Astronomy

GW from merging of neutron stars and black holes

GW from merging of neutron stars and black holes

If it had been detected gravitational waves from merging of black holes (BH), and neutron stars (NS), why there are no detection of black holes merging with neutron stars?

Why a BH-NS merging should be a rarer event than BH-BH and NS-NS?


I don't think we have a clear answer yet. LIGO hoped to detect black hole (BH) mergers and expected to detect neutron star (NS) mergers, yet the BH mergers are observed more frequently, partly because they are louder and thus LIGO can see them from further away and partly because the 20-40 solar mass BHs LIGO observed are more common than we expected.

BHs this size can be formed by the supernova implosion of a massive star, but BHs formed this way should be quite rare They can also be formed by the merger of two smaller BHs -- which is exactly what LIGO was observing! It seems likely that these larger (but still stellar mass) BHs were produced by previous mergers.

So in the end, the frequency of LIGO detections depends on two things: The real distribution of objects in binaries: NS-NS, NS-BH, and BH-BH and the loudness/brightness of the gravitational waves emitted by the merger.

In general, black holes form from more massive stars than neutron stars, and that means rarer stars. (The moreso since the more massive a star is, the quicker it sheds mass through stellar winds.)

So NS-NS systems come from lesser-massive stellar pairs. NS-BH systems form the same way, but with one of the original stars being more massive than would lead to a NS. On the other hand, the BH-BH systems we're detecting probably come from BHs that themselves were the result of mergers in very dense stellar environments.

Consequently, we wouldn't expect that NS-BH mergers would be especially correlated with BH-BH mergers, since they precursor systems are formed through different mechanisms. But we would expect NS-BH mergers to be rarer than NS-NS mergers since the precursor systems are rarer.

There's a bit of handwaving in that! I'll try to find some papers on the subject -- there must be a bunch.


Astronomers Spy a Black Hole Devouring a Neutron Star

Charlie Wood is a journalist covering discoveries in the physical sciences both on and off the planet. His writing has appeared in Quanta Magazine, Popular Science, and elsewhere.
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Charlie Wood is a journalist covering discoveries in the physical sciences both on and off the planet. His writing has appeared in Quanta Magazine, Popular Science, and elsewhere.

Some 870 million years ago two dead stars became one. Their merger shook the fabric of space with a gravitational wave that swept through Earth on August 14, 2019, rippling through three pairs of carefully calibrated lasers designed to detect their passage. An automated system sent out a preliminary alert 21 seconds later, vibrating smartphones and pinging laptops around the world.

A few years after the Nobel Prize&ndashwinning first gravitational-wave detection, which stemmed from a pair of colliding black holes, such alerts had become commonplace. This time, however, astrophysicists instantly knew that the observed event was special. &ldquoMy jaw dropped when I saw the data,&rdquo says Geoffrey Lovelace of California State University, Fullerton, a member of the Laser Interferometer Gravitational-wave Observatory (LIGO) Scientific Collaboration.

The wave was detected by LIGO in the U.S. and the Virgo Observatory in Italy at 21:11:18 UTC on August 14, 2019. An automatic first pass pegged it as resulting from an unprecedented merger between a pair of bodies too light to classify, sending astronomers scrambling to look for additional electromagnetic emissions from the event. Subsequent analysis recategorized the signal as a collision between a black hole and a neutron star, a stellar remnant in which gravity squeezes an entire sun&rsquos mass into a ball the size of a city. This may be the first such event detected with confidence and, after black hole&ndashblack hole mash-ups and mergers between two neutron stars, the third variety of collision detected by gravitational waves. While the classification remains uncertain, this event, now known as GW190814, marks the beginning of a new era of astrophysical studies, with implications for how researchers understand Einstein&rsquos general theory of relativity, the deaths of stars and the behavior of extreme matter.


Why Detect Them?

Historically, scientists have relied almost exclusively on electromagnetic (EM) radiation (visible light, X-rays, radio waves, microwaves, etc.) to study the Universe. Some are trying to use subatomic particles, called neutrinos, as well. Each of these 'messengers' of information provides scientists with a different but complementary view of the Universe.

Gravitational waves, however, are completely unrelated to EM radiation. They are as distinct from light as hearing is from vision. Imagine humans were a species that only had eyes and no ears. You can learn a lot about the world around you simply by studying the light from objects. Then one day, someone invents something they call an ear. This device senses vibrations in air or water that you could not have known existed before. This ear opens up an entirely new realm of observation that you didn't have access to simply by studying electromagnetic radiation! As an antenna able to detect vibrations in the 'medium' of space-time, LIGO is akin to a human ear able to detect vibrations in a medium like air or water.

