“Exceptional find”: how the light of a dying star helped to calculate the speed of rotation of a black hole
American scientists measured the mass and for the first time calculated the speed of rotation of a supermassive black hole in the center of a galaxy far removed from the Earth. The mass of a space object can be from 100 thousand to 10 million masses of the Sun, its diameter is 300 times greater than that of the Earth, and the rotation speed is more than 50% of the speed of light in a vacuum.
Differential gravitational forces near massive black holes can break objects trapped in their field. Stars in this regard are no exception. In this case, the remnants of a "torn" star will spiral along the event horizon, emitting light, including in the X-ray range. This is the radiation American scientists observed in the course of a new study. As a result, for the echoes of a dying star, astrophysicists for the first time managed to calculate the speed of rotation of a black hole.
Experts observed a supermassive black hole located in the center of a galaxy, 290 million light-years distant from us. In November 2014, optical telescopes registered a powerful flash of light near this giant object. In a more detailed study, scientists found that a flash appeared immediately after the tidal forces of a supermassive black hole “to pieces” tore a star that had fallen into their field.
After this, astrophysicists observed how the "fragments" of a dying star spiral along toward the event horizon. At the same time, using the NASA Chandra X-ray Observatory and two other space telescopes, specialists investigated the properties of X-rays emanating from the "fragments" of the former star.
It should be noted that since black holes themselves do not emit light or any energy, the only way to measure their rotational speed is to observe other objects rotating around them, and then adjust the results of these observations so that they can calculate the rotational speed. black holes themselves.
In the course of research, scientists managed to establish that a black hole is at least several hundred thousand times heavier than the Sun, and its diameter is 300 times larger than the Earth's. X-rays from the fragments of the star fell into the field of view of telescopes every 131 seconds. So lasted 450 days. In total, experts managed to register more than 300 thousand "flashes" of light - so many times the remnants of a star made a revolution in the orbit of a space giant. By combining this data with information about the mass and size of a black hole, astronomers found out that it must rotate very quickly - at a speed of more than half the speed of light in a vacuum.
Scientists have previously tried to use X-ray data to measure the speed of rotation of a black hole. However, similar observations were made for objects that are only several times more massive than the Sun. In addition, astronomers were able to register only a few periods of rotation of stellar "fragments" around the black hole, which reduced the reliability of the information obtained.
“This is an exceptional find. Never before have scientists been able to observe such a bright signal in the vicinity of a black hole, which has not disappeared from telescopes' field of view for such a long period of time, ”said study author Alessia Franchini.
In the future, astrophysicists expect to detect with the help of telescopes new similar phenomena, in order to better understand how stars interact with black holes.