LIGO Just Saw The Most Massive Black Hole Merger Ever Detected

The Laser Interferometer Gravitational Wave Observatory (LIGO) has seen over 300 black hole mergers in its short time in operation, and now it’s seen an event so large—and so rare—that it challenges the extent of modern astronomical theory.

The event was between two black holes in the “intermediate” size range—that is, bigger than a so-called stellar mass black hole, and smaller than a so-called supermassive black hole.

Black holes in this intermediate range are thought to be uncommon, since stars in this size range tend to expel most of their mass in supernova events and fail to collapse into black holes. So, for a black hole in this range to exist, it likely had to begin smaller and slowly gobble up mass to grow. In a sense, this makes them proto-supermassive black holes. Because proto-supermassive black holes are rare, an interaction between two of them is ...