Black hole discovery astonishes astronomers

Stephen Withers
Thursday, 04 January 2007 05:27

Science - Space

The early discovery of a black hole inside a globular star cluster by a team using the European Space Agency's XMM-Newton satellite has astonished astronomers.

Team leader Tom Maccarone of the University of Southampton said "We were preparing for a long, systematic search of thousands of globular clusters with the hope of finding just one black hole," but success came with the second cluster examined: NGC 4472, which is about fifty million light-years away in the Virgo Cluster.

Scientists had doubted that black holes could still exist in globular clusters as they are some of the oldest structures in the universe (over 12 thousand million years old), and so gravitational forces would have ejected any black holes thousands of million years ago.

One possibility is that the international team has discovered a intermediate mass black hole, larger than the relatively common stellar-sized black holes yet smaller than the supermassive black holes found at the centre of most galaxies.

"If a black hole is massive enough [around 100 times the mass of our sun], there's a good chance it can survive the pressures of living in a globular cluster, since it will be too heavy to be kicked out," said Arunav Kundu of Michigan State University, a co-author of the report. If

Another possibility is that the apparent X-ray brightness of the black hole is not due to its size, but a result of the radiation being reflected in our direction by surrounding gas. X-rays are emitted when gas falls into a black hole.