and the assumption that it was born spinning much faster. Secondly, it also spins faster than any previously discovered magnetar, rotating once around every 1.4 seconds.

Chandra's observations of J1818.0-1607 obtained less than a month after the discovery with Swift gave astronomers the first high-resolution view of this object in X-rays. The Chandra data revealed a point source where the magnetar was located, which is surrounded by diffuse X-ray emission, likely caused by X-rays reflecting off dust located in its vicinity. (Some of this diffuse X-ray emission may also be from winds blowing away from the neutron star.)

Harsha Blumer of West Virginia University and Samar Safi-Harb of the University of Manitoba in Canada recently published results from the Chandra observations of J1818.0-1607 in The Astrophysical Journal Letters.

This composite image contains a wide field of view in the infrared from two NASA missions, the Spitzer Space Telescope and the Wide-Field Infrared Survey Explorer (WISE), taken before the magnetar's discovery. X-rays from Chandra show the magnetar in purple. The magnetar is located close to the plane of the Milky Way galaxy at a distance of about 21,000 light-years from Earth.

Other astronomers have also observed J1818.0-1607 with radio telescopes, such as the NSF's Karl Jansky Very Large Array (VLA), and determined that it gives off radio waves. This implies that it also has properties similar to that of a typical "rotation-powered pulsar," a type of neutron star that gives off beams of radiation that are detected as repeating pulses of emission as it rotates and slows down. Only five magnetars including this one have been recorded to also act like pulsars, constituting less than 0.2% of the known neutron star population.

The Chandra observations may also provide support for this general idea. Safi-Harb and Blumer studied how efficiently J1818.0-1607 is converting energy from its decreasing rate of spin into X-rays. They concluded this efficiency is lower than that typically found for magnetars, and likely within the range found for other rotation-powered pulsars.

The explosion that created a magnetar of this age would be expected to have left behind a detectable debris field. To search for this supernova remnant, Safi-Harb and Blumer looked at the X-rays from Chandra, infrared data from Spitzer, and the radio data from the VLA. Based on the Spitzer and VLA data they found possible evidence for a remnant, but at a relatively large distance away from the magnetar. In order to cover this distance the magnetar would need to have traveled at speeds far exceeding those of the fastest known neutron stars, even assuming it is much older than expected, which would allow more travel time.

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Measurements of pulsar acceleration reveal Milky Way's dark side

 

Milky Way in the night sky.

It is well known that the expansion of the universe is accelerating due to a mysterious dark energy. Within galaxies, stars also experience an acceleration, though this is due to some combination of dark matter and the stellar density. In a new study to be published in Astrophysical Journal Letters, researchers have now obtained the first direct measurement of the average acceleration taking place within our home galaxy, the Milky Way.

Led by Sukanya Chakrabarti at the Institute for Advanced Study with collaborators from Rochester Institute of Technology, University of Rochester, and University of Wisconsin-Milwaukee, the team used pulsar data to clock the radial and vertical accelerations of stars within and outside of the galactic plane. Based on these new high-precision measurements and the known amount of visible matter in the galaxy, researchers were then able to calculate the Milky Way's dark matter density without making the usual assumption that the galaxy is in a steady-state.

"Our analysis not only gives us the first measurement of the tiny accelerations experienced by stars in the galaxy, but also opens up the possibility of extending this work to understand the nature of dark matter, and ultimately dark energy on larger scales," stated Chakrabarti, the paper's lead author and a current Member and IBM Einstein Fellow at the Institute for Advanced Study.

Stars hurtle through the galaxy at hundreds of kilometers per second, yet this study indicates that the change in their velocities is occurring at a literal snail's pace -- a few centimeters per second, which is about the same speed as a crawling baby. To detect this subtle motion the research team relied on the ultraprecise time-keeping ability of pulsars that are widely distributed throughout the galactic plane and halo -- a diffuse spherical region that surrounds the galaxy.

"By exploiting the unique properties of pulsars, we were able to measure very small accelerations in the Galaxy. Our work opens a new window in galactic dynamics," said co-author Philip Chang of the University of Wisconsin-Milwaukee.

Extending outwards approximately 300,000 light years from the galactic center, the halo may provide important hints to understanding dark matter, which accounts for about 90 percent of the galaxy's mass and is highly concentrated above and below the star-dense galactic plane. Stellar motion in this particular region -- a primary focus of this study -- can be influenced by dark matter. Utilizing the local density measurements obtained through this study, researchers will now have a better idea of how and where to look for dark matter.

