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This Record-Breaking ‘Black Widow’ Pulsar Is The Most Massive Neutron Star Yet

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One of the most extreme stars in the Milky Way just got even more wack.

Scientists have measured the mass of a neutron star named PSR J0952-0607, and found that it’s the most massive neutron star discovered yet, clocking in at a whopping 2.35 times the mass of the Sun.

 

If true, this is very close to the theorized upper mass limit of around 2.3 solar masses for neutron stars, representing an excellent laboratory for studying these ultra-dense stars at what we think is the brink of collapse, in the hope of better understanding the weird quantum state of the matter of which they are made.

“We know roughly how matter behaves at nuclear densities, like in the nucleus of a uranium atom,” said astrophysicist Alex Filippenko of the University of California, Berkeley.

“A neutron star is like one giant nucleus, but when you have one-and-a-half solar masses of this stuff, which is about 500,000 Earth masses of nuclei all clinging together, it’s not at all clear how they will behave.”

Neutron stars are the collapsed cores of massive stars that were between around 8 and 30 times the mass of the Sun, before they went supernova and blew most of their mass off into space.

These cores, tending to be around 1.5 times the mass of the Sun, are among the densest objects in the Universe; the only thing denser is a black hole.

 

Their mass is packed into a sphere just 20 kilometers (12 miles) or so across; at that density, protons and electrons can combine into neutrons. The only thing keeping this ball of neutrons from collapsing into a black hole is the force it would take for them to occupy the same quantum states, described as degeneracy pressure.

In some ways this means neutron stars behave like massive atomic nuclei. But what happens at this tipping point, where neutrons form exotic structures or blur into a soup of smaller particles, is hard to say.

PSR J0952-0607 was already one of the most interesting neutron stars in the Milky Way. It’s what is known as a pulsar – a neutron star that is spinning very fast, with jets of radiation emitting from the poles. As the star spins, these poles sweep past the observer (us) in the manner of a cosmic lighthouse so that the star appears to pulse.

These stars can be insanely fast, their rotation rate on millisecond scales. PSR J0952-0607 is the second-fastest pulsar in the Milky Way, rotating a mind-blowing 707 times per second. (The fastest is only slightly faster, with a rotation rate of 716 times per second.)

 

It’s also what is known as a “black widow” pulsar. The star is in a close orbit with a binary companion – so close that its immense gravitational field pulls material from the companion star. This material forms an accretion disk that whirls around and feeds into the neutron star, a bit like water swirling around a drain. Angular momentum from the accretion disk is transferred to the star, causing its spin rate to increase.

A team led by astrophysicist Roger Romani of Stanford University wanted to understand better how PSR J0952-0607 fit into the timeline of this process. The binary companion star is tiny, less than 10 percent of the mass of the Sun. The research team made careful studies of the system and its orbit and used that information to obtain a new, precise measurement for the pulsar.

Their calculations returned a result of 2.35 times the mass of the Sun, give or take 0.17 solar masses. Assuming a standard neutron star starting mass of around 1.4 times the mass of the Sun, that means that PSR J0952-0607 has slurped up to an entire Sun’s worth of matter from its binary companion. This, the team says, is really important information to have about neutron stars.

“This provides some of the strongest constraints on the property of matter at several times the density seen in atomic nuclei. Indeed, many otherwise popular models of dense-matter physics are excluded by this result,” Romani explained.

“A high maximum mass for neutron stars suggests that it is a mixture of nuclei and their dissolved up and down quarks all the way to the core. This excludes many proposed states of matter, especially those with exotic interior composition.”

The binary also shows a mechanism whereby isolated pulsars, without binary companions, can have millisecond rotation rates. J0952-0607’s companion is almost gone; once it’s entirely devoured, the pulsar (if it’s not tipped over the upper mass limit and collapses further into a black hole) will retain its insanely fast rotation speed for quite some time.

And it will be alone, just like those all the other isolated millisecond pulsars. 

“As the companion star evolves and starts becoming a red giant, material spills over to the neutron star, and that spins up the neutron star. By spinning up, it now becomes incredibly energized, and a wind of particles starts coming out from the neutron star. That wind then hits the donor star and starts stripping material off, and over time, the donor star’s mass decreases to that of a planet, and if even more time passes, it disappears altogether,” Filippenko said.

“So, that’s how lone millisecond pulsars could be formed. They weren’t all alone to begin with – they had to be in a binary pair – but they gradually evaporated away their companions, and now they’re solitary.”

The research has been published in The Astrophysical Journal Letters.

 

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Astronomers Have Spotted a Record-Breaking Magnetic Field in Space, And It’s Epic

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Far out in the Milky Way, roughly 22,000 light years from Earth, a star unlike any other roars with a magnetic force that beats anything physicists have ever seen. 

At a whopping 1.6 billion Tesla, a pulsar called Swift J0243.6+6124 smashes the previous records of around 1 billion Tesla, discovered surrounding the pulsars GRO J1008-57 and 1A 0535+262.

 

For a bit of context, your average novelty fridge magnet comes in at around 0.001 Tesla. The more powerful MRI machines manage to hit around 3 Tesla.

