Pair of black holes prepare to take the plunge

SEATTLE — Two supermassive black holes are preparing to face off in the center of a distant galaxy. The cuddled-up pair are closer to each other than any other known black hole duo, providing astronomers a first peek at the final stages of a possible collision.

The two black holes live roughly 3.7 billion light-years away in a quasar, the ferociously bright core of a galaxy lit up by superheated gas spiraling onto a supermassive black hole. Quasars typically vary in brightness randomly. But the light from this quasar, designated PG 1302-102, varied with a steady period over the last two decades, suggesting that two black holes were working together, Caltech astronomer George Djorgovski reported January 7 at a meeting of the American Astronomical Society. The research also appears online January 7 in Nature.

Separated by just a few hundredths of a light-year, the black holes will probably spiral together and merge to form a single behemoth black hole in roughly 1 million years. Theories of galaxy formation predict that close black hole pairs should be relatively common, arising out of the collision of two galaxies. But because they’re so far away, binary black holes are an elusive quarry.