While previous studies assumed a state of galactic equilibrium to calculate average mass density, this research is based on the natural, non-equilibrium state of the galaxy. One might analogize this to the difference between the surface of a pond before and after a stone is tossed in. By accounting for the "ripples" the team was able to obtain a more accurate picture of reality. Though in this case, rather than stones, the Milky Way is influenced by a turbulent history of galactic mergers and continues to be perturbed by external dwarf galaxies like the Small and Large Magellanic Clouds. As a result, stars do not have flat orbits and tend to follow a path similar to that of a warped vinyl record, crossing above and below the galactic plane. One of the key factors that enabled this direct observational approach was the use of pulsar data compiled from international collaborations, including NANOGrav (North American Nanohertz Observatory for Gravitational Waves) that has obtained data from the Green Bank and Arecibo telescopes.

This landmark paper expands upon the work of Jan H. Oort (1932); John Bahcall (1984); Kuijken & Gilmore (1989); Holmberg & Flynn (2000); Jo Bovy & Scott Tremaine (2012) to calculate the average mass density in the galactic plane (Oort limit) and local dark matter density. IAS scholars including Oort, Bahcall, Bovy, Tremaine, and Chakrabarti have played an important role in advancing this area of research.

"For centuries astronomers have measured the positions and speeds of stars, but these provide only a snapshot of the complex dynamical behavior of the Milky Way galaxy," stated Scott Tremaine, Professor Emeritus at the Institute for Advanced Study. "The accelerations measured by Chakrabarti and her collaborators are directly caused by the gravitational forces from the matter in the galaxy, both visible and dark, and thereby provide a new and promising window on the distribution and the composition of the matter in the galaxy and the universe."

This particular paper will enable a wide variety of future studies. Accurate measurements of accelerations will also soon be possible using the complementary radial velocity method that Chakrabarti developed earlier this year, which measures the change in the velocity of stars with high precision. This work will also enable more detailed simulations of the Milky Way, improve constraints on general relativity, and provide clues in the search for dark matter. Extensions of this method may ultimately allow us to directly measure the cosmic acceleration as well.

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Researchers find 'missing link' between magnetars and rotation-powered pulsars

 Researchers from the RIKEN Cluster for Pioneering Research have made observations of a new magnetar, called Swift J1818.0-1607, which challenges current knowledge about two types of extreme stars, known as magnetars and pulsars. The research, just published in The Astrophysical Journal, was done using the Neutron star Interior Composition Explorer (NICER), an X-ray instrument aboard the International Space Station. Magnetars are a subtype of pulsars, which are neutron stars -- degenerate stars that failed to become black holes but instead became extremely dense bodies composed mostly of neutrons. Magnetars as well as some young rotation-powered pulsars -- another type of pulsar -- emit powerful X-ray beams, but the mechanism is believed to be different. With magnetars, the beams are believed to be powered by extremely strong magnetic fields, whereas in canonical pulsars they are powered by the rapid rotation of the star. However, there is much that is not well understood about these phenomena. Recently, several magnetars have been shown to emit radio waves -- a property that was formerly thought to be limited to canonical rotation-powered pulsars -- blurring the boundary between the two.

For the current study, work done by Chin-Ping Hu, a visiting researcher at the Extreme Natural Phenomena RIKEN Hakubi Research Team in the RIKEN Cluster for Pioneering Research and colleagues, has revealed a missing link between the two types of pulsar.

On March 12, a new gamma-ray burst was detected by the Burst Alert Telescope (BAT) aboard the Neil Gehrels Swift Observatory, a space-based gamma ray observatory. The object, believed to be a magnetar, was dubbed Swift J1818.0-1607. The RIKEN group and NICER team quickly moved into action. Four hours after the alert, they began making X-ray follow-up observations with NICER.

They found that the magnetar had a pulsation period of 1.36 seconds, the shortest among magnetars observed until now. Their observations showed that it was showing spin-down behavior -- suggesting that the emissions were to some extent being powered by rotations -- and that it had a magnetar-level surface magnetic field of 2.7×1014 Gauss, indicating that it is a young magnetar, formed about 420 years earlier. Studies of "glitches" -- sudden changes in the rotational frequency that are important of understanding neutron stars -- as well as the noisy timing behavior of its stellar rotation showed that it is indeed young. However, its X-ray emission was found to be lower than that of other magnetars, indicating that the star has attributes of both magnetars and rotation powered pulsars.

According to Hu, "Our study has given us new understanding of the neutron stars with high magnetic fields. Recent radio observations suggest that magnetars may be a cause of mysterious phenomena called fast radio bursts, so we look forward to investigating further."

