Black hole sheds light on how galaxies are created

16 February 2012

The Sydney Institute for Astronomy's Dr Sean Farrell is leading the team exploring how galaxies are formed
The Sydney Institute for Astronomy's Dr Sean Farrell is leading the team exploring how galaxies are formed

A newly discovered type of black hole - an Intermediate Mass Black Hole - can help us understand how galaxies are formed, a research team led by Dr Sean Farrell, at the Sydney Institute for Astronomy at the University of Sydney, has found.

The research, published in the USA's Astrophysical Journal, examines how these Intermediate Mass Black Holes form, which furthers our knowledge of how galaxies may form.

In 2009, a team led by Dr Farrell, discovered the first Intermediate Mass Black Hole, called HLX-1, and published their findings in the prestigious journal Nature.

Focusing on HLX-1 as the prototype of this new class of black hole, the most recent paper details how Dr Farrell's team has detected 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 Farrell.

"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 is around 20000 times the mass of our Sun," said Dr Farrell.

Using NASA's Hubble and Swift space telescopes and new modeling techniques developed for this research, Dr Farrell and his team have taken a closer look at their HLX-1 black hole.

Co-author of the paper, Dr Mathieu Servillat, from the Harvard-Smithsonian Centre for Astrophysics, said, "For a unique source we needed a unique telescope - Hubble enabled enough precision in the images to allow us to understand the environment of the black hole and witness what is probably a merger in progress with its host galaxy."

Dr Farrell explained further, "Our latest finding is that we've detected evidence for a very young massive cluster of stars around the HLX-1 black hole. The fact that it's a very young cluster of stars indicates that our 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.

"This has really important implications for how supermassive black holes form, and therefore how galaxies form and evolve.

"Before this we had very strong evidence for the existence of Intermediate Mass Black Holes, but we weren't sure where they were formed. Now we may be able to understand where they come from," said Dr Farrell.

"This conclusion opens up many other opportunities for us to begin targeted observations, mainly with NASA's Chandra space telescope, in order to find more potential Intermediate Mass Black Holes."

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," said Dr Farrell.

"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."

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