Stars Orbiting Close to Black Holes Flattened like Hot Pancakes

A star orbiting a black hole (NASA)

Playing with black holes is a risky business, especially for a star that is unlucky enough to be orbiting one. Assuming an unfortunate star hasn’t already had all of its hydrogen fuel and other component elements stripped from its surface, the powerful tidal forces will have some fun with the doomed stellar body. First the star will be stretched out of shape and then it will be flattened like a pancake. This action will compress the star generating violent internal nuclear explosions, and shockwaves will ripple throughout the tormented stellar plasma. This gives rise to a new type of X-ray burst, revealing the sheer power a black hole’s tidal radius has on the smaller binary sibling. Sounds painful…

It is intriguing to try to understand the dynamics near a supermassive black hole, especially when a star strays too close. Recent observations of a distant galaxy suggests the material pulled from a star near the center of a galactic nucleus caused a powerful X-ray flare which echoed from the surrounding molecular torus. The infalling stellar gas was sucked into the black hole’s accretion disk, generating a huge quantity of energy as a flare. Whether or not the star stayed intact for the duration of its death-spiral into the supermassive black hole it is unknown, but scientists have been working on a new model of a star orbiting a black hole weighing in at a few million solar masses (assuming the star can hold it together for that long).

The pancake effect of a star falling into the tidal radius of a black hole (J.-P. Luminet)

Matthieu Brassart and Jean-Pierre Luminet of the Observatoire de Paris-Meudon, France, are studying the effects of the tidal radius on a star orbiting close to a supermassive black hole. The tidal radius of a supermassive black hole is the distance at which gravity will have a far greater pull on the leading edge of the star than the following edge. This massive gravitational gradient causes the star to be stretched beyond recognition. What happens next is a little strange. In a matter of hours, the star will swing around the black hole, through the tidal radius, and out the other end. But according to the French scientists, the star that comes out isn’t the same as the star that went in. The star deformation is described in the accompanying diagram and detailed below:

  • (a)-(d): Tidal forces are weak and the star remains practically spherical.
  • (e)-(g): Star falls into the tidal radius. This is the point at which it is destined to be destroyed. It undergoes changes in its shape, first “cigar shaped”, then it gets squeezed as the tidal forces flatten the star in its orbital plane to the shape of a pancake. Detailed hydrodynamical simulations of shock wave dynamics have been carried out during this “crushing phase”.
  • (h): After swinging around the point of closest approach in its orbit (perihelion), the star rebounds, leaving the tidal radius and begins to expand. Leaving the black hole far behind, the star breaks up into clouds of gas.

As the star is dragged around the black hole in the “crushing phase” it is believed that the pressures will be so great on the deformed star that intense nuclear reactions will occur throughout, heating it up in the process. This research also suggests powerful shock waves will travel through the hot plasma. The shock waves would be powerful enough to produce a short (<0.1 second) blast of heat (>109 Kelvin) propagating from the star’s core to its deformed surface, possibly emitting a powerful X-ray flare or gamma-ray burst. Due to this intense heating, it seems possible that most of the stellar material will escape the black holes gravitational pull, but the star will never be the same again. It will be transformed into vast clouds of turbulent gas.

This situation wouldn’t be too hard to imagine when considering the dense stellar volume in galactic nuclei. In fact, Brassart and Luminet have estimated that there may be 0.00001 event per galaxy, and although this may seem low, future observatories such as the Large Synoptic Survey Telescope (LSST) may detect these explosions, possibly several per year as the Universe is transparent to hard X-ray and gamma-ray emissions.

Source: Science Daily

Supermassive Black Hole Kicked Out of Galaxy: First Ever Observation

Colliding galaxies can force the supermassive black holes in their cores together (NCSA)

For the first time, the most extreme collision to occur in the cosmos has been observed. Galaxies are known to hide supermassive black holes in their cores, and should the galaxies collide, tidal forces will cause massive disruption to the stars orbiting around the galactic cores. If the cores are massive enough, the supermassive black holes may become trapped in gravitational attraction. Do the black holes merge to form a super-supermassive black hole? Do the two supermassive black holes spin, recoil and then blast away from each other? Well, it would seem both are possible, but astronomers now have observational evidence of a black hole being blasted away from its parent galaxy after colliding with a larger cousin.

