Chuck Hailey from Columbia University and colleagues teased out the faint signal of a dozen "black hole binaries" — where a black hole and another object, such as a star, orbit each other — close to their supermassive counterpart in the centre of the Milky Way. WASHINGTON (Reuters) - Black holes are hanging out at the center of our galaxy by the thousands, according to scientists who have detected a bunch of them in the neighborhood of a supermassive black hole already known to reside at the heart of the Milky Way. A gaggle of black holes has been found clustered around the center of our home galaxy, the Milky Way—and the discovery hints at a much larger population of black holes hidden across the galaxy. “Everything you’d ever want to learn about the way big black holes interact with little black holes, you can learn by studying this distribution,” said Columbia Astrophysicist Chuck Hailey, co-director of the Columbia Astrophysics Lab and lead author on the study. For more than two decades, researchers have searched unsuccessfully for evidence to support a theory that thousands of black holes surround supermassive black holes (SMBHs) at the center of large galaxies. “We’re actually missing most of them just because the center of the galaxy is so far away.” The new detection makes Hailey wonder just how many of these black holes are floating around without a star companion, completely invisible to our telescopes. If we could find black holes that are coupled with low mass stars and we know what fraction of black holes will mate with low mass stars, we could scientifically infer the population of isolated black holes out there.”

Based on the data from Chandra X-ray Observatory, the team tested the technique and searched for X-ray signatures indicating the fusion between a black hole and a low mass binary in an inactive state. “There are only about five dozen known black holes in the entire galaxy — 100,000 light years wide — and there are supposed to be 10,000 to 20,000 of these things in a region just six light years wide that no one has been able to find,” Hailey said, adding that extensive fruitless searches have been made for black holes around Sgr A*, the closest SMBH to Earth and therefore the easiest to study.
A study published to the journal Nature finds dozens of potential stellar mass black holes in the Galactic Center, suggesting there may be as many as 20,000 orbiting the supermassive black hole Sagittarius A*.