Intermediate-mass black holes should help us to understand the evolutionary connection between stellar-mass and super-massive black holes1. However, the existence of intermediate-mass black holes is still uncertain, and their formation process is therefore unknown2. It has long been suspected that black holes with masses 100 to 10,000 times that of the Sun should form and reside in dense stellar systems3,4,5,6. Therefore, dedicated observational campaigns have targeted globular clusters for many decades, searching for signatures of these elusive objects. All candidate signatures appear radio-dim and do not have the X-ray to radio flux ratios required for accreting black holes7. Based on the lack of an electromagnetic counterpart, upper limits of 2,060 and 470 solar masses have been placed on the mass of a putative black hole in 47 Tucanae (NGC 104) from radio and X-ray observations, respectively8,9. Here we show there is evidence for a central black hole in 47 Tucanae with a mass of solar masses when the dynamical state of the globular cluster is probed with pulsars. The existence of an intermediate-mass black hole in the centre of one of the densest clusters with no detectable electromagnetic counterpart suggests that the black hole is not accreting at a sufficient rate to make it electromagnetically bright and therefore, contrary to expectations, is gas-starved. This intermediate-mass black hole might be a member of an electromagnetically invisible population of black holes that grow into supermassive black holes in galaxies.</s>All known black holes fall into two categories: small, stellar-mass black holes weighing a few Suns, and supermassive black holes weighing millions or billions of Suns. Astronomers expect that intermediate-mass black holes weighing 100 -- 10,000 Suns also exist, but so far no conclusive proof of such middleweights has been found. Today, astronomers are announcing new evidence that an intermediate-mass black hole (IMBH) weighing 2,200 Suns is hiding at the center of the globular star cluster 47 Tucanae.

"We want to find intermediate-mass black holes because they are the missing link between stellar-mass and supermassive black holes. They may be the primordial seeds that grew into the monsters we see in the centers of galaxies today," says lead author Bulent Kiziltan of the Harvard-Smithsonian Center for Astrophysics (CfA).

This work appears in the Feb. 9, 2017, issue of the science journal Nature.

47 Tucanae is a 12-billion-year-old star cluster located 13,000 light-years from Earth in the southern constellation of Tucana the Toucan. It contains thousands of stars in a ball only about 120 light-years in diameter. It also holds about two dozen pulsars that were important targets of this investigation.

47 Tucanae has been examined for a central black hole before without success. In most cases, a black hole is found by looking for X-rays coming from a hot disk of material swirling around it. This method only works if the black hole is actively feeding on nearby gas. The center of 47 Tucanae is gas-free, effectively starving any black hole that might lurk there.

The supermassive black hole at the center of the Milky Way also betrays its presence by its influence on nearby stars. Years of infrared observations have shown a handful of stars at our galactic center whipping around an invisible object with a strong gravitational tug. But the crowded center of 47 Tucanae makes it impossible to watch the motions of individual stars.

The new research relies on two lines of evidence. The first is overall motions of stars throughout the cluster. A globular cluster's environment is so dense that heavier stars tend to sink to the center of the cluster. An IMBH at the cluster's center acts like a cosmic "spoon" and stirs the pot, causing those stars to slingshot to higher speeds and greater distances. This imparts a subtle signal that astronomers can measure.

By employing computer simulations of stellar motions and distances, and comparing them with visible-light observations, the team finds evidence for just this sort of gravitational stirring.

The second line of evidence comes from pulsars, compact remnants of dead stars whose radio signals are easily detectable. These objects also get flung about by the gravity of the central IMBH, causing them to be found at greater distances from the cluster's center than would be expected if no black hole existed.

Combined, this evidence suggests the presence of an IMBH of about 2,200 solar masses within 47 Tucanae.

Since this black hole has eluded detection for so long, similar IMBHs may be hiding in other globular clusters. Locating them will require similar data on the positions and motions of both the stars and any pulsars within the clusters.</s>An intermediate-mass black hole might be lurking within a dense stellar cluster — a discovery that could point toward how these oddities form.

