The closest quasar to Earth might harbor a rare pair of supermassive black holes. The dark duo is probably left over from a galaxy collision, researchers report, and offers a way to test theories about gravity and the growth of galaxies.
Black hole couples should pop up in the center of pretty much every galaxy at some point, as galaxies grow by colliding with one another. This galactic cannibalism eventually brings together the black holes that reside in their centers. “If we cannot find any binary black holes in the centers of big galaxies, that means our understanding of galaxy formation may be wrong,” says Youjun Lu, an astrophysicist at the National Astronomical Observatories of the Chinese Academy of Sciences in Beijing.