A few years ago, engineers earned a pat on the back for achieving a semi-respectable 1,200 Tesla, sustaining it for a blink of just 100 microseconds.

So it stands to reason that 1.6 billion Tesla is going to demand some truly mind-blowing physics. The kind only achievable by massive objects crammed into impossible volumes and spun at incredible speeds, fast enough to accelerate electrons to ridiculous velocities.

Swift J0243.6+6124 was already regarded as a star worth paying attention to. A type of super-compact cosmic heavyweight known as a pulsar, it’s the only X-ray source in our galaxy to fall into the ultra-luminous category.

It’s also the only example in the Milky Way of an X-ray pulsar with a Be-type companion star feeding it matter fast enough to generate radio-emitting jets of matter from its poles.

Those features alone add up to a unique opportunity in our galactic backyard astronomers can’t help but study in detail.

 

Measuring the magnetic field of a far-distant object is easier said than done, though. As strong as they are, those fields quickly weaken to become undetectable over distances of thousands of light years.

Fortunately clues can be found in the way that the ultra-bright glow of X-rays scatters from the electrons whizzing down the magnetic racetrack, something known as a cyclotron resonance scattering feature.

China’s launch of the X-ray observatory Insight-HXMT in 2017 provides astrophysicists with a way to capture signatures like these in distant emissions, leading to the measure of electron energies in the GRO J1008-57 field in 2020.

Fortunately, an outburst of activity in Swift J0243.6+6124 following Insight-HXMT’s launch also provided a glimpse into its own high-strength magnetic field, with a cyclotron resonance scattering feature buried within its X-ray spectrum.

Researchers from the Chinese Academy of Sciences and Sun Yat-Sen University in China, and the University of Tübingen in Germany, subsequently analyzed the feature to calculate the energy of its electrons to peak at an astonishing 146 kiloelectron volts, blitzing the 90 and 100 kiloelectron volts of the previous record holders.

 

Given Swift J0243.6+6124 is the only ultra-luminescent X-ray pulsar in our galaxy, having a precise measure on its magnetic field gives astronomers a better idea of what might be happening close to its surface.

As a type of neutron star, pulsars like Swift J0243.6+6124 are made of atoms squished into configurations far beyond anything we can create on Earth. Its magnetic properties help exclude or support various models that explain how its highly compact crust behaves.

Specifically, the nature of the neutron star’s magnetism confirms the likelihood that its field is complex, consisting of multiple poles.

That’s a solid win for astrophysicists keen to understand the mysteries of some of the most exotic objects in space.

For the rest of us, it’s enough just to try to imagine the might of a 1.6 billion Tesla magnet stuck to our fridge.

This research was published in The Astrophysical Journal Letters.

 

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Astronomers Discover Evidence for Most Powerful Pulsar in Distant Galaxy

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As the shell of explosion debris from the supernova expands over a few decades, it becomes less dense and eventually becomes thin enough that radio waves from inside can escape. This allowed observations by the VLA Sky Survey to detect bright radio emission created as the rapidly spinning neutron star’s powerful magnetic field sweeps through the surrounding space, accelerating charged particles. This phenomenon is called a pulsar wind nebula. Credit: Melissa Weiss, NRAO/AUI/NSF

Astronomers analyzing data from the VLA Sky Survey (VLASS) have discovered one of the youngest known neutron stars — the superdense remnant of a massive star that exploded as a supernova. Images from the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) indicate that bright radio emission powered by the spinning

Top Left: A giant blue star, much more massive than our Sun, has consumed, through nuclear fusion at its center, all its hydrogen, helium, and heavier elements up to iron. It now has a small iron core (red dot) at its center. Unlike the earlier stages of fusion, the fusion of iron atoms absorbs, rather than releases, energy. The fusion-released energy that has held up the star against its own weight now is gone, and the star will quickly collapse, triggering a supernova explosion. Top Right: The collapse has begun, producing a superdense neutron star with a strong magnetic field at its center (inset). The neutron star, though containing about 1.5 times the mass of the Sun, is only about the size of Manhattan. Bottom Left: The supernova explosion has ejected a fast-moving shell of debris outward into interstellar space. At this stage, the debris shell is dense enough to shroud from view any radio waves coming from the region of the neutron star. Bottom Right: As the shell of explosion debris expands over a few decades, it becomes less dense and eventually becomes thin enough that radio waves from inside can escape. This allowed observations by the VLA Sky Survey to detect bright radio emission created as the rapidly spinning neutron star’s powerful magnetic field sweeps through the surrounding space, accelerating charged particles. This phenomenon is called a pulsar wind nebula. Credit: Melissa Weiss, NRAO/AUI/NSF

“What we’re most likely seeing is a pulsar wind nebula,” said Dillon Dong, a Caltech graduate student who will begin a Jansky Postdoctoral Fellowship at the National Radio Astronomy Observatory (NRAO) later this year. A pulsar wind nebula is created when the powerful magnetic field of a rapidly spinning

The scientists reported their findings at the American Astronomical Society’s meeting in Pasadena, California.

