First Middleweight Black Hole Found

A research team using the Compact Array radio telescope from the Commonwealth Scientific and Industrial Research Organization (CSIRO) has identified the first "middleweight" black hole.

By scanning the skies using a radio telescope, the scientists in a paper published in Science, stated that they observed superhot gas shooting out from Hyper-luminous X-ray source 1, or HLX-1.

Until now, only supermassive black holes, weighing a million to a billion times the sun, and stellar black holes, weighing three to tens of times our sun, were the only types of black holes identified.

"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.

HLX-1 resides in the galaxy ESO 243-49, which is around 300 million light years away.

The medium-sized black hole could help shed light on the way other 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 Dr. Ron Ekers, a CSIRO member who studies supermassive black holes at the center of galaxies.

HLX-1 was first noticed because it emitted very bright X-rays. Typically, a black hole will shoot out bright X-rays because it will suck in gas from a nearby star or gas cloud and superheat it.

"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," Dr. 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."

After shooting out bright X-rays, the black hole emits radio waves as a byproduct sometime after. Dr. Farrell and the other astronomers were able to accurately predict the emission of these radio waves.

Dr. Farrell believes that there is a star with an eccentric orbit around HLX-1, and whenever it gets close enough to the black hole, the black hole sucks in some of its gas and its X-rays shine brighter.

Based on the brightness of the X-ray emissions, the team believes that the black hole could have an upper weight limit of 90,000 times the sun. They conservatively estimate a weight of 20,000 solar masses.