Every Friday Bülent Kızıltan heads to a local coffee shop. There, Kızıltan (Harvard-Smithsonian Center for Astrophysics), who is a self-described “overly curious person,” meets with scientists, artists and philosophers from different disciplines across the Cambridge and Boston area. His goal is to enrich himself intellectually.

That’s how he found himself deep in conversation with a cognitive scientist one afternoon who introduced him to a mathematical tool called Kullback–Leibler divergence. Originally developed by two mathematicians and cryptanalysts at the National Security Agency in the 1950s, the tool attempts to extract information from incomplete data.

Perhaps it was the stimulating effects of the freshly brewed cup of joe, but Kızıltan quickly realized that this tool could also be used when observing a dense stellar cluster — a messy environment chockfull of hundreds of thousands of stars where the center is hidden from view. It was the first step toward a paper published today in the journal Nature that provides the best evidence yet that a globular cluster might harbor an intermediate-mass black hole.

"Weighing" a Hidden Black Hole

Few intermediate-mass black holes have been observed before. In fact, skeptics might argue that none of these black holes — which theoretically lie in the range between those that are just a few times the mass of our Sun and those that weigh millions to billions of times the Sun — even exist.

The issue is two-fold. First, there’s no obvious, direct way for these objects to form. Second, the evidence that they exist has been hazy at best.

But with this new mathematical tool in hand, Kızıltan knew he could do better. He set his eyes on the globular cluster 47 Tucanae, located roughly 15,000 light-years away in the southern constellation Tucana. The cluster, which appears roughly the size of the full Moon, is one of the most massive globular clusters in the galaxy, with millions of stars.

In order to probe those stars, Kızıltan and his colleagues first built a realistic model of 47 Tucanae. Then, they measured the locations of 25 pulsars throughout the globular cluster. These rapidly rotating neutron stars sweep electromagnetic radiation across Earth with every spin at a rate so reliable they rival atomic clocks. This (plus the fact that they emit radio waves, as opposed to visible light) enabled the team to probe deeper into the typically invisible depths of the globular cluster.

The pulsars, they found, are on the move. They’re spinning around the center of the cluster rapidly — too rapidly given the number of central stars alone. Using their new mathematical tool, Kızıltan and his colleagues compared those pulsars’ oddly quick movements with their simulation in order to determine that an intermediate-mass black hole, some 2,200 times the mass of the Sun, must be lurking in the cluster’s center, governing the pulsars’ motions.

Runaway Collisions or Dangerous Tangos?

But Cole Miller (University of Maryland), who was not involved in the study, doesn’t think that the new evidence will convince every skeptic.

“Most scientists would like to see strong evidence,” he says. “Because if these objects exist, they will have implications for the formation of the earliest massive black holes. They will have implications about stellar dynamics. And they will have implications about the evolution of very massive stars. All of this is frontier research and you don't want to be jumping on the band wagon too early.”

The main issue is that astronomers are at a loss to explain how these intermediate-mass black holes can form. Miller’s favorite hypothesis enlists runaway stellar collisions. Essentially, the heaviest stars sink to the center of the globular cluster, where they are most likely to collide and merge with other heavy stars, forming even bigger stars. And because a star’s gravitational pull increases with its size and mass, so does its chance of further stellar collisions. This effect snowballs until a massive star rests in the center of the globular cluster.

But how this massive star evolves is not fully understood, says Kayhan Gültekin (University of Michigan) who was not involved in the study. “Standard stellar theory doesn’t apply to these objects. A lot of turning this merged star-like object into a black hole is based on analogies with stellar evolution rather than detailed calculations of how it would actually evolve.”

Luckily, the competing theory doesn’t need to invoke strange astrophysics. Here, stars evolve into black holes, which sink to the center of the cluster where one enters into a binary orbit with another. Through interactions with other black holes, that duo shrinks until it merges, creating a more massive black hole. This single black hole picks up another companion and the process begins anew, until there’s only one massive black hole in the center of the globular cluster.

Unfortunately, there are issues with this theory too. In the interactions between the black hole binary and the third black hole, energy is transferred to the third black hole. And if enough energy is transferred, the third black hole could get kicked out of the system entirely — a huge problem when you’re trying to build a massive black hole.