Most galaxies in the observable universe contain supermassive black holes in their cores. We know they are hiding inside galactic nuclei as they have a huge gravitational dominance over that region of space, sucking away at stars orbiting too close. Recent observations of galactic cores show quickly rotating stars around something invisible. Calculating the star orbital velocities, it has been deduced that the invisible body they are orbiting is something very massive; a supermassive black hole of hundreds of millions of solar masses. They are also the source of bright quasars in active, young galaxies.

Now, the same research group who made the astounding discovery of the structure of a black hole molecular torus by analysing the emission of echoed light from an X-ray flare (originating from star matter falling into the supermassive black hole’s accretion disk) have observed one of these supermassive black holes being kicked out of its parent galaxy. What caused this incredible event? A collision with another, bigger supermassive black hole.

A cartoon of a superkick (MPE/HST)

Stefanie Komossa and her team from the Max Planck Institute for extraterrestrial Physics (MPE) made the discovery. This work, to be published in Astrophysical Journal Letters on May 10th, verifies something that has only been modelled in computer simulations. Models predict that as two fast-rotating black holes begin to merge, gravitational radiation is emitted through the colliding galaxies. As the waves are emitted mainly in one direction, the black holes are thought to recoil – much like the force that accompanies firing a rifle. The situation can also be thought of as two spinning tops, getting closer and closer until they meet. Due to their high angular momentum, the tops experience a “kick”, very quickly ejecting the tops in the opposite directions. This is essentially what two supermassive black holes are thought to do, and now this recoil has been observed. What’s more, the ejected black hole’s velocity has been measured by analysing the broad spectroscopic emission lines of the hot gas surrounding the black hole (its accretion disk). The ejected black hole is travelling at a velocity of 2650 km/s (1647 mi/s). The accretion disk will continue to feed the recoiled black hole for many millions of years on its journey through space alone.

Supporting the evidence that this is indeed a recoiling supermassive black hole, Komossa analysed the parent galaxy and found hot gas emitting X-rays from the location where the black hole collision took place.

Now Komossa and her team hope to answer the questions this discovery has created: Did galaxies and black holes form and evolve jointly in the early Universe? Or was there a population of galaxies which had been deprived of their central black holes? And if so, how was the evolution of these galaxies different from that of galaxies that retained their black holes?

It is hoped that the combined efforts of observatories on Earth and in space may be used to find more of these “superkicks” and begin to answer these questions. The discovery of gravitational waves will also help, as this collision event is predicted to wash the Universe in powerful gravitational waves.

Source: MPE News

Magnetic Fields Shape the Jets Pouring Out of Supermassive Black Holes (with video)

Artist's impression of a supermassive black hole. Credit: NRAO

The cores of galaxies contain supermassive black holes, containing hundreds of millions of times the mass of Sun. As matter falls in, it chokes up, forming a super hot accretion disk around the black hole. From this extreme environment, the black hole-powered region spews out powerful jets of particles moving at the speed of light. Astronomers have recently gotten one of the best views at the innermost portion of the jet.

A team of astronomers led by Alan Marscher, of Boston University, used the National Radio Astronomy Observatory’s Very Long Baseline Array (VLBA) to peer at the central region of a galaxy called BL Lacertae.

“We have gotten the clearest look yet at the innermost portion of the jet, where the particles actually are accelerated, and everything we see supports the idea that twisted, coiled magnetic fields are propelling the material outward,” said Alan Marscher, of Boston University, leader of an international research team. “This is a major advance in our understanding of a remarkable process that occurs throughout the Universe,” he added.

Here’s how the theory goes. As material falls into the supermassive black hole faster than it can consume it, an accretion disk forms. This is a flattened, rotating disk that circles the black hole. The spinning interaction with the black hole creates powerful magnetic fields that twist and form into a tightly-coiled bundle. It’s these magnetic fields that blast out particles into focused beams.

The theorists expected that the region inside the acceleration region would follow a corkscrew-shaped path inside the twisting magnetic fields. Furthermore, researchers expected that light and material would brighten when it was pointed directly towards Earth. And finally, the astronomers expected that there should be a flare when material hits a stationary shock wave called the “core” after it comes out of the acceleration region.

And that’s just what the observations show. The VLBA was used to study how a knot of material was ejected out of the black hole’s environment. As the knot moved through the stationary shock wave, it flared just as the theorists had predicted.

