July 6, 2012
CSIRO Telescope Detects ‘Middleweight’ Black Hole
Lee Rannals for redOrbit.com - Your Universe Online
Astronomers have spotted the first known "middleweight" black hole, according to a publication in Science Express.
The black hole was found with a CSIRO radio telescope in a galaxy called ESO 243-49, which is about 300 million light-years away.
Before the black hole was found, astronomers had only known of supermassive black holes and "stellar mass" ones.
"This is the first object that we're really sure is an intermediate-mass black hole," Dr Sean Farrell, an ARC Postdoctoral Fellow at the University of Sydney and a member of the research team, wrote in the publication.
From what scientists understand so far, supermassive black holes are one million to a billion times the mass of the Sun, while stellar mass ones are three to thirty times the mass of the Sun.
"We don't know for sure how supermassive black holes form, but they might come from medium-size ones merging," CSIRO's Dr Ron Ekers, who studies supermassive black holes in the center of galaxies, said in the publication. "So finding evidence of these intermediate-mass black holes is exciting."
The middleweight black hole, HLX-1, was discovered in 2009 because it stood out as a very bright X-ray source.
Farrell said that while a number of other bright X-ray sources have been put forward, all those sources could be explained as resulting from lower mass black holes.
"Only this one can't. It is ten times brighter than any of those other candidates," he said in Science Express. "We are sure this is an intermediate-mass black hole – the very first."
He said that from studying other black holes, astronomers know that sucking in the gas creates X-rays. However, there is a reflux with the region around the black hole, shooting out jets of high-energy particles that hit gas around the black hole and generate radio waves.
"So what we tend to see is the X-ray emission and then, a day or two or even a few days later, the source flaring up in radio waves," Farrell said.
He speculates that a companion star traverses an eccentric orbit around the black hole, and when it gets close, the black hole strips gas from its partner, creating the X-ray flaring.
The brightness of the X-ray and radio flares have allowed the researchers to put a limit on the mass of the black hole at 90,000 times the mass of the Sun. However, Farrell said this is a conservative estimate, and could reach a lower figure of around 20,000 solar masses.
"There maybe lots of others out there that are not currently feeding, and so are not detectable, or are feeding at a very low rate, so they don't stand out as intermediate-mass black holes," Ekers said in Science Express.