New type of black hole discovered

A new class of black hole, more than 500 times the mass of the Sun, has been discovered.

Until now, identified black holes have been either super-massive - several million to several billion times the mass of the Sun - in the centre of galaxies, or about the size of a typical star, at between three and 20 solar masses.

It has been long believed by astrophysicists that there might be a third, intermediate class of black holes, with masses between a hundred and several hundred thousand times that of the Sun. However, such black holes have not been reliably detected until now.

The new discovery, in a galaxy approximately 290 million light years from Earth, is the first solid evidence of a new class of medium-sized black holes. The team, led by astrophysicists at the Centre d'Etude Spatiale des Rayonnements in France, detected the new black hole with the European Space Agency's XMM-Newton X-ray space telescope.

"While it is widely accepted that stellar mass black holes are created during the death throes of massive stars, it is still unknown how super-massive black holes are formed," says the lead author of the paper, Dr Sean Farrell, now based at the Department of Physics and Astronomy at the University of Leicester.

He added: "One theory is that super-massive black holes may be formed by the merger of a number of intermediate mass black holes. To ratify such a theory, however, you must first prove the existence of intermediate black holes. This is the best detection to date of such long sought after intermediate mass black holes."

The new source, dubbed HLX-1 (Hyper-Luminous X-ray source 1), lies towards the edge of the galaxy ESO 243-49. It is ultra-luminous in X-rays, with a maximum X-ray brightness of approximately 260 million times that of the Sun.

The X-ray signature of HLX-1 and the lack of a counterpart in optical images confirm that it is neither a foreground star nor a background galaxy, and its position indicates that it's not the central engine of the host galaxy. A variation in its X-ray signature indicates that it must be a single object. The huge radiance observed can only be explained, say the researchers, if HLX-1 contains a black hole more than 500 times the mass of the Sun.

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