An international team of astrophysicists and astronomers, led by Dr Youjun Lu of the National Astronomical Observatories of China, has found a supermassive pair of black holes in Markarian 231, the nearest quasar to Earth. The discovery of two black holes – one larger one and a second, smaller one – is evidence of a binary black hole and suggests that supermassive black holes assemble their masses through violent mergers.

Markarian 231, also known as UGC 8058, is a Type-1 Seyfert galaxy located 600 million light-years away from Earth. It has long tidal tails and a disturbed shape.

The galaxy was discovered in 1969 as part of a search of galaxies with strong UV radiation. Results from the first spectrum showed clear signs of the presence of a powerful quasar in the galactic center.

Later observations have revealed that the galaxy is undergoing an energetic starburst. Most dramatically a nuclear ring of active star formation with a rate estimated to be greater than 100 solar masses per year has been found in the center.

Dr Lu and co-authors looked at UV radiation emitted from the center of Markarian 231 from Hubble observations, then applied a model developed by Dr Lu to the spectrum of the galaxy. As a result, they were able to predict the existence of the binary black holes in it.

“We are extremely excited about this finding because it not only shows the existence of a close binary black hole in Markarian 231, but also paves a new way to systematically search binary black holes via the nature of their UV light emission,” said Dr Lu, a co-author of a paper published in the Astrophysical Journal (arXiv.org preprint).

“The structure of our Universe, such as those giant galaxies and clusters of galaxies, grows by merging smaller systems into larger ones, and binary black holes are natural consequences of these mergers of galaxies,” added co-author Prof Xinyu Dai of the University of Oklahoma.

So over time, the two black holes in Markarian 231 will collide and merge to form a quasar with a supermassive black hole.

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Chang-Shuo Yan et al. 2015. A probable Milli-Parsec Supermassive Binary Black Hole in the Nearest Quasar Mrk 231. ApJ 809, 117; doi: 10.1088/0004-637X/809/2/117