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How colliding neutron stars could shed light on universal mysteries

An important breakthrough in how we can understand dead star collisions and the expansion of the Universe has been made by an international team, led by the University of East Anglia.

They have discovered an unusual pulsar -- one of deep space's magnetized spinning neutron-star 'lighthouses' that emits highly focused radio waves from its magnetic poles.

The newly discovered pulsar (known as PSR J1913+1102) is part of a binary system -- which means that it is locked in a fiercely tight orbit with another neutron star.

Neutron stars are the dead stellar remnants of a supernova. They are made up of the most dense matter known -- packing hundreds of thousands of times the Earth's mass into a sphere the size of a city.

In around half a billion years the two neutron stars will collide, releasing astonishing amounts of energy in the form of gravitational waves and light.

But the newly discovered pulsar is unusual because the masses of its two neutron stars are quite different -- with one far larger than the other.

This asymmetric system gives scientists confidence that double neutron star mergers will provide vital clues about unsolved mysteries in astrophysics -- including a more accurate determination of the expansion rate of the Universe, known as the Hubble constant.

The discovery, published today in the journal Nature, was made using the Arecibo radio telescope in Puerto Rico.

Lead researcher Dr Robert Ferdman, from UEA's School of Physics, said: "Back in 2017, scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) first detected the merger of two neutron stars.

"The event caused gravitational-wave ripples through the fabric of space time, as predicted by Albert Einstein over a century ago."

Known as GW170817, this spectacular event was also seen with traditional telescopes at observatories around the world, which identified its location in a distant galaxy, 130 million light years from our own Milky Way.

Dr Ferdman said: "It confirmed that the phenomenon of short gamma-ray bursts was due to the merger of two neutron stars. And these are now thought to be the factories that produce most of the heaviest elements in the Universe, such as gold."

The power released during the fraction of a second when two neutron stars merge is enormous -- estimated to be tens of times larger than all stars in the Universe combined.

So the GW170817 event was not surprising. But the enormous amount of matter ejected from the merger and its brightness was an unexpected mystery.

Dr Ferdman said: "Most theories about this event assumed that neutron stars locked in binary systems are very similar in mass.

"Our new discovery changes these assumptions. We have uncovered a binary system containing two neutron stars with very different masses.

"These stars will collide and merge in around 470 million years, which seems like a long time, but it is only a small fraction of the age of the Universe.

"Because one neutron star is significantly larger, its gravitational influence will distort the shape of its companion star -- stripping away large amounts of matter just before they actually merge, and potentially disrupting it altogether.

"This 'tidal disruption' ejects a larger amount of hot material than expected for equal-mass binary systems, resulting in a more powerful emission.

"Although GW170817 can be explained by other theories, we can confirm that a parent system of neutron stars with significantly different masses, similar to the PSR J1913+1102 system, is a very plausible explanation.

"Perhaps more importantly, the discovery highlights that there are many more of these systems out there -- making up more than one in 10 merging double neutron star binaries."

Co-author Dr Paulo Freire from the Max Planck Institute for Radio Astronomy in Bonn, Germany, said: "Such a disruption would allow astrophysicists to gain important new clues about the exotic matter that makes up the interiors of these extreme, dense objects.

"This matter is still a major mystery -- it's so dense that scientists still don't know what it is actually made of. These densities are far beyond what we can reproduce in Earth-based laboratories."

The disruption of the lighter neutron star would also enhance the brightness of the material ejected by the merger. This means that along with gravitational-wave detectors such as the US-based LIGO and the Europe-based Virgo detector, scientists will also be able to observe them with conventional telescopes.

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Astronomers capture a pulsar 'powering up'

The research, led by PhD candidate Adelle Goodwin from the Monash School of Physics and Astronomy will be featured at an upcoming American Astronomical Society meeting this week before it is published in Monthly Notices of the Royal Astronomical Society. Adelle leads a team of international researchers, including her supervisor, Monash University Associate Professor Duncan Galloway, and Dr David Russell from New York University Abu Dhabi.

The scientists observed an 'accreting' neutron star as it entered an outburst phase in an international collaborative effort involving five groups of researchers, seven telescopes (five on the ground, two in space), and 15 collaborators.

It is the first time such an event has been observed in this detail -- in multiple frequencies, including high-sensitivity measurements in both optical and X-ray.

The physics behind this 'switching on' process has eluded physicists for decades, partly because there are very few comprehensive observations of the phenomenon.

