Star Cluster Holds Midweight Black Hole, VLA Indicates

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The Very Large Array CREDIT: NRAO/AUI/NSF

Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have greatly strengthened the case that supermassive black holes at the cores of galaxies may have formed through mergers of smaller black holes. Their VLA studies showed that a globular star cluster in the galaxy M31 probably has a black hole with 20,000 times the mass of the Sun at its core.

"That amount of mass is midway between the black holes left when giant stars explode as supernovae and the supermassive black holes with millions of times the mass of the Sun. It suggests that there is a clear path for forming the supermassive ones through successive mergers of smaller black holes," said James Ulvestad, of the National Radio Astronomy Observatory. Ulvestad, Jenny Greene of Princeton University, and Luis Ho of the Observatories of the Carnegie Institute of Washington presented their findings to the American Astronomical Society's meeting in Honolulu, Hawaii.

Black holes appear to be intimately connected with the formation of massive spherical bulges in galaxies. Astronomers have found a direct relationship between the mass of the black hole in such a galaxy and the mass of its central bulge. However, it is unclear whether small galaxies contain smaller black holes, and their discovery may lead to new insights about the impact of black holes on galaxy formation. As Greene stated, "In recent years, we have been detecting black holes with masses between 100,000 and a few million times the mass of the Sun, but less massive objects have been exceptionally difficult to find."

Read more: Physorg.com