Although there are other theories that could explain how intermediate-mass black holes arise, only these two rely on the densely packed environment of a globular cluster.

“The fact that this black hole exists in 47 Tucanae, might mean that one or both of those theories is correct,” says Gültekin, who is hopeful that both theories will receive rejuvenated attention in light of the latest discovery.

Reference:

B. Kızıltan et al. “An Intermediate-Mass Black Hole in the Centre of the Globular Cluster 47 Tucanae.”Nature, February 9, 2017.</s>Black holes are among the most mysterious objects in the Universe. But they have one thing in common - most of the black holes we've found fall into two categories: small, stellar black holes with the mass a few times more than our Sun; or supermassive black holes that weigh the equivalent of millions of billions of Suns.

But researchers have just announced further evidence of a new type of black hole, called an 'intermediate-mass black hole', weighing a moderate 2,200 Suns, and hidden in a dense cluster of stars.

Researchers had previously predicted that these intermediate-mass black holes (IMBH), weighing between 100 to 10,000 Suns, could exist in our Universe.

But astronomers have only spotted a handful of IMBH candidates, so this new observation is pretty exciting.

Mid-sized black holes are thought to hold some important clues about how the supermassive black holes we see at the centres of galaxies today ended up getting so big - something that can't be easily explained by our current understanding of physics.

"We want to find intermediate-mass black holes because they are the missing link between stellar-mass and supermassive black holes," said lead researcher Bulent Kiziltan from the Harvard-Smithsonian Centre for Astrophysics.

"They may be the primordial seeds that grew into the monsters we see in the centres of galaxies today."

The new intermediate-mass black hole was spotted hiding at the centre of the globular star cluster known as 47 Tucanae.

47 Tucanae is located only 13,000 light-years from Earth - relatively close, in space terms - and contains the southern constellation of Tucana the Toucan.

The star cluster contains thousands of stars, and about two dozen pulsars, in a ball only about 120 light-years in diameter, and researchers have long been searching for signs of a black hole at its centre.

Black holes are thought to form when stars collapse in on themselves at the end of their lives, so with so many stars crammed into such a dense space, it seemed like a prime candidate.

But spotting a black hole in a globular star cluster is harder than it sounds, because black holes have such huge gravity that they suck up matter without allowing anything visible light to escape - hence the name "black".

Usually, astronomers spot black holes by looking for X-rays, which shoot out of the hot disk of material that surrounds black holes.

But the method only works when black holes are actively feeding on nearby gas. Because the centre of 47 Tucanae is gas-free, any black hole at its centre would effectively be starving, causing the black hole to remain hidden.

Another strategy would be to spot the black hole due to its influence on nearby stars - that's how we spotted the black hole at the centre of our galaxy - but because 47 Tucanae is so crowded, that didn't work either.

"Intermediate-mass black holes have been expected [in globular clusters] for many decades," Kiziltan told Space.com. "But we've not been able to find one conclusively."

In the new study, the team took two different approaches to finally nail down the IMBH. First, they monitored the overall motion of stars throughout the cluster rather than just looking at one or two.

The team noted that something dense was acting like a cosmic 'spoon' that was stirring the pot of stars, causing stars to slingshot to higher speeds and greater distances. The likeliest explanation for this activity was a black hole.

They backed up these observations by looking at the pulsars within the star cluster - pulsars are remnants of dead stars that send out bright blasts of radio signals.

The pulsars in 47 Tucanae were also getting flung about - something that couldn't be explained unless there was a black hole in their midst.

Using computer models, they were able to calculate that the globular star cluster must contain an intermediate-mass black hole about

Combined, the evidence suggests the presence of an IMBH weighing about 2,200 solar masses - taking into account the margin of error, the upper range of their calculations suggest it could be up to 3,700 solar masses, and as low as 1,400 solar masses.

All those numbers put it safely within the criteria of an IMBH.

The researchers will continue to study this new type of black hole to get some insight into how it works. But they think the technique could be used to find more IMBHs in the Universe - given how long this black hole eluded detection, the team suggests many other globular clusters could be hiding the unique objects.

