"Black Hole Milky Way" by Gallery of Space Time Travel / CC BY-SA 2.0

Colliding black holes may have created a surprising flare of light

Jun 25, 2020

By Emily Conover

In spite of their dark reputations, two black holes may have set off a cosmic light show.

Subtle gravitational rumbles from a collision of two black holes may have been accompanied by a flare of light about a month later, physicists report June 25 in Physical Review Letters. It’s a surprising conclusion given black holes’ propensity to swallow up light and matter. “The normal expectation has been they just merge and all you would detect is gravitational waves,” says astrophysicist Matthew Graham of Caltech.

But scientists, not ones to rest on assumptions, wanted to check if that expectation was right. To look for a flare, Graham and colleagues combed through data from the Zwicky Transient Facility at the Palomar Observatory in California, which repeatedly images the sky, searching for short-lived changes called transients. They found that about 34 days after the gravitational waves were detected in May 2019, a blaze of light appeared in the vicinity of sky that the gravitational waves had pinpointed. This outburst was associated with a known quasar, a glowing celestial object made up of a disk of gas surrounding a supermassive black hole (SN: 3/29/16). The gargantuan black hole in question boasts a mass 100 million times that of the sun.

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