Last winter, a team of Caltech astronomers reported that two supermassive black holes appeared to be spiraling together toward a cataclysmic collision that could bring down the curtains in that galaxy. The evidence was a rhythmic flickering from the galaxy’s nucleus, a quasar known as PG 1302-102, which Matthew Graham and his colleagues interpreted as the fatal mating dance of a pair of black holes with a total mass of more than a billion suns. Their merger, the astronomers calculated, could release as much energy as 100 million supernova explosions, mostly in the form of violent ripples in space-time known as gravitational waves that would blow the stars out of that hapless galaxy like leaves off a roof.
As the black holes and their attendant disks swing around each other at high speeds, the light from the disk that is coming toward us receives a boost from relativistic effects — a so-called Doppler boost — the way a siren grows louder and more high-pitched as it approaches, giving rise to a periodic increase in brightness every five years. The Columbia astronomers’ model predicts that the variation would be two or three times greater in ultraviolet light than in visible light. And that is exactly what they found when they compared archival data from the Hubble Space Telescope and NASA’s Galex space telescope to the visible-light data previously analyzed by Dr. Graham’s group. FULL REPORT