The researchers caught one of these accreting neutron star systems in the act of entering outburst, revealing that it took 12 days for material to swirl inwards and collide with the neutron star, substantially longer than the two- to three-days most theories suggest.

"These observations allow us to study the structure of the accretion disk, and determine how quickly and easily material can move inwards to the neutron star," Adelle said.

"Using multiple telescopes that are sensitive to light in different energies we were able to trace that the initial activity happened near the companion star, in the outer edges of the accretion disk, and it took 12 days for the disk to be brought into the hot state and for material to spiral inward to the neutron star, and X-rays to be produced," she said.

In an 'accreting' neutron star system, a pulsar (a dense remnant of an old star) strips material away from a nearby star, forming an accretion disk of material spiralling in towards the pulsar, where it releases extraordinary amounts of energy -- about the total energy output of the sun in 10 years, over the period of a few short weeks.

The pulsar observed is SAX J1808.4−3658 which rotates at a rapid 400 times per second and is located 11,000 light-years away in the constellation Saggitarius.

"This work enables us to shed some light on the physics of accreting neutron star systems, and to understand how these explosive outbursts are triggered in the first place, which has puzzled astronomers for a long time," said New York University Abu Dhabi researcher, Dr David Russell, one of the study's co-authors.

Accretion disks are usually made of hydrogen, but this particular object has a disk that is made up of 50% helium, more helium than most disks. The scientists think that this excess helium may be slowing down the heating of the disk because helium 'burns' at a higher temperature, causing the 'powering up' to take 12 days.

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New telescope design could capture distant celestial objects with unprecedented detail

Researchers have designed a new camera that could allow hypertelescopes to image multiple stars at once. The enhanced telescope design holds the potential to obtain extremely high-resolution images of objects outside our solar system, such as planets, pulsars, globular clusters and distant galaxies.

"A multi-field hypertelescope could, in principle, capture a highly detailed image of a star, possibly also showing its planets and even the details of the planets' surfaces," said Antoine Labeyrie, emeritus professor at the Collège de France and Observatoire de la Cote d'Azur, who pioneered the hypertelescope design. "It could allow planets outside of our solar system to be seen with enough detail that spectroscopy could be used to search for evidence of photosynthetic life."

In The Optical Society's (OSA) journal Optics Letters, Labeyrie and a multi-institutional group of researchers report optical modeling results that verify that their multi-field design can substantially extend the narrow field-of-view coverage of hypertelescopes developed to date.

Making the mirror larger

Large optical telescopes use a concave mirror to focus light from celestial sources. Although larger mirrors can produce more detailed pictures because of their reduced diffractive spreading of the light beam, there is a limit to how large these mirrors can be made. Hypertelescopes are designed to overcome this size limitation by using large arrays of mirrors, which can be spaced widely apart.

Researchers have previously experimented with relatively small prototype hypertelescope designs, and a full-size version is currently under construction in the French Alps. In the new work, researchers used computer models to create a design that would give hypertelescopes a much larger field of view. This design could be implemented on Earth, in a crater of the moon or even on an extremely large scale in space.

Building a hypertelescope in space, for example, would require a large flotilla of small mirrors spaced out to form a very large concave mirror. The large mirror focuses light from a star or other celestial object onto a separate spaceship carrying a camera and other necessary optical components.

"The multi-field design is a rather modest addition to the optical system of a hypertelescope, but should greatly enhance its capabilities," said Labeyrie. "A final version deployed in space could have a diameter tens of times larger than the Earth and could be used to reveal details of extremely small objects such as the Crab pulsar, a neutron star believed to be only 20 kilometers in size."

Expanding the view

Hypertelescopes use what is known as pupil densification to concentrate light collection to form high-resolution images. This process, however, greatly limits the field of view for hypertelescopes, preventing the formation of images of diffuse or large objects such as a globular star cluster, exoplanetary system or galaxy.

The researchers developed a micro-optical system that can be used with the focal camera of the hypertelescope to simultaneously generate separate images of each field of interest. For star clusters, this makes it possible to obtain separate images of each of thousands of stars simultaneously.

The proposed multi-field design can be thought of as an instrument made of multiple independent hypertelescopes, each with a differently tilted optical axis that gives it a unique imaging field. These independent telescopes focus adjacent images onto a single camera sensor.

The researchers used optical simulation software to model different implementations of a multi-field hypertelescope. These all provided accurate results that confirmed the feasibility of multi-field observations.

