Thousands of Black Holes Found Clustered at Center of 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.

For years, scientists have known that a monster black hole sits in the middle of the galaxy. Called Sagittarius A* (Sgr A*), the compact object is more than four million times as massive as our sun, but it’s packed into a region of space no bigger than the distance between Earth and the sun.

Scientists had long suspected that as many as 20,000 smaller black holes were orbiting the galactic center. But as the name suggests, black holes are not easy to see directly.

To overcome this obstacle, a team of astronomers went looking for stellar binaries—specifically ones with black holes that are paired closely with stars. In these cases, matter from the star falls into its ultradense partner, and the swirling gas forms what’s known as an accretion disk around the black hole’s maw. This superheated disk of gas emits x-rays that astronomers can detect.

“They’re just the tip of the iceberg,” says Chuck Hailey, an astrophysicist at the Columbia Astrophysics Lab and lead author of the study, published today in the journal Nature. “But the only way we could find these black holes is to look for these tracers.”

Thousands More?
The team then went looking for black hole binaries that are within about three light-years of Sgr A* and that are moving in ways that suggest they are falling into their supermassive cousin.

“Over a long period of time, you’d expect these black holes to rain down onto the supermassive black hole, where they get caught into orbit,” Hailey says.

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SOURCE: National Geographic, Sarah Gibbens