This is the way in which LIGO has opened a new 'window' on the universe. Things like colliding black holes are utterly invisible to EM astronomers. To LIGO, such events are beacons in the vast cosmic sea.

More importantly, since gravitational waves interact very weakly with matter (unlike EM radiation, which can be absorbed, reflected, refracted, or bent), they travel through the Universe virtually unimpeded, giving us a clear view of the gravitational-wave Universe. The waves carry information about their origins that is free of the distortions or alterations suffered by EM radiation as it traverses intergalactic space.

The gravitational waves that LIGO detects are caused by some of the most energetic events in the Universe&mdashcolliding black holes, merging neutron stars, exploding stars, and possibly even the birth of the Universe itself. Detecting and analyzing the information carried by gravitational waves is allowing us to observe the Universe in a way never before possible, providing astronomers and other scientists with their first glimpses of literally un-seeable wonders. LIGO has removed a veil of mystery on the Universe and in so doing, has ushered in exciting new research in physics, astronomy, and astrophysics.


Videos

Neutron star merger (Credit: Christopher W. Evans/Georgia Tech)

Jets and Debris from Neutron Star Collision (Credit: NASA/Goddard Space Flight Center/CI Lab)

Last Dance of Neutron Star Pair (Credit: W. Kastaun/T. Kawamura/B. Giacomazzo/R. Ciolfi/A. Endrizzi)

Ripples of Gravity, Flashes of Light (Credit: LIGO/Virgo)

Zooming in on the Source of Gravitational Waves (Credit: LIGO-Virgo)

Final Flight of Neutron Star Pair (Credit: LIGO-Virgo/Aaron Geller/Northwestern University)

Hearing the Wave (Credit: Alex Nitz/Max Planck Institute for Gravitational Physics/LIGO)


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Research output : Contribution to journal › Article › peer-review

T1 - Eccentric black-hole-neutron-star mergers

N2 - Within the next few years gravitational waves (GWs) from merging black holes (BHs) and neutron stars (NSs) may be directly detected, making a thorough theoretical understanding of these systems a high priority. As an additional motivation, these systems may represent a subset of short-duration gamma-ray burst progenitors. BH-NS mergers are expected to result from primordial, quasi-circular inspiral as well as dynamically formed capture binaries. The latter channel allows mergers with high eccentricity, resulting in a richer variety of outcomes. We perform general relativistic simulations of BH-NS interactions with a range of impact parameters, and find significant variation in the properties of these events that have potentially observable consequences, namely, the GW signature, remnant accretion disk mass, and amount of unbound material.

AB - Within the next few years gravitational waves (GWs) from merging black holes (BHs) and neutron stars (NSs) may be directly detected, making a thorough theoretical understanding of these systems a high priority. As an additional motivation, these systems may represent a subset of short-duration gamma-ray burst progenitors. BH-NS mergers are expected to result from primordial, quasi-circular inspiral as well as dynamically formed capture binaries. The latter channel allows mergers with high eccentricity, resulting in a richer variety of outcomes. We perform general relativistic simulations of BH-NS interactions with a range of impact parameters, and find significant variation in the properties of these events that have potentially observable consequences, namely, the GW signature, remnant accretion disk mass, and amount of unbound material.


GW Scientists Propose New Method to Refine the Hubble Constant—the Expansion and Age of the Universe (Astronomy)

A team of international scientists, led by the Galician Institute of High Energy Physics (IGFAE) and the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), has proposed a simple and novel method to bring the accuracy of the Hubble constant measurements down to 2%, using a single observation of a pair of merging neutron stars.

The Universe is in continuous expansion. Because of this, distant objects such as galaxies move away from us. In fact, the further away they are, the faster they move. Scientists describe this expansion through a famous number known as the Hubble constant, which tells us how fast objects in the Universe recede from us depending on their distance to us. By measuring the Hubble constant in a precise way, we can also determine some of the most fundamental properties of the Universe, including its age.

For decades, scientists have measured Hubble’s constant with increasing accuracy, collecting electromagnetic signals emitted throughout the Universe but arriving at a challenging result: the two current best measurements give inconsistent results. Since 2015, scientists have tried to tackle this challenge with the science of gravitational waves: ripples in the fabric of space-time that travel at the speed of light. Gravitational waves are generated in the most violent cosmic events and provide a new channel of information about the Universe. They’re emitted during the collision of two neutron stars—the dense cores of collapsed stars–and can help scientists dig deeper into the Hubble constant mystery.