The more we find, the closer we'll get to understanding how supermassive black holes came to be - and hopefully solving some of the other mysteries that surround how black holes work.

The research has been published in Nature.</s>This is an image of a series of Chandra images that has allowed scientists to trace the evolution of large-scale X-ray jets produced by a black hole in a binary star system. As the schematic shows, gaseous matter pulled from a normal star forms a disk around the black hole. The gas is heated to temperatures of millions of degrees, and intense electromagnetic forces in the disk can expel jets of high-energy particles. (Image for representation only. Please see actual image below.)

 

(Photo : NASA/Getty Images)

Astronomers identified for the first time an intermediate-mass black hole also called "middleweight" black hole hiding at the center of the globular star cluster 47 Tucanae. It weighs about 2,200 times the mass of the Sun.

The world's first discovery was described in the science journal Nature on Feb. 9, 2017. It was led by Dr. Bulent Kiziltan of the Harvard-Smithsonian Center for Astrophysics in the United States and other colleagues. This discovery is the first proof that the intermediate-mass black hole exists in space, according to ABC News.

Dr. Kiziltan said that they want to find intermediate-mass black holes because they are the missing link between stellar-mass and supermassive black holes. He further said that they may be primordial seeds that grew into the monsters they see in the centers of galaxies today.

There are two pieces of evidence of the existence of this middleweight black hole. First is the overall motions of stars in the cluster, in which it so dense that the heavier stars tend to sink at the center of the cluster. Meanwhile, the intermediate-mass black hole hiding at the center of the cluster acts like a cosmic spoon and stirs the pot. This caused the stars to slingshot to higher speeds and greater distances. Then, the team was able to employ computer simulations of stellar motions and distances and likened them with visible-light observations and finally finds evidence for this gravitational stirring.

The second evidence comes from pulsars and dead stars that radio signals could be easily identified. They were also flung by the gravity of the central intermediate-mass black hole and caused them to be at greater distances from the center of the cluster.

With these two pieces of evidence, the astronomers discovered the presence of an intermediate-mass black hole of about 2,200 solar masses in the 47 Tucanae. This is 12-billion-year-old star cluster located 13,000 lightyears away from Earth in the southern constellation of Tucana the Toucan, according to Phys.org.</s>Black holes are places of mystery. The laws of physics predict their existence but cannot explain what happens inside a black hole. Once we can do that, we will have stepped beyond the work of Albert Einstein and taken the next big leap in our understanding of the Universe.

Put simply, black holes are places where gravity is so strong that nothing can escape once it gets too close. This sets them apart from all other celestial objects, where you would always – in principle – be able to build a rocket strong enough to escape into space.

With a black hole, it would take an infinite amount of energy to pull away.

The boundary of no return is called the event horizon. Once across this invisible threshold you will be in the black hole’s clutches forever. It’s the celestial equivalent of a lobster pot – easy to get into but impossible to leave.

The concept of a black hole follows naturally from Albert Einstein’s General Theory of Relativity, published in 1915. It states that the strength of a celestial object’s gravitational field is determined by the density of matter it contains: the higher the density, the stronger the gravity.

The dilemma is where does this process stop? In a black hole, there is nothing known that can resist the overwhelming gravity, and we are forced to believe that the matter is simply crushed out of existence.

This is a dramatic way of describing a mathematical object called a singularity, a point of zero volume and infinite density. But physicists are unsure that such objects can exist in reality. It just sounds impossible.

Theories of quantum gravity are designed to tackle this problem and tell us how gravity behaves on the smallest possible scales, and at the great possible strengths and densities of matter. There are a number of approaches being taken, including the often mentioned string theory, but at present there is no strong front-runner.

A successful quantum gravity theory would not only allow astronomers to study the interior of a black hole, it would also tell us about the big bang, the origin of the universe. This is because the big bang is another place in nature where relativity predicts a singularity will appear.

In short, a quantum theory of gravity could tell us how the Universe came into existence in the first place, and that’s way astronomers are still so interested in black holes.

Stephen Hawking’s BBC Reith lectures can be heard here. An annotated transcript of the first lecture can be read here.

