“Boring” Star Cluster Found To Host Hundreds Of Black Holes

Hubble image of the core of NGC 6101. NASA/ESA/HST

Astronomers have discovered that a well-known cluster of stars hosts hundreds of stellar black holes, going against the accepted framework for these objects.

NGC 6101 is at first glace a mundane globular cluster, a spherical collection of stars orbiting 36,000 light-years from the core of the Milky Way. Recently though, researchers noticed that it appeared to have some weird characteristics, being larger and more dynamically active than expected, so a team from the University of Surrey produced a computer simulation of the cluster to understand what was going on.

The results, published in the Monthly Notices of the Royal Astronomical Society, were quite surprising. The globular cluster is full of hundreds of blacks holes, formed over the 13 billion years of its life. Stellar black holes are formed after a star goes supernova, but such an event was believed to be dramatic enough to kick them out of a globular cluster. This finding shows that globular clusters can, in fact, hold onto their black holes.

“This research is exciting as we were able to theoretically observe the spectacle of an entire population of black holes using computer simulations,” said lead author Miklos Peter in a statement.

“The results show that globular clusters like NGC 6101, which were always considered boring are in fact the most interesting ones, possibly each harboring hundreds of black holes. This will help us find more black holes in other globular clusters in the universe.”

This research could help explain how the supermassive black holes at the center of galaxies form. If globular clusters are capable of trapping a large number of black holes, over time they could lead to mergers of these stellar black holes.

“Our work is intended to help answer fundamental questions related to dynamics of stars and black holes, and the recently observed gravitational waves. These are emitted when two black holes merge, and if our interpretation is right, the cores of some globular clusters may be where black hole mergers take place,” added co-author Professor Mark Gieles.


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