First 'middleweight' black hole confirmed

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SYDNEY, July 9 (UPI) -- Astronomers using an Australian radio telescope say they've confirmed the existence of the first known "middleweight" black hole.

Before the discovery of HLX-1, or "hyper-luminous X-ray source 1, in a galaxy about 300 million light-years from Earth, astronomers had good evidence for only supermassive black holes, a million to a billion times the mass of the Sun, and "stellar mass" ones, just three to 30 times the mass of the Sun.

Outbursts of super-hot gas observed with a radio telescope of the Commonwealth Scientific and Industrial Research Organization clinch the identity of HLX-1, first detected by astronomers at the Harvard-Smithsonian Center for Astrophysics in February, as a long-sought "middleweight" example, a CSIRO release reported.

"This is the first object that we're really sure is an intermediate-mass black hole," said Sean Farrell at the University of Sydney, a member of the research team that included astronomers from France, Australia, Britain and the United States.

"A number of other bright X-ray sources have been put forward as possibly being middleweight black holes. But all of those sources could be explained as resulting from lower mass black holes," Farrell said. "Only this one can't. It is 10 times brighter than any of those other candidates. We are sure this is an intermediate-mass black hole -- the very first."

The finding could help astronomers understand more about all types of black holes, he said.

"We don't know for sure how supermassive black holes form, but they might come from medium-size ones merging. So finding evidence of these intermediate-mass black holes is exciting."