Unlike black holes, merging neutron stars produce both gravitational and electromagnetic waves, such as x-rays, radio waves and visible light. While gravitational waves can measure the distance between the neutron-star merger and Earth, electromagnetic waves can measure how fast its whole galaxy is moving away from Earth. This creates a new way to measure the Hubble constant. However, even with the help of gravitational waves, it’s still tricky to measure the distance to neutron-star mergers–that’s, in part, why current gravitational-wave based measurements of the Hubble constant have an uncertainty of

16%, much larger than existing measurements using other traditional techniques.

In a recently published article in the prestigious journal The Astrophysical Journal Letters, a team of scientists led by ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) and Monash University alumni Prof Juan Calderón Bustillo (now La Caixa Junior Leader and Marie Curie Fellow at the Galician institute of High Energy Physics of the University of Santiago de Compostela, Spain), has proposed a simple and novel method to bring the accuracy of these measurements down to 2% using a single observation of a pair of merging neutron stars.

According to Prof Calderón Bustillo, it’s difficult to interpret how far away these mergers occur because ‘currently, we can’t say if the binary is very far away and facing Earth, or if it’s much closer, with the Earth in its orbital plane’. To decide between these two scenarios, the team proposed to study secondary, much weaker components of the gravitational-wave signals emitted by neutron-star mergers, known as higher modes. ‘Just like an orchestra plays different instruments, neutron-star mergers emit gravitational waves through different modes,’ explains Prof Calderón Bustillo. ‘When the merging neutron stars are facing you, you will only hear the loudest instrument. However, if you are close to the merger’s orbital plane, you should also hear the secondary ones. This allows us to determine the inclination of the neutron-star merger, and better measure the distance’.

However, the method is not completely new: ‘We know this works well for the case of very massive black hole mergers because our current detectors can record the merger instant when the higher modes are most prominent. But in the case of neutron stars, the pitch of the merger signal is so high that our detectors can’t record it. We can only record the earlier orbits,’ says Prof Calderón Bustillo.

Future gravitational-wave detectors, like the proposed Australian project NEMO, will be able to access the actual merger stage of neutron stars. ‘When two neutron stars merge, the nuclear physics governing their matter can cause very rich signals that, if detected, could allow us to know exactly where the Earth sits with respect to the orbital plane of the merger,’ says co-author and OzGrav Chief Investigator Dr Paul Lasky, from Monash University. Dr Lasky is also one of the leads on the NEMO project. ‘A detector like NEMO could detect these rich signals,’ he adds.

In their study, the team performed computer simulations of neutron-star mergers that can reveal the effect of the nuclear physics of the stars on the gravitational waves. Studying these simulations, the team determined that a detector like NEMO could measure Hubble’s constant with a precision of 2%.
Co-author of the study Prof Tim Dietrich, from the University of Potsdam, says: ‘We found that fine details describing the way neutrons behave inside the star produce subtle signatures in the gravitational waves that can greatly help to determine the expansion rate of the Universe. It is fascinating to see how effects at the tiniest nuclear scale can infer what happens at the largest possible cosmological one’.

Samson Leong, undergraduate student at The Chinese University of Hong Kong and co-author of the study points out “one of the most exciting things about our result is that we obtained such a great improvement while considering a rather conservative scenario. While NEMO will indeed be sensitive to the emission of neutron-star mergers, more evolved detectors like Einstein Telescope or Cosmic Explorer will be even more sensitive, therefore allowing us to measure the expansion of the Universe with even better accuracy!”.

One of the most outstanding implications of this study is that it could determine if the Universe is expanding uniformly in space as currently hypothesised. ‘Previous methods to achieve this level of accuracy rely on combining many observations, assuming that the Hubble constant is the same in all directions and throughout the history of the Universe,’ says Calderón Bustillo. ‘In our case, each individual event would yield a very accurate estimate of “its own Hubble constant”, allowing us to test if this is actually a constant or if it varies throughout space and time.’