Stuart Clark is the author of The Unknown Universe (Head of Zeus), and co-host of the podcast The Stuniverse (Bingo Productions).</s>'Middleweight' black hole discovered in space in world-first, Queensland scientist says

A Queensland scientist has played a vital role in the world-first discovery of a "middleweight" black hole in space, spending 40 years searching the universe to find it.

University of Queensland astronomer Associate Professor Holger Baumgardt said it was the missing link between small and super-sized black holes.

Dr Baumgardt said the discovery would help astronomers understand galaxies and how galaxies have formed and evolved.

He said black holes were normally either small and weighed a few times the Sun's mass, or supermassive, and weigh millions of times the Sun's mass.

But this study showed the first proof of an intermediate-mass black hole existing — weighing 2,200 times the mass of the Sun.

The researchers, led by Dr Bulent Kiziltan of the Harvard-Smithsonian Centre for Astrophysics in the United States, relied on computer simulations by the Queensland scientists to look for clues in space.

By employing simulations of stellar motions and distances, and comparing them with visible-light observations, the team found evidence for just this sort of gravitational stirring.

He said the second line of evidence came from pulsars, compact remnants of dead stars with radio signals that were easily detectable.

"These objects were also flung about due to the gravitational influence of the central intermediate-mass black hole, causing them to be found at greater distances from the cluster's centre than would be expected if no black hole existed," Dr Baumgardt said.

The discovery was announced today in the journal Nature, revealing the black hole hid at the centre of the 12-billion-year-old globular 47 Tucanae star cluster.

It is 13,000 light years from Earth in the southern constellation of Tucana the Toucan.

It contains 3 million stars and holds about two dozen pulsars that are important targets of this investigation.

In their paper, the researchers said 47 Tucanae had been examined previously for a central black hole, without success.

Dr Kiziltan said in most cases, a black hole was found by looking for X-rays emanating from a hot disk of material swirling around the black hole.

This method only worked if the black hole was actively feeding on nearby gas.

"The centre of 47 Tucanae is gas-free, effectively starving any black hole that might lurk there," Dr Kiziltan said.

"A supermassive black hole at the centre of the Milky Way gives clues to its presence by its influence on nearby stars.

"Years of infrared observations have shown a handful of stars at our galactic centre whipping around an invisible object with a strong gravitational tug.

"But the crowded centre of 47 Tucanae makes it impossible to watch the motions of individual stars."

This was why the hunt for the "missing link" across the cosmos was so challenging, he said.

However, the discovery would not help find out more about life in space, Dr Baumgardt said.

"Anything which comes too close to the black hole will basically fall into the black hole and have no chance of ever getting out again."

The researchers said their discovery would help them unlock the link between the smaller mass black holes and super ones that could be found in the centre of galaxies.

"Of course we got very excited because we've been looking for black holes for a very long time," Dr Baumgardt said.

"We are already working on a second cluster to find a second 'middleweight' black hole."

Researchers said the fact this black hole had eluded detection for so long suggested black holes of similar masses could be hiding in other globular clusters.</s>Sometimes, you get lucky. There's a galaxy cluster that's been a frequent target of X-ray observatories due to the galaxies' interactions with the relatively dense gas in the vicinity. So, when a bright source of X-rays suddenly appeared behind this cluster, that brightness was imaged relatively quickly, and follow-up images have been captured regularly since then. Now, researchers are reporting that, a decade after the source of the X-rays first appeared, it's still around. That leaves just one likely explanation: the source is a supermassive black hole that's been devouring a star for all this time.

The source, 3XMM J150052.0+015452 (we'll stick with "the source" or "the object"), wasn't present when the region was first imaged in 2005. But it appeared in data obtained only four months later and has shown up in at least eight further observations since. Even at its first appearance, it was emitting energy the equivalent of over 1019 megatons every second, and it actually intensified considerably after that. Obviously, that implies something big.

Looking at visual images, the X-ray source appears to be centered on a small galaxy, roughly the size of the Large Magellanic Cloud that orbits the Milky Way. The researchers analyzing the data focus on the supermassive black hole at the center of this galaxy. Based on the galaxy's size, it would be a relatively "small" one, at about a million solar masses.

