In a single galaxy, two massive black holes are spiraling toward each other in a gravitational dance that will end in a few hundred million years, when the black holes merge, astronomers report.
They had good reason to suspect there’d be such pairs. Accumulating evidence has revealed black holes in galactic centers and mergers of galaxies. So, it follows that some galaxies ought to have two black holes. “It was starting to become a little embarrassing that there was actually so little evidence of any [such] galaxies,” says Roeland van der Marel of the Space Telescope Science Institute in Baltimore.