Stellar mass black holes have been discovered, and astronomers now believe that supermassive black holes exist at the centres of most galaxies. But now a black hole has been discovered inside a globular star cluster. This could be one of the elusive “intermediate-mass” black holes.
Globular clusters contain thousands, or even millions of stars, and astronomers never thought they could hold a black hole. Computer simulations predicted that a black hole that formed in the cluster would sink into the centre of the cluster, but then inevitably get slung out into space after gravitational interaction with the stars in the cluster.
This new black hole was found by ESA’s XMM-Newton X-ray observatory, which was able to spot the tell-tale X-ray signature of a black hole. Well, the black hole itself is dark, but superheated matter surrounding the black hole gives off a tremendous amount of energy before it’s swallowed up.
The black hole is located inside a globular cluster in the relatively nearby elliptical galaxy NGC 4472, located about 50 million light-years away in the Virgo Cluster.
It’s possible that it gained mass by merging with other black holes, and consuming enough material that it could lock its position inside the middle of the galaxy, sort of like a mini-supermassive black hole. With enough mass, the stars in the cluster just wouldn’t able to eject it.