An exploding star spotted 30 years ago in a nearby galaxy appears to be a newborn black hole, astronomers have reported.
X-ray observations suggest the supernova, called SN 1979C, is a black hole in the making, a team of US and European astronomers said.
"If our interpretation is correct, this is the nearest example where the birth of a black hole has been observed," Daniel Patnaude of the Harvard-Smithsonian Center for Astrophysics in Massachusetts, who helped lead the study, said in a statement.
Amateur astronomer Gus Johnson of Maryland spotted the supernova in 1979 at the edge of a galaxy called M100, and astronomers have been peering at it since. Light and X-rays from the collapse have taken 50 million years to travel to Earth at the speed of light - 300,000km a second, or about 10 trillion km a year.
Nasa's Chandra X-ray Observatory, the European Space Agency's XMM-Newton and the German ROSAT observatory have seen that it emits a steady source of bright X-rays.
Analysis of the X-rays support the idea that the object is a black hole and that it is either being fed by material falling back from an initial supernova, or perhaps from a twin star, the astronomers said.
Scientists believe black holes can be formed in a number of ways - in this case by a star about 20 times the mass of our Sun going supernova and then collapsing into an object so dense that it sucks surrounding material into its core.