Featured image: Artist’s illustration of a pair of merging neutron stars. Credit: Carl Knox, OzGrav-Swinburne University

Reference: Juan Calderón Bustillo et al. Mapping the Universe Expansion: Enabling Percent-level Measurements of the Hubble Constant with a Single Binary Neutron-star Merger Detection, The Astrophysical Journal Letters (2021). DOI: 10.3847/2041-8213/abf502


O1/O2 Event Catalog The catalog of events and papers estimating their rates detected in LIGO-Virgo's first (O1) & second (O2) observation run are released

December 1 was an eventful day for gravitational wave astronomy as scientists attending the Gravitational Wave Physics and Astronomy Workshop in College Park, Maryland, presented new results from the National Science Foundation’s LIGO (Laser Interferometer Gravitational-Wave Observatory) and the European-based VIRGO gravitational-wave detector. The results were regarding their searches for merging cosmic objects such as pairs of black holes and pairs of neutron stars. The LIGO and Virgo collaborations have now confidently detected gravitational waves from 10 stellar-mass binary black hole mergers and one merger of neutron stars, which are the dense, spherical remains of stellar explosions. Six of the black hole merger events had been reported before, while four are newly announced!

Several Indian Gravitational-Wave researchers played important roles in these detections through the #IndIGO consortium, the Indian Initiative in Gravitational-wave Observations.

The second observing run, which ran from November 30, 2016 to August 25, 2017, yielded one binary neutron star merger and seven additional binary black hole mergers, including the four new gravitational-wave events being reported now! They are known as GW170729, GW170809, GW170818, and GW170823, in reference to the dates they were detected.

All these events are included in the new #o2catalog that was also released on Saturday! Some of these are record breaking events! For example, the new event GW170729, detected in the second observing run on July 29, 2017, is the most massive and distant gravitational-wave source ever observed! In this merger, which occurred roughly 5 billion years ago, an equivalent energy of almost five solar masses was converted into gravitational radiation!

GW170814 was the first binary black hole merger measured by the three-detector network, and allowed for the first tests of gravitational-wave polarisation (analogous to light polarisation).

The event GW170817, detected three days after GW170814, represented the first time that gravitational waves were ever observed from the merger of a binary neutron star system. What's more, this collision was seen in gravitational waves and light, marking an exciting new chapter in multi-messenger astronomy, in which cosmic objects are observed simultaneously in different forms of radiation.

One of the new events, GW170818, which was detected by the global network formed by the LIGO and Virgo observatories, was very precisely pinpointed in the sky. The position of the binary black holes, located 2.5 billion light-years from Earth, was identified in the sky with a precision of 39 square degrees. That makes it the next best localised gravitational-wave source after the GW170817 neutron star merger.

The scientific papers describing these new findings, which are being initially published on the arXiv repository of electronic preprints, present detailed information in the form of a catalog of all the gravitational wave detections and candidate events of the two observing runs as well as describing the characteristics of the merging black hole population. Most notably, we find that almost all black holes formed from stars are lighter than 45 times the mass of the Sun. Thanks to more advanced data processing and better calibration of the instruments, the accuracy of the astrophysical parameters of the previously announced events increased considerably.

As the results of the second observing run are released, all eyes are now on the third observing run which is starting in Spring 2019!


Merging boson stars could explain massive black hole collision and prove existence of dark matter

Artistic impression of the merger of two boson stars. Credit: Nicolás Sanchis-Gual and Rocío García Souto.

An international team of scientists led by the Galician Institute of High Energy Physics (IGFAE) and the University of Aveiro shows that the heaviest black hole collision ever observed, produced by the gravitational-wave GW190521, might actually be something even more mysterious: the merger of two boson stars. This would be the first evidence of the existence of these hypothetical objects, which are a candidate for dark matter, believed to comprise 27% of the mass in the universe.

Gravitational waves are ripples in the fabric of spacetime that travel at the speed of light. These originate in the most violent events of in the universe, carrying information about their sources. Since 2015, the two LIGO detectors in the U.S. and the Virgo detector in Cascina, Italy, have detected and interpreted gravitational waves. To date, these detectors have already observed around 50 gravitational-wave signals. All of these originated in the collisions and mergers of black holes and neutron stars, allowing physicists to deepen the knowledge about these objects.

However, the promise of gravitational waves goes much further than this, as these should eventually provide us with evidence for previously unobserved and even unexpected objects, and shed light on current mysteries like the nature of dark matter. The latter may, however, have already happened.

