WASHINGTON — An exploding star spotted 30 years ago in a nearby galaxy appears to be a newborn black hole, astronomers reported on Monday. X-ray observations suggest the supernova, called SN 1979C, is a black hole in the making, a team of U.S. 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 — 186,000 miles (300,000 km) a second, or about 6 trillion miles (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.