The Milky Way Is Hiding Tens Of Thousands Of Black Holes
“This study is of tremendous importance, since it provides us with the first real evidence of what LISA will be looking for, further motivating us to look for these events that, as we now know, must exist. Unlike LIGO’s black holes, these inspiraling events will give us weeks, months, or even years of lead-up time, allowing us to pinpoint exactly where and when we’ll need to look to see these mergers coming. This is the first confirmation of the theory that tens of thousands of black holes ought to exist around supermassive ones at the centers of galaxies, and allows us to better predict how many gravitational wave events we’re likely to see coming from them.“
At the center of our Milky Way, our galaxy houses a supermassive black hole: Sagittarius A*. At four million solar masses, it’s the most massive object in our entire galaxy, while orbiting around it are stars, gas, dust, and many other astrophysical objects. This is a region where new star formation is rampant, and so, in theory, there ought to be many thousands of black holes within just a few light years of Sagittarius A*, some of which ought to be detectable through their emission of X-rays from binary companions. For nearly 20 years, such a detection was elusive, since the flares that occur when black holes absorb large amounts of matter are too rare. But now, using the full suite of archival data from the Chandra X-ray observatory, scientists have found the steady, low-level X-ray emission these systems give off, revealing a population of approximately 10,000 black holes within 3 light years of Sagittarius A*.