A giant blue star, much more massive than our Sun, has consumed, through nuclear fusion at its center, all its hydrogen, helium, and heavier elements up to iron. It now has a small iron core (red dot) at its center. Unlike the earlier stages of fusion, the fusion of iron atoms absorbs, rather than releases, energy. The fusion-released energy that has held up the star against its own weight now is gone, and the star will quickly collapse, triggering a supernova explosion. Credit: Melissa Weiss, NRAO/AUI/NSF

Dong and Hallinan discovered the object in data from VLASS, an NRAO project that began in 2017 to survey the entire sky visible from the VLA — about 80 percent of the sky. Over a period of seven years, VLASS is conducting a complete scan of the sky three times, with one of the objectives to find transient objects. The astronomers found VT 1137-0337 in the first VLASS scan from 2018.

Comparing that VLASS scan to data from an earlier VLA sky survey called FIRST revealed 20 particularly luminous transient objects that could be associated with known galaxies.

“This one stood out because its galaxy is experiencing a burst of star formation, and also because of the characteristics of its radio emission,” Dong said. The galaxy, called SDSS J113706.18-033737.1, is a dwarf galaxy containing about 100 million times the mass of the Sun.

The star’s collapse has begun, producing a superdense neutron star with a strong magnetic field at its center (inset). The neutron star, though containing about 1.5 times the mass of the Sun, is only about the size of Manhattan. Credit: Melissa Weiss, NRAO/AUI/NSF

In studying the characteristics of VT 1137-0337, the astronomers considered several possible explanations, including a supernova, gamma ray burst, or tidal disruption event in which a star is shredded by a supermassive

Initially, the radio emission was blocked from view by the shell of explosion debris. As that shell expanded, it became progressively less dense until eventually the radio waves from the pulsar wind nebula could pass through.

The supernova explosion has ejected a fast-moving shell of debris outward into interstellar space. At this stage, the debris shell is dense enough to shroud from view any radio waves coming from the region of the neutron star. Credit: Melissa Weiss, NRAO/AUI/NSF

“This happened between the FIRST observation in 1998 and the VLASS observation in 2018,” Hallinan said.

Probably the most famous example of a pulsar wind nebula is the Crab Nebula in the constellation Taurus, the result of a supernova that shone brightly in the year 1054. The Crab is readily visible today in small telescopes.

“The object we have found appears to be approximately 10,000 times more energetic than the Crab, with a stronger magnetic field,” Dong said. “It likely is an emerging ‘super Crab’,” he added.

VLA images of the location of VT 1137-0337 in 1998, left, and 2018, right. The object became visible to the VLA sometime between these two dates. Credit: Dong & Hallinan, NRAO/AUI/NSF

While Dong and Hallinan consider VT 1137-0337 to most likely be a pulsar wind nebula, it also is possible that its magnetic field may be strong enough for the neutron star to qualify as a magnetar — a class of super-magnetic objects. Magnetars are a leading candidate for the origin of the mysterious Fast Radio Bursts (FRBs) now under intense study.

“In that case, this would be the first magnetar caught in the act of appearing, and that, too, is extremely exciting,” Dong said.

Indeed some Fast Radio Bursts have been found to be associated with persistent radio sources, the nature of which also is a mystery. They bear a strong resemblance in their properties to VT 1137-0337, but have shown no evidence of strong variability.

“Our discovery of a very similar source switching on suggests that the radio sources associated with FRBs also may be luminous pulsar wind nebulae,” Dong said.

The astronomers plan to conduct further observations to learn more about the object and to monitor its behavior over time.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.



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NASA’s Chandra Catches Pulsar in X-Ray Speed Trap

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The G292.0+1.8 supernova remnant contains a pulsar moving at over a million miles per hour, as seen in the Chandra image along with an optical image from the Digitized Sky Survey. Pulsars are rapidly spinning neutron stars that can form when massive stars run out of fuel, collapse, and explode. Sometimes these explosions produce a “kick,” which sent this pulsar racing through the remains of the supernova explosion. Additional images show a close-up look at this pulsar in X-rays from Chandra, which observed it both in 2006 and 2016 to measure this remarkable speed. The red crosses in each panel show the position of the pulsar in 2006. Credit: X-ray: NASA/CXC/SAO/L. Xi et al.; Optical: Palomar DSS2

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    The G292.0+1.8 supernova remnant contains a pulsar moving at over a million miles per hour. This image features data from NASA’s Chandra X-ray Observatory (red, orange, yellow, and blue), which was used to make this discovery. The X-rays were combined with an optical image from the Digitized Sky Survey, a ground-based survey of the entire sky.

    Pulsars are rapidly spinning neutron stars that can form when massive stars run out of fuel, collapse and explode. Sometimes these explosions produce a “kick,” which is what sent this pulsar racing through the remains of the supernova explosion. An inset shows a close-up look at this pulsar in X-rays from Chandra.

    To make this discovery, the researchers compared Chandra images of G292.0+1.8 taken in 2006 and 2016. A pair of supplemental images show the change in position of the pulsar over the 10-year span. The shift in the source’s position is small because the pulsar is about 20,000 light-years from Earth, but it traveled about 120 billion miles (190 billion km) over this period. The researchers were able to measure this by combining Chandra’s high-resolution images with a careful technique of checking the coordinates of the pulsar and other X-ray sources by using precise positions from the Gaia satellite.

