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New findings build on discovery made at University of Leicester

A research team led by Dr Sean Farrell, formerly of the University of Leicester and now at the Sydney Institute for Astronomy at the University of Sydney, has found that a newly discovered type of black hole - an Intermediate Mass Black Hole – reveals clues on how galaxies are formed and where the popular Muse album ‘Black Holes and Revelations’ may have found some inspiration.

The research that examines how these Intermediate Mass Black Holes form, which furthers our understanding of how galaxies may form was published in the USA’s Astrophysical Journal February 2012.

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

Picture of HLX-1 Credits: NASA, ESA, and S. Farrell.
Focusing on HLX-1 as the prototype of this new class of black hole, the new 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 objects where the matter is so densely squeezed into a small space, that it makes gravity pull strongly enough to stop light from escaping. Astronomers have classified black holes into stellar mass black holes (up to tens of times the mass of our Sun) and supermassive black holes (millions to billions the mass of our Sun).

“HLX-1 lies in between at around 20 000 times the mass of our Sun, “says Dr Farrell.

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

Klaas Wiersema, from the University of Leicester Department of Physics and Astronomy, said: “The combination of nearly simultaneous measurements at optical wavelengths (Hubble) and X-rays (Swift X-ray telescope) allowed us to firmly establish where the optical light in this source originates. Swift is the perfect satellite to do these X-ray observations, as it combines good sensitivity with the ability to observe a source very frequently. Swift data are very accurately calibrated and analysed by the Swift team based at the University of Leicester."

Co-Author Dr Mathieu Servillat from the Harvard-Smithsonian Centre for Astrophysics says "For a unique source we needed Hubble, a unique telescope, to enable such a precision to understand the environment of the black hole and witness what is probably a merger in progress with its host galaxy."

“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,” explained Dr Farrell.

“This has really important implications for how supermassive black holes form, and therefore how galaxies form and “Before this finding, 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 understand where they come from,” says 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.”evolve.”

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.”

Picture of HLX-1
credits: NASA, ESA, and S. Farrell.