Sagittarius A* swarm: Black hole bounty captured in the Milky Way center

Astronomers have discovered evidence for thousands of black holes located near the center of our Milky Way galaxy using data from NASA's Chandra X-ray Observatory.

This black hole bounty consists of stellar-mass black holes, which typically weigh between five to 30 times the mass of the Sun. These newly identified black holes were found within three light years—a relatively short distance on cosmic scales—of the supermassive black hole at our Galaxy's center known as Sagittarius A* (Sgr A*).

Theoretical studies of the dynamics of stars in galaxies have indicated that a large population of stellar mass black holes—as many as 20,000—could drift inward over the eons and collect around Sgr A*. This recent analysis using Chandra data is the first observational evidence for such a black hole bounty.

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Credit: NASA/CXC/Columbia Univ./C. Hailey et al.

A black hole by itself is invisible. However, a black hole—or neutron star—locked in close orbit with a star will pull gas from its companion (astronomers call these systems "X-ray binaries"). This material falls into a disk and heats up to millions of degrees and produces X-rays before disappearing into the black hole. Some of these X-ray binaries appear as point-like sources in the Chandra image.

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At the hearts of most, if not all, galaxies are supermassive black holes with masses that are millions to billions of times that of the sun.

For example, at the center of our galaxy, the Milky Way, lies Sagittarius A*, which is about 4.5 million solar masses in size.

However, until now, researchers failed to detect such a heavy concentration of black holes, called a "density cusp." "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.'