hlx1 Astronomers Confirm First Middleweight Black Hole Discovered

A multinational team working in Australia have discovered a middleweight black hole, the first of it's kind.

Astronomers in Australia have confirmed a remarkable discovery: the first known “middleweight” black hole. Researchers from Australia, France, Britain and the United States worked together to refine estimates of the size of the black hole, whose existence was first published in Nature in 2009.

Prior to this find, the only black holes that were confirmed to exist were so called “stellar mass” back holes, up to 30 solar masses, or 30 times the mass of the Sun, and supermassive black holes with masses in the region of a million to a billion solar masses.

The black hole, named HLX-1, or “hyper-luminous X-ray source 1”, is located about 300 million light years away in a galaxy called ESO 243-49 and falls in between the two previously known categories in terms of mass, at around 20000 solar masses.

The research team was led by Dr Sean Farrell from the School of Physics at the University of Sydney. Explaining the discovery, Dr Farrell said “black holes are areas where the matter is so densely squeezed into a small space, that it makes gravity pull strongly enough to stop light from escaping” and “black holes change state from a high luminosity to a low luminosity X-ray state, and back again. As they change state they release jets of superfast moving plasma which can be measured by the radio waves emitted.”

Using the Australian Telescope Compact Array and NASA’s Swift satellite, the team analysed radio emissions during two state transitions of HLX-1 in September and December of 2010, and August 2011. They found that it exhibited the same radio activity shown by black holes when they change state.

In the words of Dr Emil Lenc, “we know that when black holes suck in gas they create X-rays, but there’s a sort of reflux, with the region around the black hole shooting out jets of high energy particle that hit gas around the black holes 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 flares up in radio waves.” As HLX-1 changes state, it undergoes this “transient jet ejection”.

By examining the radio emissions released by HLX-1, the team were able to calculate its size. Dr Farrell said “we’ve been able to refine our estimate of how big HLX-1 is to be around 9 x 103 times the size of our sun and 9 x 104 times the size of our sun.”

“It’s further proof that HLX-1 is indeed sized as an intermediate mass black hole.”