Original Source: NRAO News Release

X-Ray Flare Echo Reveals Supermassive Black Hole Torus

The echo of X-ray emissions from a black hole swallowing a star can be observed as light echos (MPE/ESA)

The light echo of an X-ray flare from the nucleus of a galaxy has been observed. The flare almost certainly originates from a single star being gravitationally ripped apart by a supermassive black hole in the galactic core. As the star was being pulled into the black hole, its material was injected into the black hole accretion disk, causing a sudden burst of radiation. The resulting X-ray flare emission was observed as it hit local stellar gases, producing the light echo. This event gives us a better insight to how stars are eaten by supermassive black holes and provides a method to map the structure of galactic nuclei. Scientists now believe they have observational evidence for the elusive molecular torus that is thought to surround active supermassive black holes.

Light echoes from distant galaxies have been observed before. The echoes from a supernova that occurred 400 years ago (that is now observed as the supernova remnant SNR 0509-67.5) were only just observed here on Earth, after the supernova emissions bounced off galactic matter. This is the first time however that the energetic emissions from a sudden influx of matter into a supermassive black hole accretion disk has been observed echoing off gases within galactic nuclei. This is a major step toward understanding how stars are consumed by supermassive black holes. Additionally, the echo acts like a searchlight, highlighting the dark stellar matter between the stars, revealing a structure we have never seen before.

This new research was carried out by an international team led by Stefanie Komossa from the Max Planck Institute for extraterrestrial Physics in Garching, Germany, using data from the Sloan Digital Sky Survey. Komossa likens this observation to illuminating a dark city with a firework burst:

To study the core of a normal galaxy is like looking at the New York skyline at night during a power failure: You can’t learn much about the buildings, roads and parks. The situation changes, for example, during a fireworks display. It’s exactly the same when a sudden burst of high-energy radiation illuminates a galaxy.” – Stefanie Komossa

A strong X-ray burst such as this can be very hard to observe as they are short-lived emissions, but a huge amount of information can be gained by seeing such an event if astronomers are quick enough. By analysing the degree of ionization and velocity data in the spectroscopic emission lines of the echoed light, the Max Planck physicists were able to deduce the flare location. Held within the emission lines are the cosmic “fingerprints” of the atoms at the source of the emission, leading them to the galactic core where a supermassive black hole is believed to live.

A molecular torus surrounding a supermassive black hole (NASA/ESA)

The standard model for galactic nuclei (a.k.a. unified model of active galaxies) predict a “molecular torus” surrounding the black hole accretion disk. These new observations of the galaxy named SDSSJ0952+2143 appear to show the X-ray flare was reflected by the galactic molecular torus (with strong iron emission lines). This is the first time the presence of a possible torus has been seen, and if confirmed, astrophysicists will have their observational evidence of this theoretical possibility, strengthening the standard model. What’s more, using accretion disk flares may aid scientists when attempting to map the structure of other molecular toruses.

Strengthening the observation of echoed X-ray emission from the torus is the possibility of seeing variable infrared emissions. This emission signifies a “last call for help” by the dusty cloud being rapidly heated by the incident X-rays. The dust will have been vaporized soon after.

But how do they know it was a star that fell into the accretion disk? In addition to the strong iron lines, there are strange hydrogen emission lines which have never been seen before. This is a strong piece of evidence that it is the debris from a star that came too close to the black hole, stripping away its hydrogen fuel.

Although the X-ray flare has subsided, the galaxy continues to be observed by the X-ray satellite Chandra. Faint but measurable X-ray emissions are being observed perhaps signifying that the star is still being fed to the accretion disk. It seems possible that measuring this faint emission may also be of use, allowing researchers to continue to map the molecular torus long after the initial strong X-ray emission has ended.

Sources: arXiv, Max Planck Institute for Extraterrestrial Physics

Why are there Black Holes in the Middle of Galaxies?

Question: Why are Black Holes in the Middle of Galaxies?

Answer: The black holes you’re thinking of are known as supermassive black holes. Stellar mass black holes are created when a star at least 5 times larger than the Suns out of fuel and collapses in on itself forming a black hole. The supermassive black holes, on the other hand, can contain hundreds of millions of times the mass of a star like our Sun.

Astronomers are now fairly certain that these supermassive black holes are at the heart of almost every galaxy in the Universe. Furthermore, the mass of these black holes is somehow tied to the mass of the rest of the galaxy. They grown in tandem with each other.