    Pulsar Positions, 2006 & 2016. Credit: X-ray: NASA/CXC/SAO/L. Xi et al.

    The team calculated the pulsar is moving at least 1.4 million miles per hour from the center of the supernova remnant to the lower left. This speed is about 30% higher than a previous estimate of the pulsar’s speed that was based on an indirect method, by measuring how far the pulsar is from the center of the explosion.

    The newly determined speed of the pulsar indicates that G292.0+1.8 and its pulsar may be significantly younger than astronomers previously thought. The researchers estimate that G292.0+1.8 would have exploded about 2,000 years ago as seen from Earth, rather than 3,000 years ago as previously calculated. This new estimate of the age of G292.0+1.8 is based on extrapolating the position of the pulsar backward in time so that it coincides with the center of the explosion.

    Several civilizations around the globe were recording supernova explosions at that time, opening the possibility that G292.0+1.8 was directly observed. However, G292.0+1.8 is below the horizon for most northern hemisphere civilizations that might have observed it, and there are no recorded examples of a supernova being observed in the southern hemisphere in the direction of G292.0+1.8.

    A close-up view of the center of the Chandra image of G292+1.8. The direction of motion of the pulsar is shown (arrow), and the position of the center of the explosion (green oval) based on the motion of debris seen in optical data. The position of the pulsar is extrapolated back 3,000 years and the triangle depicts the uncertainty in the angle of the extrapolation. Agreement of the extrapolated position with the center of the explosion gives an age of about 2,000 years for the pulsar and G292+1.8. The center of mass (cross) of X-ray-detected elements in the debris (Si, S, Ar, Ca) is on the opposite side of the center of the explosion from the moving pulsar. This asymmetry in the debris to the upper right of the explosion resulted in the pulsar being kicked to the lower left, by conservation of momentum. Credit: X-ray: NASA/CXC/SAO/L. Xi et al.; Optical: Palomar DSS2

    In addition to learning more about the age of G292.0+1.8, the research team also examined how the supernova gave the pulsar its powerful kick. There are two main possibilities, both involving material not being ejected by the supernova evenly in all directions. One possibility is that neutrinos produced in the explosion are ejected from the explosion asymmetrically, and the other is that the debris from the explosion is ejected asymmetrically. If the material has a preferred direction the pulsar will be kicked in the opposite direction because of the principle of physics called the conservation of momentum.

    The amount of asymmetry of neutrinos required to explain the high speed in this latest result would be extreme, supporting the explanation that asymmetry in the explosion debris gave the pulsar its kick.

    The energy imparted to the pulsar from this explosion was gigantic. Although only about 10 miles across, the pulsar’s mass is 500,000 times that of the Earth and it is traveling 20 times faster than Earth’s speed orbiting the Sun.

    The latest work by Xi Long and Paul Plucinksky (Center for Astrophysics | Harvard & Smithsonian) on G292.0+1.8 was presented at the 240th meeting of the American Astronomical Society meeting in Pasadena, CA. The results are also discussed in a paper that has been accepted for publication in The Astrophysical Journal. The other authors of the paper are Daniel Patnaude and Terrance Gaetz, both from the Center for Astrophysics.

    Reference: “The Proper Motion of the Pulsar J1124-5916 in the Galactic Supernova Remnant G292.0+1.8” by Xi Long, Daniel J. Patnaude, Paul P. Plucinsky and Terrance J. Gaetz, Accepted, The Astrophysical Journal.
    arXiv:2205.07951

    NASA’s Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.



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At 1.4 Million Mph, Astronomers Detected One of The Fastest Cosmic Objects of Its Kind

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When massive stars die, they don’t do so quietly.

Their deaths are spectacularly brilliant affairs that light up the cosmos, a supernova explosion that sends star guts punching out into space in a cloud of splendor. Meanwhile, the core of the star-that-was can linger on, collapsed into an ultra-dense neutron star or black hole.

 

If that explosion takes place in a certain way, it can send the collapsed core barreling across the Milky Way like a bat out of hell, at such insane velocities they can eventually punch clean out of the galaxy altogether, on a wild journey into intergalactic space.

It’s one of these objects that has been newly measured via data from the Chandra X-ray observatory: a type of pulsing neutron star known as a pulsar, ripping through its own entrails at a speed of around 612 kilometers per second (or 1.4 million miles per hour).

It’s one of the fastest objects of this kind ever detected. (The fastest known star in the Milky Way is not a supernova remnant that has been kicked by an explosion, but a star orbiting Sgr A*, the supermassive black hole in the galactic center. At the fastest point in its orbit, it moves at a wild 24,000 kilometers per second.)

“We directly saw motion of the pulsar in X-rays, something we could only do with Chandra’s very sharp vision,” said astrophysicist Xi Long of the Harvard & Smithsonian Center for Astrophysics (CfA).

 

“Because it is so distant, we had to measure the equivalent of the width of a quarter about 15 miles away to see this motion.”

The detection was made by looking at a glowing supernova remnant some 20,000 light-years away, named G292.0+1.8. Previous observations had revealed a speeding pulsar therein. Long and his colleagues wanted to study the object to see if it could reveal the history of the supernova, by tracing its motion to the center of the object in reverse.

