Michael Muno of the University of California at Los Angeles and his colleagues analyzed data collected by NASA's Chandra X-ray Observatory as the instrument monitored the region around Sgr A*. The team sifted through data from all the x-ray sources situated within 70 light-years of Sgr A*, searching for those that had characteristics of black holes and neutron stars in binary systems and found four sources within just three light-years of the central black hole. Initial models had suggested there was less than a one-in-five chance that even one such binary would be so close to Sgr A*. "The observed high concentration of these sources implies that a huge number of black holes and neutron stars have gathered in the center of the galaxy," Muno says. Indeed, the team estimates that up to 10,000 or more stellar-mass black holes and neutron stars could be swarming around Sgr A*.
The findings are the first evidence to date of a dense stellar graveyard that has been theorized for years and indicate that the black holes and neutron stars will slowly be swallowed up by Sgr A* at a rate of about one every million years, leaving the central supermassive black hole about 3 percent more massive in a few billion years. A detailed report describing the results has been submitted to Astrophysical Journal Letters.