Planetary scientists have found the first solid evidence for a moderate-size black hole in a distant galaxy, backing up the idea that smaller black holes merge into huge ones.

A black hole is an object with such a powerful gravitational field that it absorbs all the light that passes near it and reflects nothing.

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 (between three and 20 Solar masses).

Now, an international team has discovered the black hole HLX-1, 290 million light years from Earth, which it is more than 500 times the mass of the Sun, using the European Space Agency's telescope, the 'Nature' journal reported.

Team member Dr Sean Farrell of the University of Leicester said: "While it is widely accepted that stellar mass black holes are created during death throes of massive stars, it is still unknown how super-massive black holes are formed.

"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.

"The identification of HLX-1 is therefore an important step towards a better understanding of the formation of the super-massive black holes that exist at the centre of the Milky Way and other galaxies."

In fact, the 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.

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