The ‘Final Parsec Problem’
Two black holes are entwined in a gravitational tango in this artist’s conception. Supermassive black holes at the hearts of galaxies are thought to form through the merging of smaller, yet still massive black holes, such as the ones depicted here. NASA
Binary black holes, as the name suggests, are a system composed of two black holes locked in close orbit around each other. Since most galaxies in the universe are believed to harbor one supermassive black hole at their center, the presence of a binary system is conclusive evidence of a galactic merger. Although only a few candidates for such a system have ever been detected, astronomers at the University of Maryland, College Park, now believe that they have discovered incontrovertible evidence of such black-hole twins.