In September 2020, the LIGO and Virgo collaboration (LVC) announced to the world the gravitational-wave signal GW190521. According to their analysis, the signal was consistent with the collision of two heavy black holes, of 85 and 66 times the mass of the sun, which produced a final black hole with 142 solar masses. The resulting black hole was the first of a new, previously unobserved black hole family: intermediate-mass black holes. This discovery is of paramount importance, as such black holes were the missing link between two well-known black-hole families: stellar-mass black holes that form from the collapse of stars, and supermassive black holes that reside in the center of almost every galaxy, including the Milky Way.

In addition, this observation came with an enormous challenge. If what we think we know about how stars live and die is correct, the heaviest of the colliding black holes (85 solar masses) could not form from the collapse of a star at the end of its life, which opens up a range of doubts and possibilities about its origins.

In an article published today in Physical Review Letters, a team of scientists lead by Dr. Juan Calderón Bustillo at the Galician Institute of High Energy Physics (IGFAE), joint center of the University of Santiago de Compostela and Xunta de Galicia, and Dr. Nicolás Sanchis-Gual, a postdoctoral researcher at the University of Aveiro and the Instituto Superior Técnico (Univ. Lisboa), together with collaborators from University of Valencia, Monash University and The Chinese University of Hong Kong, has proposed an alternative explanation for the origin of the signal GW190521: the collision of two exotic objects known as boson stars, which are one of the most likely candidates to explain dark matter. In their analysis, the team was able to estimate the mass of a new particle constituent of these stars, an ultra-light boson with a mass billions of times smaller than electrons.

The team compared the GW190521 signal to computer simulations of boson-star mergers, and found that these actually explain the data slightly better than the analysis conducted by LIGO and Virgo. The result implies that the source would have different properties than stated earlier. Dr. Calderón Bustillo says, "First, we would not be talking about colliding black holes anymore, which eliminates the issue of dealing with a 'forbidden' black hole. Second, because boson star mergers are much weaker, we infer a much closer distance than the one estimated by LIGO and Virgo. This leads to a much larger mass for the final black hole, of about 250 solar masses, so the fact that we have witnessed the formation of an intermediate-mass black hole remains true."

Dr. Nicolás Sanchis-Gual says, "Boson stars are objects almost as compact as black holes but, unlike them, do not have a 'no-return' surface. When they collide, they form a boson star that can become unstable, eventually collapsing to a black hole, and producing a signal consistent with what LIGO and Virgo observed. Unlike regular stars, which are made of what we commonly know as matter, boson stars are made up of what we know as ultralight bosons. These bosons are one of the most appealing candidates for constituting what we know as dark matter."

The team found that even though the analysis tends to favor the merging black-holes hypothesis, a boson star merger is actually preferred by the data, although in a non-conclusive way. Prof. Jose A. Font from the University of Valencia says, "Our results show that the two scenarios are almost indistinguishable given the data, although the exotic boson star hypothesis is slightly preferred. This is very exciting, since our boson-star model is, as of now, very limited, and subject to major improvements. A more evolved model may lead to even larger evidence for this scenario and would also allow us to study previous gravitational-wave observations under the boson-star merger assumption."

This result would not only involve the first observation of boson stars, but also that of their building block, a new particle known as an ultra-light boson. Prof. Carlos Herdeiro from University of Aveiro says, "One of the most fascinating results is that we can actually measure the mass of this putative new dark-matter particle, and that a value of zero is discarded with high confidence. If confirmed by subsequent analysis of this and other gravitational-wave observations, our result would provide the first observational evidence for a long-sought dark matter candidate."


Black Hole-Neutron Star Mergers May Help Precisely Measure Universe’s Rate of Expansion

Gravitational-wave and electromagnetic observations of neutron-star-black-hole mergers can provide precise local measurements of the Universe’s rate of expansion. In new research, astrophysicists from Sweden, the United Kingdom and the Netherlands simulated over 25,000 such mergers, aiming to see how many would likely be detected by instruments on Earth.

The first artist’s illustration shows a key part of the process that created this new black hole, as the two neutron stars spin around each other while merging. The purple material depicts debris from the merger. Image credit: NASA / CXC / M.Weiss.

“The current expansion rate of the Universe — the Hubble constant, H0 — is at the heart of a significant cosmological controversy,” said University College London’s Dr. Stephen Feeney and colleagues.

“Direct measurements in the local Universe by the Cepheid-supernova distance ladder find H0 = 74.03 km per second per megaparsec.”

“This is discrepant from the 67.36 km per second per megaparsec value inferred from ESA’s Planck satellite’s observations of the Cosmic Microwave Background, the radiation left over from the Big Bang, suggesting our theory of the Universe may be wrong.”

