X-ray pulse detected near event horizon as black hole devours star

X-ray pulse detected near event horizon as black hole devours star
This artist's impression shows hot gas orbiting in a disk around a rapidly-spinning black hole. The elongated spot depicts an X-ray-bright region in the disk, which allows the spin of the black hole to be estimated. Credit: NASA/CXC/M. Weiss

On Nov. 22, 2014, astronomers spotted a rare event in the night sky: A supermassive black hole at the center of a galaxy, nearly 300 million light years from Earth, ripping apart a passing star. The event, known as a tidal disruption flare, for the black hole's massive tidal pull that tears a star apart, created a burst of X-ray activity near the center of the galaxy. Since then, a host of observatories have trained their sights on the event, in hopes of learning more about how black holes feed.

Now researchers at MIT and elsewhere have pored through data from multiple telescopes' observations of the event, and discovered a curiously intense, stable, and periodic pulse, or signal, of X-rays, across all datasets. The signal appears to emanate from an area very close to the black hole's event horizon—the point beyond which material is swallowed inescapably by the black hole. The signal appears to periodically brighten and fade every 131 seconds, and persists over at least 450 days.

The researchers believe that whatever is emitting the periodic signal must be orbiting the black hole, just outside the event horizon, near the Innermost Stable Circular Orbit, or ISCO—the smallest orbit in which a particle can safely travel around a black hole.

Given the signal's stable proximity to the black hole, and the black hole's mass, which researchers previously estimated to be about 1 million times that of the sun, the team has calculated that the black hole is spinning at about 50 percent the speed of light.

The findings, reported today in the journal Science, are the first demonstration of a tidal disruption flare being used to estimate a black hole's spin.

The study's first author, Dheeraj Pasham, a postdoc in MIT's Kavli Institute for Astrophysics and Space Research, says that most supermassive black holes are dormant and don't usually emit much in the way of X-ray radiation. Only occasionally will they release a burst of activity, such as when stars get close enough for black holes to devour them. Now he says that, given the team's results, such tidal disruption flares can be used to estimate the spin of supermassive black holes—a characteristic that has been, up until now, incredibly tricky to pin down.

"Events where black holes shred stars that come too close to them could help us map out the spins of several supermassive black holes that are dormant and otherwise hidden at the centers of galaxies," Pasham says. "This could ultimately help us understand how galaxies evolved over cosmic time."

Pasham's co-authors include Ronald Remillard, Jeroen Homan, Deepto Chakrabarty, Frederick Baganoff, and James Steiner of MIT; Alessia Franchini at the University of Nevada; Chris Fragile of the College of Charleston; Nicholas Stone of Columbia University; Eric Coughlin of the University of California at Berkeley; and Nishanth Pasham, of Sunnyvale, California.

A real signal

Theoretical models of tidal disruption flares show that when a black hole shreds a star apart, some of that star's material may stay outside the event horizon, circling, at least temporarily, in a stable orbit such as the ISCO, and giving off periodic flashes of X-rays before ultimately being fed by the black hole. The periodicity of the X-ray flashes thus encodes key information about the size of the ISCO, which itself is dictated by how fast the black hole is spinning.

Pasham and his colleagues thought that if they could see such regular flashes very close to a black hole that had undergone a recent tidal disruption event, these signals could give them an idea of how fast the black hole was spinning.

They focused their search on ASASSN-14li, the tidal disruption event that astronomers identified in November 2014, using the ground-based All-Sky Automated Survey for SuperNovae (ASASSN).

"This system is exciting because we think it's a poster child for tidal disruption flares," Pasham says. "This particular event seems to match many of the theoretical predictions."

The team looked through archived datasets from three observatories that collected X-ray measurements of the event since its discovery: the European Space Agency's XMM-Newton space observatory, and NASA's space-based Chandra and Swift observatories. Pasham previously developed a computer code to detect periodic patterns in astrophysical data, though not for tidal disruption events specifically. He decided to apply his code to the three datasets for ASASSN-14li, to see if any common periodic patterns would rise to the surface.