When large quantities of material falls into the black hole, it chokes up, unable to get consumed all at once. This “accretion disk” begins to heat up and blaze brightly in many different wavelengths, including X-rays. When supermassive black holes are actively feeding, astronomers call these quasars.

So how do these black holes get there in the first place? Astronomers aren’t sure, but it could be that the dark matter halo that surrounds every galaxy serves to focus and concentrate material as the galaxy was first forming. Some of this material became the supermassive black hole, while the rest became the stars of the galaxy. It’s also possible that the black hole formed first, and collected the rest of the galaxy around it.

Astronomers just don’t know.

Milky Way’s Black Hole Gave Off a Burst 300 Years Ago

Sagittarius A*. Image credit: Chandra

Our Milky Way’s black hole is quiet – too quiet – some astronomers might say. But according to a team of Japanese astronomers, the supermassive black hole at the heart of our galaxy might be just as active as those in other galaxies, it’s just taking a little break. Their evidence? The echoes from a massive outburst that occurred 300 years ago.

The astronomers found evidence of the outburst using ESA’s XMM-Newton space telescope, as well as NASA and Japanese X-ray satellites. And it helps solve the mystery about why the Milky Way’s black hole is so quiet. Even though it contains 4 million times the mass of our Sun, it emits a fraction of the radiation coming from other galactic black holes.

“We have wondered why the Milky Way’s black hole appears to be a slumbering giant,” says team leader Tatsuya Inui of Kyoto University in Japan. “But now we realize that the black hole was far more active in the past. Perhaps it’s just resting after a major outburst.”

The team gathered their observations from 1994 to 2005. They watched how clouds of gas near the central black hole brightened and dimmed in X-ray light as pulses of radiation swept past. These are echoes, visible long after the black hole has gone quiet again.

One large gas cloud is known as Sagittarius B2, and it’s located 300 light-years away from the central black hole. In other words, radiation reflecting off of Sagittarius B2 must have come from the black hole 300 years previously.

By watching the region for more than 10 years, the astronomers were able to watch an event wash across the cloud. Approximately 300 years ago, the black hole unleashed a flare that made it a million times brighter than it is today.

It’s hard to explain how the black hole could vary in its radiation output so greatly. It’s possible that a supernova in the region plowed gas and dust into the vicinity of the black hole. This led to a temporary feeding frenzy that awoke the black hole and produced the great flare.

Original Source: ESA News Release

What Happens When Three Black Holes Collide?

A computer simulation of two black holes colliding, what happens if three collide? (credit: EU Training Network)

The consequences of two black holes colliding may be huge, the energy produced by such a collision could even be detected by observatories here on Earth. Ripples in space-time will wash over the Universe as gravitational waves and are predicted to be detected as they pass through the Solar System. Taking this idea one step further, what would happen if three black holes collide? Sound like science fiction? Well it’s not, and there is observational evidence that three black holes can cluster together, possibly colliding after some highly complex orbits that can only be calculated by the most powerful computers available to researchers…

Back in January 2007, a quasar triplet was observed over 10 billion light years away. Quasars are generated by the supermassive black holes eating away at the core of active galaxies. Using the powerful W. M. Keck Observatory, researchers from Caltech were able to peer back in time (10 billion years) to see a period in the Universe’s life when active galaxies and black hole mergers would have been fairly common events (when compared to the calmer Universe of today). They observed three tightly packed quasars, an unprecedented discovery.

Now, scientists Manuela Campanelli, Carlos Lousto and Yosef Zlochower, all working at Rochester Institute of Technology’s Center for Computational Relativity and Gravitation, have simulated the highly complex mechanisms behind three interacting and merging supermassive black holes, much like the situation observed by Keck in 2007. The same group have worked on calculating the collision of two black holes before and have written a code that is powerful enough to simulate the collision of up to 22 black holes. However, 22 black holes probably wouldn’t collide naturally, this simply demonstrates the stability of the code, “Twenty-two is not going to happen in reality, but three or four can happen,” says Yosef Zlochower, an assistant professor. “We realized that the code itself really didn’t care how many black holes there were. As long as we could specify where they were located – and had enough computer power – we could track them.

These simulations are of paramount importance to the gravitational wave detectors such as the Laser Interferometer Gravitational-Wave Observatory (LIGO). So far there has been no firm evidence to come from these detectors, but more time is needed, the LIGO detector requires several years of “exposure time” to collect enough data and remove observational “noise”. But what do gravitational wave astronomers look for? This is the very reason many different cosmic scenarios are being simulated so the characteristics of events like two or three black holes mergers can be identified from their gravitational wave signature.

