HOW heavy can a pair of black holes be and still tango? Try 1 billion solar masses 鈥� the combined might of two black holes circling each other at the heart of a quasar 5 billion light years away.
A quasar is a galaxy with a supermassive black hole at its centre. Some quasars form when two galaxies merge, so should have two black holes at their cores. But these binary systems are far from easy to find. Todd Boroson and Tod Lauer of the National Optical Astronomy Observatory in Tucson, Arizona, stumbled upon one when they were sifting through a catalogue of 17,500 quasars found by the Sloan Digital Sky Survey.
The pair found two sets of broad hydrogen spectral lines in the light coming from J1536+0441, a quasar in the direction of the constellation Serpens Caput. Such signatures are caused by gas swirling into two black holes. 鈥淚t doesn鈥檛 smell like two ordinary quasars along the line of sight,鈥� says Lauer. 鈥淭his is a good solid case of a binary black hole quasar.鈥�
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The black holes weigh about 107.3 and 108.9 solar masses, and are separated by about 0.3 light years and have an orbital period of nearly 100 years.
See also: Colossal black holes seen in closest clinch yet
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