WASHINGTON – The center of our galaxy is full of black holes, something like a Times Square for extra strangely strange objects, astronomers discovered.
For decades, scientists theorized that circles in the center of galaxies, including ours, were many stellar black holes, collapsed giant stars where gravity is so strong that even light does not filter. But until now they had not seen evidence of them in the core of the Milky Way.
Astronomers studying ancient X-rays in detail have found signs of a dozen black holes in the inner circle of the Milky Way. And since most black holes can not even be seen that way, they estimate that there are probably thousands of them there. They estimate that it could be around 10,000, maybe more, according to a study in a recent issue of the journal Nature.
"There's a lot of action going on there," said study lead author Chuck Hailey, an astrophysicist at Columbia University. "The galactic center is a strange place, that's why people like to study it."
The stellar black holes add up, and essentially circulate, to the well-known supermassive black hole, called Sagittarius A, which is stationed at the center of the Milky Way.
In the rest of the massive Milky Way, scientists have only detected about five dozen black holes so far, Hailey said.
Newly discovered black holes are about 19.2 billion miles from the supermassive black hole in the center. So there's still a lot of empty space and gas in the middle of all those black holes. But if you take the equivalent space around the Earth, there will be no black holes, not thousands, Hailey said.
Earth is in a spiral arm about 3,000 light years away from the center of the galaxy. (One light year is 5.9 trillion miles.)
Harvard astronomer Avi Loeb, who was not part of the study, praised the finding as exciting, but confirming what scientists had been waiting for a long time.
The newly confirmed black holes are approximately 10 times the mass of our sun, unlike the central supermassive black hole, which has a mass of 4 million suns. In addition, those detected are only of the type that are binary, where a black hole has been associated with another star and together they emit a large amount of X-rays as the outer layer of the star is absorbed by the black hole. Those X-rays are what astronomers observe.
When astronomers observe closer binary black hole systems, they can see the relationship between what is visible and what is too weak to be observed from afar. Using that proportion, Hailey calculates that, although they only detected a dozen, there must be 300 to 500 binary black hole systems.
But binary black hole systems are probably only 5 percent of all black holes, so that means there are actually thousands of them, Hailey said.
There are good reasons why black holes in the Milky Way tend to be at the center of the galaxy, Hailey said. First, its mass tends to take them to the center. But mainly the center of the galaxy is the perfect "hot house" for the formation of black holes, with a lot of dust and gas.
Hailey said that it is "something like a small farm where you have all the right conditions to produce and hold on to a lot of black holes."