Gravitational wave astronomers “need to know what to look for in the data they acquire otherwise it will look like just noise. If you know what to look for you can confirm the existence of gravitational waves. That’s why they need all these theoretical predictions.” – Manuela Campanelli, director of RIT’s Center for Computational Relativity and Gravitation.

Source: RIT University News

Star Formation Extinguished by Quasars


According to new research, a galaxy with a quasar in the middle is not a good place to grow up. As active galactic nuclei (AGN) evolve, they pass through a “quasar phase”, where the accretion disk surrounding the central black hole blasts intense radiation into space. The quasar far outshines the entire host galaxy. After the quasar phase, when the party is over, it is as if there is no energy left and star formation stops.

AGN are the compact, active and bright central cores to active galaxies. The intense brightness from these active galactic cores is produced by the gravitationally driven accretion disk of hot matter spinning and falling into a supermassive black hole at the centre. During the lifetime of an AGN, the black hole/accretion disk combo will undergo a “quasar phase” where intense radiation is blasted from the superheated gases surrounding the black hole. Typically quasars are formed in young galaxies.
Multicolour SDSS optical images of NGC5806 and NGC5750, nearby spiral galaxies with active nuclei similar to those being studied by Westoby and his collaborators. Image credit: The Sloan Digital Sky Survey
Although the quasar phase is highly energetic and tied with young galaxy formation, according to new results from the Sloan Digital Sky Survey, it also marks the end for any further star birth in the galaxy. These findings will be presented today (Friday 4th April) at the RAS National Astronomy Meeting in Belfast, Northern Ireland, by Paul Westoby having just completed a study of 360 000 galaxies in the local Universe. He carried out this research with Carole Mundell and Ivan Baldry from the Astrophysics Research Institute of Liverpool, John Moores University, UK. This study was proposed to understand the relationship between accreting black holes, the birth of stars in galactic cores and the evolution of galaxies as a whole. The results are astonishingly detailed.

By analysing so many galaxies, quite a detailed picture emerges. The primary result to come from this shows that as a young galactic core is dominated by a highly energetic quasar, star formation stops. After this phase in a galaxy’s life, star formation is not possible; the remaining stars are left to evolve by themselves.

An artists impression of a quasar (credit: NASA)

It is believed that all AGNs go through the quasar phase in their early galactic lives. It is also thought that most massive galaxies will have a supermassive black hole hiding inside their galactic cores passively, having already gone through the quasar phase. Westoby notes that some dormant supermassive black holes can be “reignited” into a secondary quasar phase, but the mechanisms behind this are sketchy.

The starlight from the host galaxy can tell us much about how the galaxy has evolved […] Galaxies can be grouped into two simple colour families: the blue sequence, which are young, hotbeds of star-formation and the red sequence, which are massive, cool and passively evolving..” – Paul Westoby.

It is found there is a sudden cut-off point for star formation, and this occurs right after the quasar phase. After the quasar phase, the AGN relaxes into a quieter state, there is no star formation and gradual evolution of stars progresses into the “red sequence” of star evolution.

Other findings include the indication that regardless of the size of the galaxy, it is the shape of the galactic “bulge” that matters. Without a large classical bulge in the centre, supermassive black holes that drive the AGN are not possible. Therefore, only galaxies with a bulge have AGN at the core. Another factor affecting supermassive black hole formation is the density of galaxies in a volume of space. Should there be too many, supermassive black holes become a scarcity.

Source: The RAS National Astronomy Meeting 2008

A Black Hole Observed in the Heart of Mysterious Omega Centauri

Omega Centauri is a strange thing. It’s been classified as a star, then a nebula, then a globular cluster and now it’s thought to be a dwarf galaxy missing its outer stars. Why is it in such a mess? How can this oddball galaxy be explained? New research suggests it has an intermediate-black hole living in its core, giving astronomers the best idea yet as to where supermassive black holes come from. Omega Centauri might hold one of the most profound secrets as to how the largest objects in the observable universe are born…

The stars within Omega Centauri (credit: ESA/NASA)
Two thousand years ago, Omega Centauri was classified as a single star by Ptolemy. Edmond Halley studied this “star” but thought it looked a bit diffuse and re-classified it as a nebula in 1677. Then, in the 1830s, John Herschel was the first astronomer to realize this “nebula” was actually a galaxy, a globular cluster galaxy. But now, new observations by the Hubble Space Telescope (HST) reveal that this “globular cluster” isn’t what it seems… it’s actually a dwarf galaxy, stripped of its outer stars, some 17,000 light years away.

