Physicists used to think of them are being more solitary

Oct 4, 2012 14:10 GMT  ·  By

A finding made during a recent investigation calls into question past wisdom on the nature of interactions that develop between black holes. In the study, experts found that the dark behemoths could live in pairs and groups.

Furthermore, such pairs were discovered inside star clusters within our own galaxy, the Milky Way. According to investigators at the Michigan State University (MSU), in East Lansing, the new data may change our understanding of how these objects evolve over prolonged periods of time, Space reports.

Black holes are objects of infinite density, and come in the form of a point in space called a singularity, which is surrounded by an area called the event horizon. This represents the minimum distance an object can come to a black hole without becoming unable to escape its gravitational influence.

They are extremely heavy, and can contain anywhere from millions to several billion times the mass of our Sun. All of this matter is condensed in an area of space significantly smaller than the Moon.

“Before this work, there were zero black holes known in Milky Way globular clusters, so even finding one would have been exciting,” MSU astronomer and lead study author, Jay Strader, explains.

The fact that small, solar-mass black holes can form within star clusters has been known for quite some time. But astronomers didn't think it possible for two or more dark behemoths to develop inside the same cluster.

Gravitational and tidal interactions between them would lead to either one or more being expelled from the stellar cluster, or in a series of mergers, resulting in the formation of a supermassive black hole.

But a study of M22, a large globular cluster located about 10,600 light-years away, in the constellation Sagittarius, revealed the existence of a black hole pair among more than a million stars.

“{Contrary to our previous thoughts, globular clusters might be one of the best places to look for black holes, rather than one of the worst. We estimate that a population of five to 100 black holes may exist in the [M22] cluster,” Strader explains.

The dense objects were discovered using the Karl G. Jansky Very Large Array (VLA), in New Mexico, which surveys the sky at radio wavelengths. Details of the study appear in the October 4 issue of the top scientific journal Nature.

“We hypothesize that the reason our sources haven't been seen in previous X-ray searches is that they aren't accreting very much matter at all, so they don't produce the hot accretion disks that glow in the optical and X-rays,” Strader argues.

“If this is true, it suggests that radio observations could be a good way to find the quieter accreting stellar-mass black holes in our galaxy,” he concludes.