Starburst observed 30 years ago may hide 'nearby' black hole

Astronomers believe they have witnessed the birth of a nearby black hole, formed when a massive star collapsed in on itself creating a gravitational field so strong that not even light could escape. The collapsed star, which was 20 times more massive than the Sun, created a stellar explosion, or supernova, in the M100 galaxy in the Virgo cluster, 50 million light years from Earth.

The supernova, which was observed by an amateur astronomer in 1979 and called SN 1979C, has been analysed by powerful astronomical instruments including Nasa's Chandra X-ray Observatory. These have provided crucial evidence suggesting that a black hole is hidden behind the light emitted from the explosion.

Data from the Chandra observatory, Nasa's Swift satellite, the European Space Agency's XMM-Newton and the German Rosat observatory revealed a bright source of X-rays from the supernova that remained steady from 1995 to 2007, suggesting the object is a black hole perhaps being fed by material falling back into it.

"If our interpretation is correct, this is the nearest example where the birth of a black hole has been observed," said Daniel Patnaude of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts, who led the study.

More distant black holes had been detected by analysing huge explosions called gamma-ray bursts, but SN 1979C belongs to a different class of supernovas that are not associated with gamma-ray explosions.

Scientists believe that such supernovas are in fact the most common way that black holes are created, which is why the nearby SN 1979C is so interesting, said Abraham Loeb of the Harvard-Smithsonian Centre for Astrophysics.

"This may be the first time the common way of making a black hole has been observed. However, it is very difficult to detect this type of black hole birth because decades of X-ray observations are needed to make the case," Dr Loeb said.