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Unprecedented detail in pulsar 6,500 light-years from Earth

The pulsar PSR B1957+20 is seen in the background through the cloud of gas enveloping its brown dwarf star companion.

A team of astronomers has performed one of the highest resolution observations in astronomical history by observing two intense regions of radiation, 20 kilometres apart, around a star 6500 light-years away.

The observation is equivalent to using a telescope on Earth to see a flea on the surface of Pluto.

The extraordinary observation was made possible by the rare geometry and characteristics of a pair of stars orbiting each other. One is a cool, lightweight star called a brown dwarf, which features a "wake" or comet-like tail of gas. The other is an exotic, rapidly spinning star called a pulsar.

"The gas is acting as like a magnifying glass right in front of the pulsar," says Robert Main, lead author of the paper describing the observation being published May 24 in the journal Nature. "We are essentially looking at the pulsar through a naturally occurring magnifier which periodically allows us to see the two regions separately."

Main is a PhD astronomy student in the Department of Astronomy & Astrophysics at the University of Toronto, working with colleagues at the University of Toronto's Dunlap Institute for Astronomy & Astrophysics and Canadian Institute for Theoretical Astrophysics, and the Perimeter Institute.

The pulsar is a neutron star that rotates rapidly -- over 600 times a second. As the pulsar spins, it emits beams of radiation from the two hotspots on its surface. The intense regions of radiation being observed are associated with the beams.

The brown dwarf star is about a third the diameter of the Sun. It is roughly two million kilometres from the pulsar -- or five times the distance between the Earth and the moon -- and orbits around it in just over 9 hours. The dwarf companion star is tidally locked to the pulsar so that one side always faces its pulsating companion, the way the moon is tidally locked to the Earth.

Because it is so close to the pulsar, the brown dwarf star is blasted by the strong radiation coming from its smaller companion. The intense radiation from the pulsar heats one side of the relatively cool dwarf star to the temperature of our Sun, or some 6000°C.

The blast from the pulsar could ultimately spell its companion's demise. Pulsars in these types of binary systems are called "black widow" pulsars. Just as a black widow spider eats its mate, it is thought that the pulsar, given the right conditions, could gradually erode gas from the dwarf star until the latter is consumed.

In addition to being an observation of incredibly high resolution, the result could be a clue to the nature of mysterious phenomena known as Fast Radio Bursts, or FRBs.

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Accretion-powered pulsar reveals unique timing glitch

Composite image of the X-ray pulsar SXP 1062 surrounded by the supernova remnant. The false-color image combines X-ray (blue) and optical data (oxygen: green, hydrogen: red).

The discovery of the largest timing irregularity yet observed in a pulsar is the first confirmation that pulsars in binary systems exhibit the strange phenomenon known as a 'glitch'. The study is published in the journal Monthly Notices of the Royal Astronomical Society.

Pulsars are one possible result of the final stages of evolution of massive stars. Such stars end their lives in huge supernova explosions, ejecting their stellar materials outwards into space and leaving behind an extremely dense and compact object; this could either be a white dwarf, a neutron star or a black hole.

If a neutron star is left, it may have a very strong magnetic field and rotate extremely quickly, emitting a beam of light that can be observed when the beam points towards Earth, in much the same way as a lighthouse beam sweeping past an observer. To the observer on Earth, it looks as though the star is emitting pulses of light, hence the name 'pulsar'.

Now a group of scientists from the Middle East Technical University and Baskent University in Turkey have discovered a sudden change in the rotation speed of the peculiar pulsar SXP 1062. These jumps in frequency, known as 'glitches', are commonly seen in isolated pulsars, but have so far never been observed in binary pulsars (pulsars orbiting with a companion white dwarf or neutron star) such as SXP 1062.

SXP 1062 is located in the Small Magellanic Cloud, a satellite galaxy of our own Milky Way galaxy, and one of our nearest intergalactic neighbours at 200,000 light years away. Lead author of the study, Mr M. Mirac Serim, a senior PhD student working under the supervision of Prof Altan Baykal, said, "This pulsar is particularly interesting, since as well as orbiting its partner star as part of a binary pair, it is also still surrounded by the remnants of the supernova explosion which created it."

The pulsar is thought to pull in the leftover material from the supernova explosion, feeding on it in a process known as accretion. The team believe that the size of the glitch is due to the gravitational influence of its companion star and this accretion of the surrounding remnant material, which together exert large forces on the crust of the neutron star. When these forces are no longer sustainable, a rapid change in internal structure transfers momentum to the crust, changing the rotation of the pulsar very suddenly and producing a glitch.

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