A recent study suggests that the center of the Milky Way is hiding about ten thousand black holes. But we have never previously been able to see them.

For decades astronomers have suspected there might be a host of smaller black holes. All of them surrounding the supermassive one, Sagittarius A*, that sits at the center of our Milky Way. But it’s so hard to see them and so astronomers haven’t been able to prove the theory.

“This is just kind of astonishing that you could have a prediction for such a large number of objects and not find any evidence for them,” says US astrophysicist Dr. Chuck Hailey, from Columbia University in New York City.

So, now scientists have been able to spot the traces sent out by the smaller black holes.

The Discovery

Scientists searched for X-rays emitted by a subgroup of low-mass black holes that have captured a passing star in their gravitational grip, creating a “black hole binary”.  So, they discovered a dozen such X-ray binaries within about one parsec, or about 3.26 light-years, from the galactic core. Scientists detected them using data from NASA’s Chandra X-ray Observatory

They detailed their findings in the April 5 issue of the journal Nature.

Their calculations show that there must be several hundred more black holes paired with stars in the galactic center. Also, about 10,000 isolated black holes.

“This finding confirms a major theory and the implications are many,” said Dr. Hailey.

“It is going to significantly advance gravitational wave research because knowing the number of black holes in the center of a typical galaxy can help in better predicting how many gravitational wave events may be associated with them,” he added. “All the information astrophysicists need is at the center of the galaxy.”

A halo of gas and dust surrounds Sagittarius A* that provides the perfect breeding ground for massive stars, which can then give rise to black holes after they die, said study lead author Chuck Hailey.

“The Milky Way is really the only galaxy we have where we can study how supermassive black holes interact with little ones because we simply can’t see their interactions in other galaxies,” Hailey said in a statement. “In a sense, this is the only laboratory we have to study this phenomenon.”

Researchers report their findings in the latest issue of Nature journal.

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Thumbnail image: Center of the Milky Way galaxy seen from New Zeland. Credit: Dave Young