“We only have a handful of supernova explosions that also have a reliable historical record tied to them,” said astrophysicist Daniel Patnaude of the CfA, “so we wanted to check if G292.0+1.8 could be added to this group.”

They studied images taken of the supernova remnant in 2006 and 2016, and used Gaia data on its current location in the Milky Way, comparing the differences in the pulsar’s position. These comparisons revealed something extremely interesting: The dead star appears to be moving 30 percent faster than previous estimates had suggested.

This means it has taken a much shorter time to travel from the center of the supernova remnant, suggesting the supernova itself took place much more recently. Previous estimates put the date of the supernova at around 3,000 years ago; the new estimates take it to around 2,000 years ago.

 

The revised velocity of the pulsar also allowed the team to conduct a new, detailed investigation into how the dead star might have been ejected from the center of the supernova. They came up with two scenarios, both involving a similar mechanism.

In the first, neutrinos are ejected from the supernova explosion asymmetrically. In the other, debris from the explosion is ejected asymmetrically. However, because the neutrino energy would need to be extremely large, the more likely explanation is asymmetrical debris.

Basically, a lopsided explosion can ‘kick’ the collapsed core of a dead star out into space at extremely high speeds; in this case, the star is currently traveling at a speed higher than the Milky Way mid-disk escape velocity of 550 kilometers per second, although it will take quite some time to get there, and it may slow down over time.

In fact, its true speed may be even higher than 612 kilometers per second, because it is traveling very slightly along our line of sight.

“This pulsar is about 200 million times more energetic than Earth’s motion around the Sun,” said astrophysicist Paul Plucinsky of CfA. “It appears to have received its powerful kick just because the supernova explosion was asymmetric.”

The team’s research, presented at the 240th meeting of the American Astronomical Society, has been accepted into The Astrophysical Journal and is available on arXiv.

 

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An Ultra-Rare Cosmic Object Was Just Detected in The Milky Way, Astronomers Report

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A new member of a category of star so rare we can count the known number of them on our fingers and toes has just been discovered in the Milky Way.

It’s called MAXI J1816-195, located no greater than 30,000 light-years away. Preliminary observations and investigations suggest that it’s an accreting X-ray millisecond pulsar – of which only 18 others are known, according to a pulsar database compiled by astronomer Alessandro Patruno.

 

When numbers are that low, any new object represents an extremely exciting find that can yield important statistical information about how those objects form, evolve, and behave.

The discovery really is hot off the presses. X-ray light emanating from the object was first detected on 7 June by the Japanese Space Agency’s Monitor of All-sky X-ray Image (MAXI) instrument mounted on the outside of the ISS.

In a notice posted to The Astronomer’s Telegram (ATel), a team headed by astrophysicist Hitoshi Negoro of Nihon University in Japan posted that they’d identified a previously uncatalogued X-ray source, located in the galactic plane between the constellations of Sagittarius, Scutum, and Serpens. It was, they said, flaring relatively brightly, but they hadn’t been able to identify it based on the MAXI data.

It wasn’t long before other astronomers piled on. Using the Neil Gehrels Swift Observatory, a space-based telescope, astrophysicist Jamie Kennea of Pennsylvania State University and colleagues homed in on the location to confirm the detection with an independent instrument, and localize it.

Swift saw the object in X-rays, but not optical or ultraviolet light, at the location specified by the MAXI observations.

 

“This location does not lie at the location of any known catalogued X-ray source, therefore we agree that this is a new transient source MAXI J1816-195,” they wrote in a notice posted to ATel.

“In addition, archival observations by Swift/XRT of this region taken in 2017 June 22, do not reveal any point source at this location.”

Curiouser and curiouser.

Next up was the Neutron Star Interior Composition Explorer (NICER), an X-ray NASA instrument also mounted to the ISS, in an investigation led by astrophysicist Peter Bult of NASA’s Goddard Space Flight Center.

And this is where things started to get really interesting. NICER picked up X-ray pulsations at 528.6 Hz – suggesting that the thing is spinning at a rate of 528.6 times per second – in addition to an X-ray thermonuclear burst.

“This detection,” they wrote, “shows that MAXI J1816-195 is a neutron star and a new accreting millisecond X-ray pulsar.”

So what does that mean? Well, not all pulsars are built alike. At the very basic level, a pulsar is a type of neutron star, which is the collapsed core of a dead massive star that has gone supernova. These objects are very small and very dense – up to around 2.2 times the mass of the Sun, packed into a sphere just 20 kilometers (12 miles) or so across.

 

To be classified as a pulsar, a neutron star has to… pulse. Beams of radiation are launched from its poles; because of the way the star is angled, these beams sweep past Earth like the beams from a lighthouse. Millisecond pulsars are pulsars that spin so fast, they pulse hundreds of times a second.

Some pulsars are powered purely by rotation, but another type is powered by accretion. The neutron star is in a binary system with another star, their orbit so close that material is siphoned from the companion star and onto the neutron star. This material is channeled along the neutron star’s magnetic field lines to its poles, where it falls down onto the surface, producing hotspots that flare brightly in X-rays.

