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Durham University News

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Research finds intriguing member of black hole family tree

(6 March 2015)

A newly discovered cosmic object may help provide answers to some long-standing questions about how black holes evolve and influence their surroundings, according to a new study involving Durham University.

Using NASA's Chandra X-ray Observatory, an international team of astronomers discovered what appears to be an “intermediate-mass black hole” (IMBH) in the arm of a spiral galaxy about 100 million light years from Earth.

The object – called NGC-2276-3c – could be evidence of a missing relative in the black hole family.

There is a lot of evidence for smaller black holes that contain about five to 30 times the mass of our own Sun, and for so-called supermassive black holes that live at the centre of galaxies and can be millions or billions of times heavier than the Sun.

As their name suggests, IMBHs represent a class of black holes that fall in between these two well-established groups, with masses in the range of a few hundred to a few hundred thousand solar masses.

NGC 2276-3c has traits similar to both stellar-mass black holes and supermassive black holes, potentially helping to tie the whole black hole family together.

One reason that IMBHs are important is that they could be the seeds from which supermassive black holes formed in the early universe.

Dr Tim Roberts, of the Centre for Extragalactic Astronomy at Durham University, said: "Astronomers have been looking very hard for these medium-sized black holes.

"There have been hints that they exist, but the IMBHs have been acting like a long-lost relative that isn't interested in being found."

In addition to its mass, another remarkable property of NGC-2276-3c is that it has produced a powerful radio jet extending for up to 2,000 light years.

The region along this jet that extends up to about 1,000 light years from NGC-2276-3c seems to be missing young stars. This provides evidence that the IMBH may have had a strong influence on its environment, as the jet could have cleared out a cavity in the gas needed to form new stars and suppressed star formation.

Further studies of the NGC-2276-3c jet could provide insight into the potentially large effects that supermassive black hole seeds in the early Universe had on their surroundings.

The location of NGC-2276-3c in the spiral arm of its host galaxy also raises another question – was it formed within the galaxy or did it come from the centre of a dwarf galaxy that collided and merged with its current host galaxy in the past?

Current research on the galaxy suggests that there is a high rate of star formation in the IMBH’s host galaxy, supporting the idea that two galaxies may have once collided.

The results appear in a paper in the journal Monthly Notices of the Royal Astronomical Society.

Dr Roberts was co-author on a paper looking at the radio jet coming from the IMBH, led by Dr Mar Mezcua, at the Harvard-Smithsonian Center for Astrophysics in the USA.

Dr Roberts was funded by the Science and Technology Facilities Council (STFC).

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

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