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This is an artist’s impression of the source HLX-1

A group of international astronomers in the UK, France and the USA, led by the University of Leicester, have found proof to confirm the distance and brightness of the most extreme ultra-luminous X-ray source, which may herald a new type of Black Hole.

The X-ray source, HLX-1, is the most extreme member of an extraordinary class of objects — the ultra-luminous X-ray sources — and is located in the galaxy ESO 243-49 at a distance of ~300 million light years from the Earth.

The astronomers’ findings confirm that the extreme luminosity (which is a factor of ~100 above most other objects in its class, and a factor of ~10 higher than the next brightest ultra-luminous X-ray source) is correct.

This is forcing scientists to rethink their theories on the maximum brightness of ultra-luminous X-ray sources, and provides support to the idea that HLX-1 may contain an intermediate mass black hole.

This latest result will be reported September 8 in the scientific journal, The Astrophysical Journal.

Using the European Southern Observatory’s (ESO’s) Very Large Telescope (VLT) in Chile, the team have obtained an optical spectrum of their record breaking ultra-luminous X-ray source (HLX-1) in the distant galaxy ESO 243-49.

Their findings enable them to show conclusively that HLX-1 is indeed located within this galaxy, and is neither a foreground star nor a background galaxy. The main implication of this discovery is that ultra-luminous X-ray sources such as HLX-1 can be brighter than was originally thought, which is consistent with at least the brightest of them hosting intermediate mass black holes.

A black hole is an ultra-dense object with such a powerful gravitational field that it absorbs all the light that passes near it and reflects nothing.

While astrophysicists have suspected that an intermediate class of black hole might exist, with masses between a hundred and several hundred thousand times that of the Sun, such black holes had not previously been reliably detected and their existence has been fiercely debated among the astronomical community.

The VLT enabled the team of researchers to confirm the detection of HLX-1 in optical wavelengths and to measure a precise distance to it.

The lead author of the paper reporting this result, Dr Klaas Wiersema of Leicester’s Department of Physics and Astronomy, commented: “After our earlier discovery of the very bright X-ray source, we were very keen to find out just how far away it really is, so that we can work out how much radiation this black hole produces.

“We could see on images taken with big telescopes that a faint optical source was present at the location of the X-ray source, located near the core of a large and bright galaxy.

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