The area around black holes releases large amounts of energy when the black hole is drawing in matter. In the past, we've seen this power outbursts that last as long as a year. But this has been going for a decade, and is rather intense. As a result, the models we have that describe black hole feeding suggest that it's been exceeding a physical limit called the Eddington limit for the entire decade.

The Eddington Limit actually has something in common with the solar sails we discussed recently: photons that strike matter can impart a tiny bit of momentum to that matter. If the light is intense enough, it can actually repel the matter. As the matter falling into a black hole emits a lot of photons, it can create a pressure that keeps further matter from falling in. As more matter falls in, things eventually reach a point where the repulsive force starts to cut off the black hole's food supply.

So there's a limit to how much matter a black hole can swallow at once, called the Eddington limit (named after Arthur Eddington, the first man who tried to calculate its value). Given the mass of a black hole, we can calculate the Eddington limit and the amount of energy released as that matter falls in.

Doing so for our X-ray-emitting black hole suggests that it may have been exceeding the Eddington limit for at least a decade. We have seen things like this before, coming from black holes with masses similar to our Sun. But the amount of energy released by those black holes was much lower, and it generally tailed off within a year.

What could possibly supply a black hole with enough matter to last a decade? The researchers suggest that the object's gravity has torn a star apart and has been feeding on its remains. A star the size of the Sun, for example, would provide enough matter to feed a black hole of this size for up to two years. Scaling this up would imply that the star being swallowed by this object is massive, about 10 times the Sun's mass.

But it's also possible for different parts of the former star to interact as the black hole draws them in, extending out the period of high-level feeding. In this case, you don't need a star to be quite that big for feeding to last a decade. The researchers calculate that a star just twice the Sun's size would work for providing a decade of feeding, during which time the black hole would have swallowed the equivalent of the Sun's mass.

How can we tell the difference? If the culprit is a bigger star, the feeding could continue for quite some time, whereas a star twice the mass of the Sun would be largely digested by now. Recent observations suggest that the intensity of the X-ray emissions may be dropping off, which would be consistent with this. But the dimming is also consistent with a moving mass of gas somewhere between us and the black hole. We'll have to keep watching for a few more years to see what's going on with this object.</s>To say that straying too close to a black hole is a bad idea would be a massive understatement.

The extreme warping of spacetime caused by the black hole's intense gravity creates powerful tides that will rip any stars and planets to shreds, but only before spaghettifying them into oblivion. Generally, though, if a star gets turned into Silly Putty by a black hole's tides, the suffering is a short-lived and explosive affair, where some of the star stuff gets consumed and the rest is ejected back out into space.

For one unfortunate star, however, a massive black hole has been seen mauling its stellar entrails for a decade — ten times longer than it usually takes for a black hole to finish a star meal — possibly revealing how the biggest black holes grew to be so massive.

"We have witnessed a star's spectacular and prolonged demise," said Dacheng Lin from the University of New Hampshire in Durham, New Hampshire. "Dozens of tidal disruption events have been detected since the 1990s, but none that remained bright for nearly as long as this one."

By combining the observational power of three space telescopes — NASA's Chandra X-ray Observatory and Swift satellite, plus the European XMM-Newton — the drama has been seen unfolding in the center of a galaxy around 1.8 billion light-years away. Generating powerful X-rays, the tidal disruption event (TDE) — called XJ1500+0154 — has been telling astronomers the violent story of what happens when a star, roughly twice the mass of our sun, gets consumed by a supermassive black hole.

The event was first spotted by XMM-Newton July 23rd, 2005, and it reached peak brightness in a Chandra observation on June 5, 2008. Since then, the dimming X-ray emissions have been observed multiple times over the years, revealing a fascinating insight to how the most massive black holes consume matter and, perhaps, how they so quickly gained mass in the early universe.

"For most of the time we've been looking at this object, it has been growing rapidly," said James Guillochon, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., in a statement. "This tells us something unusual — like a star twice as heavy as our sun — is being fed into the black hole."