What he observed was a surprisingly strong, stable, and periodic burst of X-ray radiation that appeared to come from very close to the edge of the black hole. The signal pulsed every 131 seconds, over 450 days, and was extremely intense—about 40 percent above the black hole's average X-ray brightness.

"At first I didn't believe it because the signal was so strong," Pasham says. "But we saw it in all three telescopes. So in the end, the signal was real."

Based on the properties of the signal, and the mass and size of the black hole, the team estimated that the black hole is spinning at least at 50 percent the speed of light.

"That's not super fast—there are other black holes with spins estimated to be near 99 percent the speed of light," Pasham says. "But this is the first time we're able to use tidal disruption flares to constrain the spins of supermassive black holes."

Illuminating the invisible

Once Pasham discovered the periodic signal, it was up to the theorists on the team to find an explanation for what may have generated it. The team came up with various scenarios, but the one that seems the most likely to generate such a strong, regular X-ray flare involves not just a black hole shredding a passing star, but also a smaller type of star, known as a white dwarf, orbiting close to the black hole.

Such a white dwarf may have been circling the , at ISCO—the innermost stable circular orbit—for some time. Alone, it would not have been enough to emit any sort of detectable radiation. For all intents and purposes, the white dwarf would have been invisible to telescopes as it circled the relatively inactive, spinning black hole.

Sometime around Nov. 22, 2014, a second star passed close enough to the system that the black hole tore it apart in a tidal disruption flare that emitted an enormous amount of X-ray radiation, in the form of hot, shredded stellar material. As the black hole pulled this material inward, some of the stellar debris fell into the black hole, while some remained just outside, in the innermost stable orbit—the very same orbit in which the white dwarf circled. As the white dwarf came in contact with this hot stellar material, it likely dragged it along as a luminous overcoat of sorts, illuminating the white dwarf in an intense amount of X-rays each time it circled the black hole, every 131 seconds.

The scientists admit that such a scenario would be incredibly rare and would only last for several hundred years at most—a blink of an eye in cosmic scales. The chances of detecting such a scenario would be exceedingly slim.

"The problem with this scenario is that, if you have a black hole with a mass that's 1 million times that of the sun, and a white dwarf is circling it, then at some point over just a few hundred years, the white dwarf will plunge into the black hole," Pasham says. "We would've been extremely lucky to find such a system. But at least in terms of the properties of the system, this scenario seems to work."

The results' overarching significance is that they show it is possible to constrain the spin of a black hole, from tidal disruption events, according to Pasham. Going forward, he hopes to identify similar stable patterns in other star-shredding events, from black holes that reside further back in space and time.

"In the next decade, we hope to detect more of these events," Pasham says. "Estimating spins of several black holes from the beginning of time to now would be valuable in terms of estimating whether there is a relationship between the spin and the age of ."


Explore further

Researcher reports new information about black holes

More information: "A loud quasi-periodic oscillation after a star is disrupted by a massive black hole," Science (2019). dx.doi.org/10.1126/science.aar7480
Journal information: Science

Citation: X-ray pulse detected near event horizon as black hole devours star (2019, January 9) retrieved 21 May 2019 from https://phys.org/news/2019-01-x-ray-pulse-event-horizon-black.html
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Jan 09, 2019
This comment has been removed by a moderator.

Jan 09, 2019
Yet another artist's impression.

Jan 09, 2019
See, here's the thing: explain regular pulses of X-rays.

Astrophysicists can. You can't. Your "explanation" is goddidit. Weak. Contemptible. Logically unsound.

