The University of Southampton

Intermediate Mass Black Holes and revelations

17 February 2012

Just like the popular Muse album ‘Black Holes and Revelations’, a research team including Dr Tom Maccarone and Professor Christian Knigge from the University of Southampton has found a newly discovered type of black hole – an Intermediate Mass Black Hole – which reveals clues on how galaxies are formed.

The research, published this week in the USA’s Astrophysical Journal, examines how these Intermediate Mass Black Holes form, furthering our understanding of how supermassive black holes form and therefore how galaxies may be created and evolve.

The first Intermediate Mass Black Hole, called HLX-1, was discovered in 2009. Focusing on HLX-1 as the prototype of this new class of black hole, the new paper details the detection of the presence of a very young massive cluster of stars around HLX-1.

“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,” explained Dr Sean Farrell, from the Sydney Institute for Astronomy at the University of Sydney, who led the study.

“Astronomers have classified black holes into stellar mass black holes, which are up to tens of times the mass of our Sun, and supermassive black holes, which are millions to billions of times the mass of our Sun. HLX-1 lies in between at around 20 000 times the mass of our Sun.”

Using NASA’s Hubble and Swift space telescopes and new modeling techniques developed for this research, the researchers have taken a closer look at their HLX-1 black hole. The fact that it’s a very young cluster of stars indicates that the newly discovered Intermediate Mass Black Hole may have originated as the central black hole in a very low mass dwarf galaxy, that has been swallowed by the massive galaxy that it now resides in.

Dr Tom Maccarone of Physics and Astronomy at the University of Southampton comments: “Even with the fantastic image quality of Hubble, this object still looks like a point of light. What really complicated things was that we had to sort out how much light was coming from the disk of gas falling toward the black hole, and how much light was coming from the stars in the general vicinity of the black hole.

“Fortunately, we had made images with Hubble in many different colours of light, and we were able to use the colours plus some models of the colours for groups of stars both to sort out how much light was coming from stars versus disk, and how many hot, blue stars versus cool, red stars we had.”

The formation of stellar mass black holes through the collapse of massive stars is well accepted, but it is not yet completely clear how the supermassive black holes are formed. Supermassive black holes may form through the merger of Intermediate Mass Black Holes, so studying Intermediate Mass Black Holes and the environments in which they are found has important implications for a wide range of important questions in modern astrophysics.

“Intermediate Mass Black Holes are a crucial missing link between stellar mass and supermassive black holes, and may turn out to be the building blocks of the supermassive black holes found in the centres of galaxies. Our own Milky Way galaxy may be filled with them,” adds Dr Farrell.


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