By Belinda McCallum | The Epoch Times
A pair of black holes found at the heart of a globular cluster is causing astronomers to rethink the idea that these dense bundles of stars should have only one black hole at their center.
Messier 22 (M22) is about 10,600 light-years away from Earth, and contains hundreds of thousands of stars tightly bound by gravity.
Using the Karl G. Jansky Very Large Array (VLA) in New Mexico, the astronomers studied M22 in search of an intermediate-mass black hole, which is smaller than the supermassive black holes found in galaxies’ centers, but larger than black holes that are several times the sun’s mass.
Instead, the team found two smaller black holes about 10 to 20 times heavier than the sun. These stellar-mass black holes are probably two of many formed from massive stars that exploded as supernovae early on during M22′s 12-billion-year-long life.
“Simulations of how globular clusters evolve show many black holes are created early in a cluster’s history,” said study co-author James Miller-Jones at the Curtin University, Australia, in a press release.
“The many black holes then sink towards the middle of the cluster where they begin a chaotic dance leading to most being thrown out of the cluster until only one surviving black hole remains.”
There are various explanations as to why there are multiple black holes, for example the cluster may not have contracted as much as believed, or the black holes may have reduced the core’s density and thus slowed their ejection rate.
“M22 may contain as many as 100 black holes but we can’t detect them unless they’re actively feeding on nearby stars,” Miller-Jones concluded. “We plan to do further study to pin down the properties of the two we’ve already found.” The research was published in Nature on Oct. 4.
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