A tiny dot belies great violence

This is an image captured by NASA’s Chandra X-ray observatory. It shows neither a star nor a planet, but a bright X-ray disc, the remnants of a star ripped apart by the gravitational pull of a supermassive black hole.

Essentially a bright flash of light, the disc, dubbed ASASSN14-li, was first recorded in 2014 and has been an object of fascination for astronomers ever since. By monitoring the behaviour of the disc – using a battery of terrestrial and orbiting telescopes – researchers have been able to directly measure the spin of the predatory black hole.

A team led by Dheeraj Pasham of the Massachusetts Institute of Technology in the US found that the hole, which lurks some 290 million light years away, has an event horizon – beyond which not even light can escape – about 300 times the size of Earth. 

Spin rate was determined by observing 300,000 cycles in which the brightness of the X-ray disc waxed and waned. The event horizon was calculated to rotate fully every two minutes.

The results of the research appear in the journal Science. A full preprint is available here.

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