In some cases, the accretion process can spin up the pulsar to millisecond rotational speeds. This is the accreting X-ray millisecond pulsar, and it appears that MAXI J1816-195 belongs to this rare category.

The thermonuclear X-ray burst detected by NICER was likely the result of the unstable thermonuclear burning of material accumulated by the companion star.

Since the discovery is so new, observations in multiple wavelengths are ongoing. Follow-up has already been conducted using Swift, and the 2m Liverpool Telescope on the Canary Island of La Palma in Spain was employed to look for an optical counterpart, although none was detected. Other astronomers are also encouraged to climb aboard the MAXI J1816-195 train.

Meanwhile, a full pulsar timing analysis is being conducted, and will, Bult and his team said, be circulated as more data becomes available. You can follow along on ATel.

 

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A ‘galaxy’ is unmasked as a pulsar — the brightest outside the Milky Way

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The brightest extra-galactic pulsar has been identified in the Large Magellanic Cloud (pictured).Credit: Pennock et al.

Astronomers have confirmed that an object they thought was a distant galaxy is actually the brightest extra-galactic pulsar ever seen. The team made the discovery using a technique that blocks a particular type of polarized light, similar to polarized sunglasses, which could be used to spy more ‘hidden’ pulsars.

Pulsars are highly magnetized spinning neutron stars that form from the collapsed remnants of exploded stars. As pulsars spin, they release a stream of radio waves from their poles — a ‘pulse’ that can be detected using radio telescopes. Astronomers use pulsars to test theories of gravity and to look for evidence of gravitational waves.

The new pulsar, called PSR J0523−7125, is about 50,000 parsecs from Earth, in the Large Magellanic Cloud (LMC), and is quite different from most known pulsars. Its pulse is very wide — more than twice the size of other known pulsars in the LMC, and it is exceptionally ‘bright’ on the radio spectrum, says Yuanming Wang, an astrophysicist at Australia’s Commonwealth Scientific and Industrial Research Organisation in Canberra.

Wang and the team say the pulsar is ten times brighter than any other pulsar found outside the Milky Way. Their study is published in The Astrophysical Journal today1.

“Because of its unusual properties, this pulsar was missed by previous studies, despite how bright it is,” said co-author, Tara Murphy, a radio astronomer at the University of Sydney in Australia, in a press release.

New technique

Pulsars are typically identified from their faint pulse, flickering periodically. But in the case of PSR J0523−7125, its pulse is so wide and bright, that it didn’t fit the typical profile of a pulsar and was dismissed as a galaxy.

Wang and an international team of astronomers first suspected the object might be a pulsar in data from the Variables and Slow Transients survey, conducted using the Australian Square Kilometre Array Pathfinder (ASKAP) telescope in Western Australia. The survey looks at a large amount of sky for highly variable radio wave sources, and collects circular polarization, among other data.

Emissions from pulsars are often highly polarized, and some of them oscillate in a circular way. Few space objects are polarized like this, which makes them stand out.

Using a computer programme, the team was able to block out wavelengths of light that were not circularly polarized, revealing the rare type of pulsar. Other telescopes, including the MeerKAT radio-astronomy telescope in South Africa, confirmed their finding (see Hidden pulsar).

“We should expect to find more pulsars using this technique. This is the first time we have been able to search for a pulsar’s polarization in a systematic and routine way,” said Murphy.

Yvette Cendes, a radio astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, says that radio astronomy hasn’t been as effective as optical astronomy at finding ‘transient’ objects — space objects like pulsars that come in and out of view. “Surveys like VAST are changing that,” she says.

“But just because you find a transient [object] doesn’t mean it’s easy to figure out what it is,” she says. Polarization data helped to narrow down the source of the object, which suggests the technique has the potential to identify other transients in the future, she says.

Although other telescopes are collecting polarization data, there have only been a few large-scale radio surveys using the circular polarization technique. In March, researchers using data from the Low-Frequency Array (LOFAR) telescope in the Netherlands found two new pulsars using the technique, which they detailed in a preprint posted on arXiv2.

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Something’s Glowing at The Galactic Core, And We Could Be Closer to Solving The Mystery

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Something deep in the heart of the Milky Way galaxy is glowing with gamma radiation, and nobody can figure out for sure what it might be.

Colliding dark matter has been proposed, ruled out, and then tentatively reconsidered.

 

Dense, rapidly rotating objects called pulsars were also considered as candidate sources of the high-energy rays, before being dismissed as too few in number to make the sums work.

A study by researchers from Australia, New Zealand and Japan could breathe new life into the pulsar explanation, revealing how it might be possible to squeeze some serious intense sunshine from a population of spinning stars without breaking any rules.

Gamma radiation isn’t your typical hue of sunlight. It requires some of the Universe’s most energetic processes to produce. We’re talking black holes colliding, matter being whipped towards light speed, antimatter combining with matter kinds of processes.

Of course, the center of the Milky Way has all of these things in spades. So when we gaze into the heavens and consider all of the crashing bits of matter, spiraling black holes, whizzing pulsars, and other astrophysical processes, we’d expect to see a healthy gamma glow.

