Earlier this year, astronomers discovered what appeared to be a pair of supermassive black holes circling toward a collision so powerful it would send a burst of gravitational waves surging through the fabric of space-time itself. 

    Now, in a study in the journal Nature, astronomers at Columbia University provide additional evidence that a pair of closely orbiting black holes is causing the rhythmic flashes of light coming from quasar PG 1302-102. 

   Based on calculations of the pair's mass--together, and relative to each other--the researchers go on to predict a smashup 100,000 years from now, an impossibly long time to humans but the blink of an eye to a star or black hole. Spiraling together 3.5 billion light-years away, deep in the Virgo constellation, the pair is separated by a mere light-week. By contrast, the closest previously confirmed black hole pair is separated by 20 light-years. 

    "This is the closest we've come to observing two black holes on their way to a massive collision," said the study's senior author, Zoltan Haiman, an astronomer at Columbia. "Watching this process reach its culmination can tell us whether black holes and galaxies grow at the same rate, and ultimately test a fundamental property of space-time: its ability to carry vibrations called gravitational waves, produced in the last, most violent, stage of the merger." 

    At the center of most giant galaxies, including our own Milky Way, lies a supermassive black hole so dense that not even light can escape. Over time, black holes grow bigger--millions to billions times more massive than the sun--by gobbling up stars, galaxies and even other black holes. 

 A supermassive black hole about to cannibalize its own can be detected by the mysterious flickering of a quasar--the beacon of light produced by black holes as they burn through gas and dust swirling around them. Normally, quasars brighten and dim randomly, but when two black holes are on the verge of uniting, the quasar appears to flicker at regular intervals, like a light bulb on timer. 

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http://www.eurekalert.org/pub_releases/2015-09/cu-nsf090915.php