Jan 09, 2019
In search of black holes and dark matter astrophysicists are relying on indirect observations. It would seem that the measurement of the event horizon of a black hole directly would be a direct evidence. However, by the nature of a horizon, any real measurement of the event horizon will be indirect. The Event Horizon Telescope will get picture of the silhouette of the Sgr A* which is due to optical effects of spacetime outside of the event horizon. The result will be determined by the simple quality of the resulting image that does not depend on the properties of the spacetime within the image. So, it will be also indirect and an existence of BH is a hypothesis.
https://www.acade...ilky_Way

Jan 09, 2019
See, here's the thing: explain regular pulses of X-rays.

Astrophysicists can. You can't. Your "explanation" is goddidit. Weak. Contemptible. Logically unsound.

Explain it then. "Theoretical models of tidal disruption flares" seems to be these guys "explanation". Relaxation oscillator?

Jan 09, 2019
You missed it.

Remnants of a star disrupted by tidal forces spinning around the accretion disk.

Next time read the article.

Jan 09, 2019
"This particular event seems to match many of the theoretical predictions." "Once Pasham discovered the periodic signal, it was up to the theorists on the team to find an explanation for what may have generated it." That is far from an explanation. Eggs theories seem as plausible as any of this bias confirming pseudo-science. Relaxation oscillator is the explanation.

Jan 09, 2019
The theorists did. Which you'd know if you read the article.

Jan 10, 2019
They explained that an event that fits their computer model might have been observed. That is it. The original abstract is full of assumptions with very little or no experimental results.

Jan 10, 2019
Except for the 131 second signal which you seem to be trying to avoid. And don't have an explanation for.

They do.

Jan 10, 2019
Personally, I think the coincidence of a star being swallowed in just the right position (and time) to interact with an already present white dwarf, is much less likely than the core of the star being swallowed playing the role of a white dwarf. In other words, a star reaching the red giant stage could provide both the dense core and tenuous environment.

Also if a star orbiting the SMBH reached the life stage where it became a giant, then it's next perasterion (or whatever) could result in a new close-in orbit very quickly. (The part of the star sticking across the event horizon would effectively get ripped off. Since this wing of the star is travelling fastest wrt the SMBH, the mass stripped off would have the effect of reducing the star's net energy. So it would get pulled inward.

Jan 10, 2019
You think that signal is what they say they believe it might be? I'm the only one that does have an explanation. Any smart kid can build a relaxation oscillator. So of course Jeebus or Mother Nature can too. I'm not working with much data here so I could of course be wrong. And I'm not sure what has caused this circuit. Also, I have to admit an aversion to these stupendous events like an SMBH rotating at fifty percent the speed of light, which they mention is actually slow compared to most others they "observe", ripping apart stars and "eating" them. Though there probably is all kinds of fantastical stuff we can't even imagine going on right this second.

Jan 10, 2019
I ain't seen any explanation from you.

131 seconds is the orbital period of the remains of the star around the accretion disk.

Pretty obvious when you think about it.

Jan 11, 2019
Given the mansplanation of a black hole event horizon is that spherical coordinate radii of 'black holes' to that radial 'surface' of infinitessimal instantaneous thickness has an instantaneous negative gravitational escape velocity vector of the local speed of light with all points inside of that surface having necessary escape velocities greater than 'c'. That is the exacting definition of black holes that violates Einstein's so called speed limit which is really a 'terminal velocity' similar to that of Newtonian falling objects in non-empty mediums of non-zero kinematic or static viscosities.
Since 'c' is a variable with its value dependent on D'Arcy fluid friction of the transversed medium, with space which is never empty this value seeks what we call 'c' = 3 X (10^9)m/sec. Of course not only matter in the cold so called vacuum of space but also energy field found there and the zero point fields should be considered, 'C' might not be 'c' after all; and BH's maybe eggshells.

Jan 11, 2019
I ain't seen any explanation from you.

131 seconds is the orbital period of the remains of the star around the accretion disk.

Pretty obvious when you think about it.


They have practically nothing, just a very weak and very low probability conjecture and they freely admit that, you should read the article:

The scientists admit that such a scenario would be incredibly rare and would only last for several hundred years at most—a blink of an eye in cosmic scales. The chances of detecting such a scenario would be exceedingly slim.