But when researchers used NASA’s Fermi telescope to measure the intense shine within the heart of our galaxy about ten years ago, they found there was more of this high-energy light than they could account for: what’s known as the Galactic Centre Excess.

 

One exciting possibility involves unseen bits of matter bumping together in the night. These weakly interacting massive particles – a hypothetical category of dark matter commonly described as WIMPs – would cancel each other out as they smoosh together, leaving nothing but radiation to mark their presence.

It’s a fun explanation to consider, but is also light on evidence.

“The nature of dark matter is entirely unknown, so any potential clues garner a lot of excitement,” says astrophysicist Roland Crocker from the Australian National University.

“But our results point to another important source of gamma ray production.”

That source is the millisecond pulsar.

To make one, take a star much bigger than our own and let its fires die down. It will eventually collapse into a dense ball not much wider than a city, where its atoms pack together so tightly, many of its protons are slowly baked into neutrons.

This process generates super-strong magnetic fields that channel incoming particles into fast-flowing streams glowing with radiation.

Since the object is rotating, these streams swivel around from the star’s poles like the Universe’s biggest lighthouse beacons – so it appears to pulse with energy. Pulsing stars that spin hundreds of times a second are known as millisecond pulsars, and we know a lot about the conditions under which they’re likely to form.

 

“Scientists have previously detected gamma-ray emissions from individual millisecond pulsars in the neighborhood of the Solar System, so we know these objects emit gamma rays,” says Crocker.

To emit them, however, they’d need a generous amount of mass to feed on. Most pulsar systems in the center of the Milky Way are thought to be too puny to emit anything more energetic than X-rays, though.

That might not always be the case, however, especially if the dead stars they emerged from are of a particular variety of ultra-massive white dwarf.

According to Crocker, if enough of these heavyweights were to turn into pulsars and hold onto their binary partners, they would provide just the right amount of gamma radiation to match observations.

“Our model demonstrates that the integrated emission from a whole population of such stars, around 100,000 in number, would produce a signal entirely compatible with the Galactic Centre Excess,” says Crocker.

Being a purely theoretical model, it’s an idea that now needs a generous dose of empirical evidence. Unlike suggestions based on dark matter, however, we already know exactly what to look for.

This research was published in Nature Astronomy.  

 

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Mysterious Signal Coming From Our Galaxy Could Be One of The Rarest Known Objects

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A mysterious, repeating radio signal in the Milky Way that baffled astronomers could be an object so rare, only one other has ever been tentatively identified.

According to a paper by astrophysicist Jonathan Katz of Washington University at St. Louis, uploaded to preprint server arXiv, and yet to be peer-reviewed, the signal named GLEAM-X J162759.5−523504.3 could be a white dwarf radio pulsar.

 

“Since the early days of pulsar astronomy there has been speculation that a rotating magnetic white dwarf might show pulsar-like activity,” Katz wrote in his paper.

“The recently discovered periodic radio transient GLEAM-X J162759.5−523504.3 is a candidate for the first true white dwarf pulsar. It has a period of 18.18 minutes (1091 s) and its pulses show low frequency (72–215 MHz) emission with a brightness temperature ∼ 1016 K implying coherent emission. It has no binary companion with which to interact. It thus meets the criteria of a classical pulsar, although its period is hundreds of times longer than any of theirs.”

When a star dies, there are a range of outcomes, once it has ejected its outer material and core, no longer supported by the outward pressure of fusion, it collapses under its own gravity.

If the precursor star is over around 30 times the mass of the Sun, the core collapses into a black hole.

A precursor star between eight and 30 times the mass of the Sun results in a neutron star, around 20 kilometers (12 miles) across and up to around 1.4 times the mass of the Sun.

 

The core of a precursor star less than eight times the mass of the Sun will collapse into a white dwarf, packing mass up to 1.5 times that of the Sun into a ball between the sizes of Earth and the Moon.

Pulsars are a subset of neutron stars. They’re neutron stars that rotate insanely fast, and angled in such a way that beams of bright radio waves shooting from the magnetic poles sweep past Earth on every rotation – on the scale of seconds down to milliseconds. (Here’s what that sounds like transcribed into audio.)

Scientists have wondered if similar behavior might be observed in white dwarf stars, and in 2016, they seem to have come close, with a star called AR Scorpii. Locked in a binary system with a red dwarf star, AR Scorpii flashes on a timescale of minutes.

However, as Katz notes, its binary orbit is closer than those of neutron star pulsars in binary systems, and the periodic signal lacks coherence. This means that the physical processes that produces the signal might be very different from traditional radio pulsars. 

 

This brings us back to GLEAM-X J162759.5−523504.3, located roughly 4,000 light-years away from Earth. From January to March of 2018, data collected by the Murchison Widefield Array in the Australian desert showed it  pulsing brightly for roughly 30 to 60 seconds, every 18.18 minutes – one of the most luminous objects in the low-frequency radio sky.

It matched the profile of no known astronomical object, but the research team that discovered it thought it might be a hypothetical object known as an ultra-long-period magnetar. That’s a neutron star with an extraordinarily powerful magnetic field, but the explanation still didn’t quite fit.