By measuring the X-ray emissions, astronomers have been able to gauge how efficiently the black hole has been able to consume the blended stellar material collecting in the black hole's accretion disk. In this case, it appears the stellar material from this TDE is still being consumed and models suggest X-ray emissions from this particular event will continue to dim over the next few years.

"This event shows that black holes really can grow at extraordinarily high rates," said Stefanie Komossa of QianNan Normal University for Nationalities in Duyun City, China. "This may help understand how precocious black holes came to be."

One of the biggest unsolved quastions hanging over modern cosmology is the known existence of supermassive black holes in the dawn of our universe — how did they become so massive so quickly? This new research about a strange TDE and one black hole's eating habits may hold at least part of the answer.</s>A giant black hole ripped apart a star and then gorged on its remains for about a decade, according to astronomers. This is more than ten times longer than any observed episode of a star’s death by black hole.

Researchers made this discovery using data from NASA’s Chandra X-ray Observatory and Swift satellite as well as ESA’s XMM-Newton. They published their findings February 6 in Nature Astronomy.

The trio of orbiting X-ray telescopes found evidence for a “tidal disruption event” (TDE), wherein the tidal forces due to the intense gravity from a black hole can destroy an object – such as a star – that wanders too close. During a TDE, some of the stellar debris is flung outward at high speeds, while the rest falls toward the black hole. As it travels inwards to be ingested by the black hole, the material heats up to millions of degrees and generates a distinct x-ray flare.

“We have witnessed a star’s spectacular and prolonged demise,” said Dacheng Lin from the University of New Hampshire in Durham, who led the study. “Dozens of tidal disruption events have been detected since the 1990s, but none that remained bright for nearly as long as this one.”

According to coauthor Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz, the observations of this TDE with a long-lasting bright phase fit the theoretical predications made in a 2015 paper he wrote with a former graduate student, coauthor James Guillochon, now at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

“We correctly predicted in advance of observations that some TDEs would be discovered with long-lived light curves,” Ramirez-Ruiz said. “The pieces of the star have to make an accretion disk promptly in order for the material to be digested by the black hole. With a lower mass black hole, stars can get disrupted farther away from the event horizon, and as a result we expect circularization and accretion to be slow.”

The extraordinary long bright phase of this event spanning over ten years means that a large amount of mass had to be digested by the black hole. The theoretical model supports either the complete digestion of a star with twice the mass of the sun, or the partial disruption of a much more massive star, Ramirez-Ruiz said, adding that he favors the full disruption of a lower mass star.

The X-ray source containing this force-fed black hole, known by its abbreviated name of XJ1500+0154, is located in a small galaxy about 1.8 billion light years from Earth.

The source was not detected in a Chandra observation on April 2nd, 2005, but was detected in an XMM-Newton observation on July 23rd, 2005, and reached peak brightness in a Chandra observation on June 5, 2008. These observations show that the source became at least 100 times brighter in x-rays. Since then, Chandra, Swift, and XMM-Newton have observed it multiple times.

The sharp x-ray vision of Chandra data shows that XJ1500+0154 is located at the center of its host galaxy, the expected location for a supermassive black hole. The x-ray data also indicate that radiation from material surrounding this black hole has consistently surpassed the so-called Eddington limit, defined by a balance between the outward pressure of radiation from the hot gas and the inward pull of the gravity of the black hole.

“For most of the time we’ve been looking at this object, it has been growing rapidly,” Guillochon said. “This tells us something unusual—like a star twice as heavy as our Sun—is being fed into the black hole.”

This TDE may help answer the question as to how supermassive black holes in the early universe grow. If supermassive black holes can grow from TDEs or other means faster than the Eddington limit, this could explain how supermassive black holes were able to reach masses about a billion times higher than the sun when the universe was only about a billion years old.

“This event shows that black holes really can grow at extraordinarily high rates,” said co-author Stefanie Komossa of QianNan Normal University for Nationalities in Duyun City, China. “This may help understand how precocious black holes came to be.”

Based on the modeling by the researchers, the black hole’s feeding supply should be significantly reduced in the next decade. This would result in XJ1500+0154 fading in x-ray brightness over the next several years.

NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra’s science and flight operations.
New strong evidence supporting the existence of an intermediate-mass black hole is announced.