"The problem with this scenario is that, if you have a black hole with a mass that's 1 million times that of the sun, and a white dwarf is circling it, then at some point over just a few hundred years, the white dwarf will plunge into the black hole," Pasham says. "We would've been extremely lucky to find such a system. But at least in terms of the properties of the system, this scenario seems to work.

Jan 12, 2019
Still waiting for an explanation of the 131 second pulse. So far, crickets.

Jan 12, 2019
Still waiting for an explanation of the 131 second pulse. So far, crickets.


This isn't US court. I don't have to prove this explanation wrong or provide another culprit, there could be many. You have to prove it correct. And matching it to computer simulations doesn't. Our, your and my, understanding of the fundamental structure of the universe is quite different, you with Quantum Mechanics and General and Special Relativity, and me with ether modalities. Not much common ground. I don't think either of us can convince the other of their kooky theories.

Jan 12, 2019
This isn't US court. I don't have to prove this explanation wrong r provide another culprit, there could be many. You have to prove it correct.


No! No! No! Mathematicians prove theorems correct. Scientists attempt to disprove theorems. Scientific theorems that have been tested many times are generally accepted as correct, but there is still a lot of money spent retesting settled science. I'm retired now, but with a degree in statistics I sometimes end up on both sides. (Proving the statistical methods used in a scientific experiment wrong--at least how they are being used there. Climate 'science' has a nasty habit of using normal theory statistics, when they should use order theory, or time series analysis. But that is a different battle.)

Here there is nothing in particular wrong with their analysis. However Bayes' theorem strongly argues for what they are observing to be the effect of one star falling into a black hole, not two.

Jan 12, 2019

No! No! No! Mathematicians prove theorems correct. Scientists attempt to disprove theorems. Scientific theorems that have been tested many times are generally accepted as correct, but there is still a lot of money spent retesting settled science. (Proving the statistical methods used in a scientific experiment wrong--at least how they are being used there. Climate 'science' has a nasty habit of using normal theory statistics, when they should use order theory, or time series analysis. But that is a different battle.)

Thanks for the post. Proper interpretation of the inputs and outputs of experiments "settle" science. Mathematics is not science. It is a tool used to interpret results and make models. It only works if the foundations of your knowledge lead to correct interpretations. They don't believe in the dialectric(ether) field. So their self confirming interpretations lack the foundations necessary for proper understanding.

Jan 12, 2019
So you don't have an explanation and they do.

We done here?

Jan 12, 2019
Let me put it this way: if you have no explanation you can articulate, and they do, you're correct, it's not a court of law. It's science. And an explanation that's internally and externally consistent always is better than no explanation at all. So if you got something bring it.

I'm not automatically opposed to aether hypotheses; in some ways GRT can be seen as an aether theory, though not the type of aether proposed in the 19th century. But I'd have to see what you're talking about first, without all the handwaving and politics.

Jan 12, 2019
See, here's the thing: the explanation is simple and obvious. A star has been disrupted by tidal forces and incorporated into the accretion disk, and its remnant is orbiting around the black hole at nearly the minimum radius. That means it shines in our direction every 131 seconds, and that accords with other measures of the black hole's mass and the predictions of GRT.

I don't necessarily agree with the whole white dwarf thing. I'd like to see more evidence of that, so I won't defend it. But the basic facts are pretty compelling.

Jan 14, 2019
Let me put it this way: if you have no explanation you can articulate, and they do, you're correct, it's not a court of law. It's science. And an explanation that's internally and externally consistent always is better than no explanation at all. So if you got something bring it.

I'm not automatically opposed to aether hypotheses; in some ways GRT can be seen as an aether theory, though not the type of aether proposed in the 19th century. But I'd have to see what you're talking about first, without all the handwaving and politics.

You are confusing "explanation" with observation. That is not good science. I blame you that I don't have a robot butler and a flying car yet.

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