Astronomers at Columbia University in New York have discovered a galaxy of several thousand ordinary black holes surrounding the supermassive black hole Sagittarius A *, located in the center of our galaxy. The scientists note that observing these objects will help test Einstein's theory of relativity. The researchers shared their work in an article in the journal Nature.
“In all other parts of the galaxy, we have managed to discover only five hundred black holes. At the same time, the theory says that in a small region in the center of the Milky Way, whose length, width and height are only six light years, there are at least 10 thousand such objects. Only now do we have the first evidence to support this assumption,”commented Chuck Haley of Columbia University in New York.
As with presumably all galaxies, there is a very large black hole at the center of our Milky Way. In our case, it is called Sagittarius A *, its mass is about 4 million times heavier than our Sun and is located 26 thousand light years from Earth.
Scientists note that there are several dozen stars around Sagittarius A *, as well as several large gas clouds rotating around it at a very high speed. When these objects come too close to the black hole, then its gravity literally begins to tear them apart, which is accompanied by a very bright emission of radiation.
However, other black holes in the vicinity of Sagittarius A * will have a different fate, Hayley notes. In their case, the supermassive black hole constantly attracts them until they eventually merge with it. In this case, no flares in the optical range occur, and we can observe all the signs of this merger by bursts of gravitational waves invisible to us. It is for this reason that scientists could not find out the presence of black holes in the center of our galaxy and, accordingly, check the correctness of the prediction of their number by the theory describing the evolution of galaxies.
A team of American astrophysicists was able to obtain the first evidence that these black holes actually exist. And not only to prove their presence, but also to count their number. Scientists have suggested that some of these black holes will revolve around the center of the Milky Way, not alone, but paired with an ordinary star, pulsar or some other visible object.
In the presence of such a pair, black holes, as a rule, act as dominants and gradually begin to steal matter from a less dense and larger star. If the volume of gas and dust extracted from such a star becomes too large, then the black hole simply does not have time to suck in all the matter, as a result of which a kind of "donut" of hot gas and dust appears in its vicinity, inside which X-ray flashes periodically appear.
Astrophysicists explain that these beams of light have a relatively low brightness compared to other stellar cataclysms, but they occur much more often and have a peculiar spectrum. This is precisely what makes it possible to distinguish them from other objects in the center of our galaxy.
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As a field for research, Haley's team used images of the vicinity of the Sagittarius A * black hole, obtained using the Chandra X-ray observatory over the past ten years. On them, scientists tried to find the above-described pairs of black holes and ordinary stellar objects.
As a result, the researchers discovered 12 such pairs at once, located at a small (in cosmic terms, of course) distance from the main black hole of our galaxy. According to astrophysicists, half of these pairs may consist of black holes and pulsars. At the same time, their location and properties indicate that about five hundred similar pairs and about 10 thousand single black holes revolve around Sagittarius A *.
The central black hole of the Milky Way (marked with a green circle) is surrounded by many X-ray sources (marked with blue and red circles), which are pairs of black holes and stars.
“We were able to confirm one of the key astronomical theories, and make significant progress in testing many other ideas. For example, this discovery will help us observe gravitational waves more efficiently, as we now have the ability to accurately estimate how many black hole mergers can occur in the Milky Way. It turns out that everything we need can be found in the center of our Galaxy,”added Haley.
Nikolay Khizhnyak