Research: The pulse structure suggests that the remote black hole should rotate at least 50% of the speed of light –

Now, researchers at MIT and other countries have studied data from several telescopes and have discovered a curiously intense, stable and periodic X-ray pulse or signal in all datasets. The signal appears to come from an area very close to the black hole event horizon – the point beyond which the material is inevitably swallowed by the black hole. The signal seems to brighten and weaken periodically every 131 seconds and persists for at least 450 days.

The researchers believe that anything that emits the periodic signal must orbit around the black hole, just outside the event horizon, near stable stable circular orbit, or ISCO, the smallest orbit on which a particle can move securely around a black hole.

Given the stable proximity of the signal to the black hole and the mbad of the black hole, which researchers previously estimated about 1 million times greater than that of the sun, the team calculated that the black hole was about 50% the speed of light.

The results, published today in the newspaper Science, are the first demonstration of a tidal disturbance flare used to estimate the rotation of a black hole.

The first author of the study, Dheeraj Pasham, a postdoc at the Kavli Institute for Research in Astrophysics and Space Research at MIT, said that most supermbadive black holes are dormant and generally do not release much It is only from time to time that they release intense activity, for example when the stars get close enough for the black holes to devour them. Now, he says, considering the team's findings, such tidal flares can be used to estimate the spin of supermbadive black holes – a feature so far incredibly tricky to pin down.

"Events in which black holes are shredding too close stars could help us map the rotations of several supermbadive black holes that are dormant and hidden in the center of the galaxies," says Pasham. "It could help us understand how galaxies have evolved over cosmic time."

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

A real signal

Theoretical models of tidal disturbance eruptions show that when a black hole tears a star, some of that star's material may remain out of the event horizon, turning at least temporarily into an orbit stable as ISCO and emitting periodic flashes. X-rays before finally being powered by the black hole. The periodicity of the X-ray flashes therefore encodes essential information on the size of the CITP, itself dictated by the speed of rotation of the black hole.

Pasham and his colleagues thought that if they could see such regular bursts close to a black hole that had just been disturbed by the tides, these signals could give them an idea of ​​how fast the black hole was turning.

They focused their research on ASASSN-14li, the tidal disturbance event identified by astronomers in November 2014, using the All-Sky Ground Survey for SuperNovae (ASASSN).

"This system is exciting because we think it is a very good start for tidal disturbance eruptions," says Pasham. "This particular event seems to correspond to many theoretical predictions."

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

What he observed was a surprisingly strong, stable and periodic X-ray explosion, which seemed to come very close to the edge of the black hole. The pulsed signal every 131 seconds, for more than 450 days, was extremely intense – about 40% above the average X-ray brightness of the black hole.

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

Based on the signal properties, mbad and size of the black hole, the team estimated that the black hole turned at least 50% of the speed of light.

"It's not very fast. There are other black holes whose rotational speed is estimated at nearly 99% that of light, "says Pasham. "But this is the first time we are able to use tidal flares to limit supermbadive black hole spins."

Illuminate the invisible

Once Pasham discovered the periodic signal, it was up to the team theorists to find an explanation for what had eventually generated it. The team has proposed various scenarios, but the one that seems most likely to generate such a powerful and regular radiographic eruption does not just involve a black hole shredding a pbading star, but also a smaller type of star, called a star. white. dwarf, gravitating around the black hole.

Such a white dwarf may have encircled the supermbadive black hole, at the most internal and stable circular ISCO – orbit – for a while. Alone, it would not have been enough to emit any detectable radiation. For all practical purposes, the white dwarf would have been invisible to telescopes as he surrounded the rotating, relatively inactive black hole.

On or about November 22, 2014, a second star pbaded close enough to the system that the black hole tore it into a tidal flare that emitted a tremendous amount of X-rays in the form of hot, shredded star material. When the black hole pulled this material inward, some stellar debris fell into the black hole, while others remained just outside, in the most stable internal orbit – the same orbit in which the white dwarf has turned. When the white dwarf came into contact with this hot stellar material, it probably resulted in a bright coat, illuminating the white dwarf with an intense amount of X-rays each time he was circling the black hole, every 131 seconds.

Scientists admit that such a scenario would be extremely rare and would last only several hundred years at most – a wink at the cosmic scale. The chances of detecting such a scenario would be extremely slim.

"The problem with this scenario is that, if you have a black hole with a mbad that is 1 million times greater than the sun's and a white dwarf bypbades it, then, at some point, over a few hundred only years ago, the white dwarf plunged into the black hole, "Pasham says," We would have been extremely lucky to find such a system, but at least as far as the properties of the system are concerned, this scenario seems to be working. "

The primary importance of the results is that they show that it is possible to limit the rotation of a black hole from disturbances due to tides, according to Pasham. In the future, he hopes to identify similar stable patterns in other star destruction events, from black holes located further back in time and space.

"Over the next ten years, we hope to detect more such events," says Pasham. "It would be useful to estimate the rotations of several black holes from the beginning up to now to determine whether or not there is a relationship between the rotation and the age of the black holes."

This research was funded in part by NASA.