See an observation video zooming into the location of Omega Centauri in the constellation of Centaurus.

So what led to astronomers thinking there was something strange about this cosmic collection of stars? It rotates faster than other globular clusters, it is strangely flat and it contains stars of many generations (globular clusters usually contain stars of one generation). These reasons plus the fact Omega Centauri is ten times bigger than the largest globular clusters have led scientists to believe that this was no ordinary galaxy.

The constellation of Centaurus, where the globular cluster Omega Centauri is located (credit: ESA/NASA)

The main theory is that this unlucky galaxy may have crashed into the Milky Way in the distant past, shedding its outermost stars during the collision. This explains the lack of stars in its outer region. But why is it rotating so quickly, especially in the center?

These stunning images were taken by the NASA/ESA Hubble Space Telescope, which continues to do amazing science after 18 years in orbit. Combined with ground-based observations by the Gemini South telescope in Chile, astronomers have been able to deduce that a black hole may be at the root of a lot of the anomalies seen in Omega Centauri.

The research carried out at the Max-Planck Institute for Extraterrestrial Physics (in Garching, Germany), headed by Eva Noyola, shows stars near the center of Omega Centauri orbiting something very fast. In fact, this something is invisible for a reason. Calculating this invisible object’s mass, it is most likely that the group are observing an intermediate-size black hole with the mass of 40,000 solar masses. They have investigated other possibilities, perhaps the fast-orbiting stars could be accelerated by the collective mass of small, weakly radiating bodies such as white dwarves, or the orbiting stars’ have highly elliptical orbits and the point of closest approach is currently being observed, giving the impression they are going faster. However, the intermediate-size black hole theory appears to fit the situation far better.

This is a highly significant discovery, as so far there has been little linking the smaller, stellar black holes with the supermassive ones that sit in the center of large galaxies such as our own. There have been many theories put forward about how these huge black holes may have formed, but to find an intermediate-sized black hole may be the missing link and will help astrophysicists understand how supermassive black holes are “seeded” in the first place.

This result shows that there is a continuous range of masses for black holes, from supermassive, to intermediate-mass, to small stellar mass types […] We may be on the verge of uncovering one possible mechanism for the formation of supermassive black holes. Intermediate-mass black holes like this could be the seeds of full-sized supermassive black holes.” – Eva Noyola.


Astronomers Find the Smallest Black Hole


Black holes seem to have no upper limit; some weigh in at hundreds of millions of times the mass of the Sun. But how small can they be? Astronomers have discovered what they think is the least massive black hole ever seen, with a mere 3.8 times the mass of the Sun, and a diameter of only 25 km (15 miles) across.

The announcement was made by Nikolai Shaposhnikov of NASA’s Goddard Space Flight Center and his colleagues at the American Astronomical Society High-Energy Astrophysics Division currently being held in Los Angeles, California.

The “tiny” black hole, known as XTE J1650-500, was discovered back in 2001 in a binary system with a normal star. Astronomers had known about the binary system for several years, but they were finally able to make accurate measurements using NASA’s Rossi X-ray Timing Explorer (RXTE) to pin down the mass.

Although black holes themselves are invisible, they’re often surrounded by a disk of hot gas and dust – material chokes up, like water going down the drain. As the hot gas builds up, it releases torrents of X-rays at regular intervals.

Astronomers have long suspected that the frequency of these X-ray blasts depend on the mass of the stars. As the mass of the black hole increases, the size of the accretion disk expands outward too; there are less frequent X-ray emissions.

By cross referencing this method with other, established techniques for weighing black holes, the team is very confident that they’ve got the trick to measuring black hole mass.

When they applied their technique to XTE J1650-500, they turned up a mass of 3.8 Suns, give or take half a solar mass. This is dramatically smaller than the previous record holder at 6.3 Suns.

What’s the smallest possible black hole? Astronomers think it’s somewhere between 1.7 and 2.7 solar masses. Smaller than that and you get a neutron star. Finding black holes that approach this lower limit will help physicists better understand how matter behaves when its crushed down in this extreme environment.

Original Source: NASA News Release