“Nobody expected to directly detect one like this because we didn’t expect them to be so bright,” astrophysicist Natasha Hurley-Walker of the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) in Australia explained at the time. “Somehow it’s converting magnetic energy to radio waves much more effectively than anything we’ve seen before.”

A pulsar was considered as a possibility, but there are two major problems: the first is that long rotation period, and the second is that the pulses were too bright for a neutron star pulsar. Both these problems, Katz lays out, are resolved if the object is a white dwarf.

If this is the case, it would be the first white dwarf discovered that shares the physics and radiation mechanism of traditional radio pulsars. This means that GLEAM-X J162759.5−523504.3 could be a promising target for optical observations; although white dwarfs are very dim, and we might not be able to pick up any visible light at its distance. Nevertheless, given the possibility, it’s worth a shot.

And astronomers could also examine other white dwarfs, to see if they match any of the properties of GLEAM-X J162759.5−523504.3.

“If it were bright enough, optical observations could also determine its magnetic field, spectroscopically or polarimetrically,” Katz explained.

“The fast-rotating, strongly magnetized, white dwarves would be promising targets for low frequency radio observations to determine if any of them are white dwarf pulsars.”

The paper has been uploaded to preprint server arXiv.

 

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Radio Pulsar Binary Proves Einstein at Least 99.99% Right

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Researchers have conducted 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. Credit: Max Planck Institute for Radio Astronomy

More than a hundred years have passed since Einstein formalized his theory of General Relativity (GR), the geometric theory of gravitation that revolutionized our understanding of the Universe. And yet, astronomers are still subjecting it to rigorous tests, hoping to find deviations from this established theory. The reason is simple: any indication of physics beyond GR would open new windows onto the Universe and help resolve some of the deepest mysteries about the cosmos.

One of the most rigorous tests ever was recently conducted by an international team of astronomers led by Michael Kramer of the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany. Using seven radio telescopes from across the world, Kramer and his colleagues observed a unique pair of pulsars for 16 years. In the process, they observed effects predicted by GR for the first time, and with an

Pulsars are fast-spinning neutron stars that emit narrow, sweeping beams of radio waves. Credit: NASA’s Goddard Space Flight Center

“Radio pulsars” are a special class of rapidly rotating, highly magnetized neutron stars. These super-dense objects emit powerful radio beams from their poles that (when combined with their rapid rotation) create a strobing effect that resembles a lighthouse. Astronomers are fascinated by pulsars because they provide a wealth of information on the physics governing ultra-compact objects, magnetic fields, the interstellar medium (ISM), planetary physics, and even cosmology.

In addition, the extreme gravitational forces involved allow astronomers to test predictions made by gravitational theories like GR and Modified Newtonian Dynamics (MOND) under some of the most extreme conditions imaginable. For the sake of their study, Kramer and his team examined PSR J0737-3039 A/B, the “Double Pulsar” system located 2,400 light-years from Earth in the constellation Puppis.

This system is the only radio

“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

Artist’s impression of the path of the star S2 passing very close to Sagittarius A*, which also allows astronomers to test predictions made by General Relativity under extreme conditions. Credit: ESO/M. Kornmesser

Seven radio telescopes were used for the 16-year observation campaign, including the Parkes radio telescope (Australia), the Green Bank Telescope (US), the Nançay Radio Telescope (France), the Effelsberg 100-m telescope (Germany), the Lovell Radio Telescope (UK), the Westerbork Synthesis Radio Telescope (Netherlands), and the Very Long Baseline Array (US).

These observatories covered different parts of the radio spectrum, ranging from 334 MHz and 700 MHz to 1300 – 1700 MHz, 1484 MHz, and 2520 MHz. In so doing, they were able to see how photons coming from this binary pulsar were affected by its strong gravitational pull. As study co-author Prof. Ingrid Stairs from the University of British Columbia (UBC) at Vancouver explained:

“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.”

As co-author Prof. Dick Manchester from Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) added, the fast orbital motion of compact objects like these allowed them to test seven different predictions of GR. These include gravitational waves, light propagation (“Shapiro delay and light bending), time dilation, mass-energy equivalence (E=mc2), and what effect the electromagnetic radiation has on the pulsar’s orbital motion.

The Robert C. Byrd Green Bank Telescope (GBT) in West Virginia. Credit: GBO/AUI/NSF

“This radiation corresponds to a mass loss of 8 million tonnes per second!” he said. “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 made extremely precise measurements of changes to the pulsars’ orbital orientation, a relativistic effect that was first observed with the orbit of Mercury – and one of the mysteries Einstein’s theory of GR helped resolve.

Only here, the effect was 140,000 times stronger, which led the team to realize that they also needed to consider the impact of the pulsar’s rotation on the surrounding spacetime – aka. the Lense-Thirring effect, or “frame-dragging.” As Dr. Norbert Wex from the MPIfR, another main author of the study, this allowed for another breakthrough:

“In our experiment it means that we need to consider the internal structure of a pulsar as a

Artist’s illustration of two merging neutron stars. The narrow beams represent the gamma-ray burst, while the rippling spacetime grid indicates the isotropic gravitational waves that characterize the merger. Credit: NSF/LIGO/Sonoma State University/A. Simonnet