The center of our galaxy has an abundance of black holes, according to a recent discovery made by a group of astronomers.
For decades, scientists have theorized that, at the center of galaxies, including our own, there were numerous black holes, giant collapsed stars in which gravity is so strong that not even light can escape. But they were not able to detect the evidence of it in the core of the Milky Way until now.
Astronomers who examined older observations made with x-rays have found evidence of a dozen black holes in the inner circle of the galaxy. And since most black holes can not be detected even in that way, scientists estimate that there are probably thousands of them there. They estimate that it could be about 10,000, maybe more, according to a study published Wednesday in the journal Nature.
“There’s a lot of action there,” said the study’s lead author, Chuck Hailey, an astrophysicist at Columbia University. “The galactic center is a strange place, which is why people like to study it.”
The stellar black holes are additional and essentially revolve around the already known supermassive black hole, called Sagittarius A*, which is fixed at the center of the Milky Way.
In the rest of the massive galaxy, scientists have only detected about five dozen black holes so far, Hailey said.
The newly discovered black holes are about 19.2 trillion miles from the supermassive black hole in the center. So there is still a lot of empty space and gas between those black holes. For reference, the Earth is in a spiral arm about 3,000 light years from the center of the galaxy. (One light year equals 5.9 trillion miles).
The discovered black holes are about 10 times the mass of our sun, small when compared to the supermassive black hole in the center of the galaxy, which has a mass of four million suns. The confirmed black holes, moreover, are of the binary type, in which one of them has joined another star and together they emit large quantities of x-rays as the black hole absorbs the outer layer of the star. Those x-rays are what scientists detect.
When astronomers examine closer the binary black holes, they were able to determine the ratio between what is visible and what is too faint to be observed from afar. Using that rate, Hailey calculates that even if only a dozen have been detected, there must be between 300 and 500 of those binary systems.
But binary black holes are probably just 5% of all black holes, and that means there really are thousands of them, Hailey said.
There are good reasons why black holes in the Milky Way tend to be in the center of the galaxy. First, they tend to move toward the center due to their mass. But mainly because the center of the galaxy is a perfect “greenhouse” for the formation of black holes, with lots of dust and gases.
According to the researchers, it is “like a small farm where you have all the conditions to produce and retain a lot of black holes.”