There could be hundreds, if not thousands, of stellar black holes in the center of our galaxy. According to a recent survey conducted in the galactic bulge, they would orbit the supermassive black hole of the Milky Way.
In the 1970s, astronomers had already realized that a supermassive black hole was at the center of our galaxy. Located about 26 000 light years from Earth between the constellations of Sagittarius and Scorpio, this black hole (Sagittarius A *) is 44 million kilometers in diameter. It is also about 4 million times more massive than our Sun, exerting a gigantic gravitational pull. But it would not be alone, according to a recent poll conducted by NASA’s Chandra X-ray Observatory. Astronomers have discovered evidence of hundreds — if not thousands — of black holes near the center of the Milky Way.
Black holes are not detectable in visible light. However, objects stuck in binaries (with another object) will eject the material from their companions. This matter heated to millions of degrees will then be visible as X-rays which can then be detected. Using Chandra’s data, the researchers searched for X-rays from sources about 12 light-years away from Sgr A *. They then selected these sources with X-ray spectra similar to known X-ray binaries, which emit relatively large amounts of low-energy X-rays. Using this method, they detected fourteen x-ray binaries located within three light-years of Sgr A *, all of which contained stellar mass black holes — between 5 and 30 times the mass of our Sun.
Since only the brightest X binaries containing black holes are likely to be detectable around Sgr A * (given the distance from the Earth), the researchers believe that this detection implies the existence of a population much bigger. According to their estimates, there could be at least 300 and up to a thousand stellar black holes around Sgr A *.
These results confirm what theoretical studies on star dynamics in galaxies have indicated in the past. According to them, a large population of stellar black holes (up to 20,000) could gather around a supermassive black hole in a galaxy. Here, however, it is the first observational evidence of black holes gathering near Sgr A *.
This study is also important in the recent field of research on gravitational waves. For example, knowing how many black holes are at the center of the galaxies – which will periodically merge with one another – astronomers will be able to better predict how many gravitational waves are associated with them.