“A third type of measurement, looking at the explosions of light and ripples in the fabric of space caused by black hole-neutron star collisions, should help to resolve this disagreement.”

In the study, the researchers simulated 25,241 scenarios of black holes and neutron stars colliding.

They found that, by 2030, instruments on Earth could sense ripples in space-time caused by up to 3,000 such mergers, and that for around 100 of these events, telescopes would also see accompanying explosions of light.

They concluded that this would be enough data to provide a new, completely independent measurement of the Universe’s rate of expansion, precise and reliable enough to confirm or deny the need for new physics.

“A neutron star is a dead star, created when a very large star explodes and then collapses, and it is incredibly dense – typically 20 km across but with a mass up to twice that of our Sun,” Dr. Feeney said.

“Its collision with a black hole is a cataclysmic event, causing ripples of space-time, known as gravitational waves, that we can now detect on Earth with observatories like LIGO and Virgo.”

“We have not yet detected light from these collisions. But advances in the sensitivity of equipment detecting gravitational waves, together with new detectors in India and Japan, will lead to a huge leap forward in terms of how many of these types of events we can detect. It is incredibly exciting and should open up a new era for astrophysics.”

“The disagreement over the Hubble constant is one of the biggest mysteries in cosmology,” added Professor Hiranya Peiris, also from University College London.

“In addition to helping us unravel this puzzle, the spacetime ripples from these cataclysmic events open a new window on the Universe. We can anticipate many exciting discoveries in the coming decade.”

The team’s results were published in the journal Physical Review Letters.

Stephen M. Feeney et al. 2021. Prospects for Measuring the Hubble Constant with Neutron-Star-Black-Hole Mergers. Phys. Rev. Lett 126 (17): 171102 doi: 10.1103/PhysRevLett.126.171102


Most massive neutron star near black hole tipping point

Pulses from a rapidly spinning neutron star are delayed slightly as they head toward Earth, passing through the distorted space around a companion white dwarf. That delay allowed researchers to calculate the mass of the pulsar. Image: BSaxton, NRAO/AUI/NSF

Astronomers have found the most massive neutron star yet discovered, a rapidly rotating pulsar orbiting in lockstep with a white dwarf that crams 2.17 solar masses into a city-size sphere just 30 kilometres (18.6 miles) across. The pulsar appears to be close to the tipping point between matter’s ability to resist the crush of gravity versus collapse into a black hole.

“Neutron stars are as mysterious as they are fascinating,” said Thankful Cromartie, a graduate student at the University of Virginia and a pre-doctoral fellow at the National Radio Astronomy Observatory in Charlottesville, Virginia. She is first author of a paper accepted by Nature Astronomy.

“These city-sized objects are essentially ginormous atomic nuclei. They are so massive that their interiors take on weird properties. Finding the maximum mass that physics and nature will allow can teach us a great deal about this otherwise inaccessible realm in astrophysics.”

Neutron stars and their fast-spinning cousins – pulsars – are formed in supernova explosions when the core of a massive star runs out of nuclear fuel. In the sudden absence of fusion energy radiating outward, gravity takes over and the core collapses, blowing away the star’s outer layers in spectacular fashion.

Depending on how much mass is present, the collapse will either halt due to quantum mechanical effects, leaving a compact neutron star in its wake, or continue to the point where a black hole forms.

Observations of gravity waves generated in the merger of two neutron stars suggests that tipping point is very close to 2.17 solar masses.

“Neutron stars have this tipping point where their interior densities get so extreme that the force of gravity overwhelms even the ability of neutrons to resist further collapse,” said Scott Ransom, an astronomer at NRAO and coauthor on the Nature Astronomy paper. “Each ‘most massive’ neutron star we find brings us closer to identifying that tipping point and helping us to understand the physics of matter at these mindboggling densities.”

The newly confirmed record holder is a millisecond pulsar known as J0740+6620. In a chance alignment, the pulsar and it’s white dwarf companion orbit each other edge on as seen from Earth.

Cromartie and her colleagues took advantage of that alignment to measure the mass of the white dwarf. Because the mass of the dwarf distorts the space around it in accordance with Einstein’s theory of general relativity, radiation from the pulsar is delayed on its way to Earth by about 10 millionths of a second when the pulsar passes behind its companion.

That delay was a direct indication of the white dwarf’s mass and from that, along with the time needed to make one rotation, the researchers could calculate the mass of the pulsar.

“The orientation of this binary star system created a fantastic cosmic laboratory,“ Ransom said.