First middle-weight black hole discovered
Outer space is a place of extremes - extreme cold and heat, extreme distances, and extreme size. So, the observation of a middle-weight black hole is something of an anomaly.
Outbursts of super-hot gas seen with a radio telescope have helped scientists identify the first known "middleweight" black hole, which is called HLX-1 ("hyper-luminous X-ray source 1") and lies in a galaxy about 300 million light-years away.
"This is the first object that we're really sure is an intermediate-mass black hole," said Dr Sean Farrell, an ARC Postdoctoral Fellow at the University of Sydney and a member of the research team, which included astronomers from France, Australia, the UK and the USA.
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The finding happened by chance when researchers came upon a very bright X-ray source caused by heated gas being sucked into the black hole.
"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 ten times brighter than any of those other candidates. We are sure this is an intermediate-mass black hole - the very first."
Until now, only 'small' black holes (just 3 to 30 times the mass of the Sun) and supermassive black holes (equal to millions of solar masses) had been found. Not only does the finding fill in the hole left by these extremes, but it could give scientists a better idea of how supermassive black holes form.
"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," said Ron Ekers of Australia's national space agency (CSIRO) who studies supermassive black holes in the centers of galaxies, according to UPI.
To truly identify a black hole, you need two things: X-ray emissions created by the inflow of gas, and what Farrel calls "a sort of reflux" of radio waves generated when shooting jets of high-energy particles hit gas around the black hole.
Natalie Webb of the Université de Toulouse in France and her research team detected those radio emissions at HLX-1, which adds to the evidence that this is indeed a middle-weight black hole, reports Time.
"When my group initially found HLX-1 in 2009 using a simple approach, I was extremely skeptical," Webb told Time. "However, we have observed it in all different wavelengths, and so far it is the first intermediate-mass black-hole candidate that has stood up to so many tests."
The brightness of the X-ray and radio flares allowed the team to estimate that the largest size of the black hole could be 90,000 times the mass of the Sun. However, Farrell says that this is a conservative estimate, and for a variety of reasons a lower figure of around 20,000 solar masses is more likely.
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