Black holes are weird enough, but in March astronomers found signs of something even stranger: twin massive black holes orbiting tightly around each other. Such objects have been long predicted but never verified.
Todd Boroson and Tod Lauer at the National Optical Astronomy Observatory in Tucson found what they think is a dual black hole while examining more than 17,000 quasars in the Sloan Digital Sky Survey, which obtained data, images, and spectra of more than one-fourth of the sky. The two objects (a 20-million-solar-mass hole and a billion-solar-mass partner) seem to be separated by just one-third of a light-year, less than one-tenth the distance from the sun to the closest star.
In theory the universe should be littered with black hole multiples. All sizable galaxies are thought to be born with black holes at their centers, and each time galaxies collide and merge the expanded galaxy should collect a new one. But binary black holes are difficult to find. Astronomers have found dozens of quasars with similar double lines of emission, but the signatures are usually attributed either to a single black hole or to two galaxies passing close together.
Boroson and Lauer are optimistic that they have the real deal this time. “We’re convinced it is different from every other object we’ve studied,” Boroson says.