Studying black holes is complicated, namely because you can’t see them. And according to a recent study, we might have been missing a huge number of them.
In a paper, soon to be published in the Astrophysical Journal, astronomers discuss the discovery of a star orbiting a quiet black hole 7,200 light-years from Earth. Since this study looked at a tiny portion of the sky, it implies that there might be a large undiscovered population of these quiet black holes.
Until the recent discovery of gravitational waves, we could only discover their properties indirectly by looking at how they interact with other objects. The object, called VLA J2130+12, is very bright in radio waves, but it doesn’t emit many X-rays – which are one important signature in black hole binaries.
"Usually, we find black holes when they are pulling in lots of material. Before falling into the black hole this material gets very hot and emits brightly in X-rays," said Bailey Tetarenko of the University of Alberta, Canada, who led the study, in a statement. "This one is so quiet that it's practically a stealth black hole."
VLA J2130+12 is believed to be a few solar masses, with the companion star being significantly smaller, between 10 and 20 percent of our Sun. By combining radio observations from the Very Large Array and X-ray data from NASA’s Chandra Observatory, they concluded that the object must be a local, quiet black hole.
The other important finding in this study is that these objects might be incredibly common. The researchers estimate that tens of thousands to millions of black holes are hiding in the Milky Way.
"Unless we were incredibly lucky to find one source like this in a small patch of the sky, there must be many more of these black hole binaries in our galaxy than we used to think," said co-author Arash Bahramian, also of the University of Alberta.
Finding this population is not going to be easy, but if confirmed, it will help us understand what forces were at play during the infancy of our galaxy.