New class of black hole discovered

Intermediate-mass black holes could be the key step in their evolution

NGC 2276-3c, as seen in X-ray and optical data from Chandra, Hubble and the Digitized Sky Survey (main pic) and in radio emissions by the European Very Long Baseline Interferometry Network (inset)

Credit: X-ray: NASA/CXC/SAO/M.Mezcua et al & NASA/CXC/INAF/A.Wolter et al; Optical: NASA/STScI and DSS; Inset: Radio: EVN/VLBI

By Russell Deeks

An object discovered 100 million lighyears from Earth in the galaxy NGC 2276 may be a missing piece in the puzzle of black hole evolution. Scientists from a number of research institutions worldwide have been using the Chandra X-ray Observatory, Hubble Space Telescope and European Very Long Baseline Inteferometry Network (EVN) to study 2276-3c, as it’s been labelled. They have concluded that it is in fact an entirely new class of object, which they are calling an Intermediate-Mass Black Hole, or IMBH for short.

The black holes that we know about so far fall into one of two categories. Stellar-mass black holes have from five to 30 times the mass of the Sun, while the supermassive black holes that sit at the centre of most, if not all, galaxies have masses that are millions or even billions of times more than that of the Sun. Until now, no black holes had been discovered that sat in between these two extremes of mass – but NGC 2276-3c seems to fit neatly into that gap.

Using Chandra and EVN measurements of the object’s X-ray and radio emissions, and drawing on a known relationship between such emissions and mass, scientists have been able to pinpoint the mass of NGC 2276-3c at around 50,000 times that of the Sun. EVN radio data further reveals an inner jet of radio emissions that extends six lightyears from the object, while observations using the Karl Lansky Very Large Array show larger-scale emissions extending outwards up to 2,000 lightyears. This emission ‘wind’ is believed to be the reason why no young stars exist within 1,000 lightyears of the object, yet many appear around the edges of the emission zone.

It's thought that IMBHs like NGC 2276-3c may be the ‘seeds’ from which supermassive black holes eventually grow, and the object is therefore likely to attract considerable scientific interest for some time to come. But it's not the only black hole to be discovered this week: a quasar named SDSS J0100+2802 has also been found by astronomers from Peking University and the University of Arizona, that has a 12 billion solar mass black hole at its centre, and that is thought to be just 900 million years younger than the Universe itself.

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