I'd like to understand the details behind the LIGO experiment a bit better: How do scientists know that the gravitational waves detected by LIGO originated from two specific black holes (located a billion light years away)? Does the LIGO result confirm the existence of black holes? Was it only after gravitational waves were detected by LIGO, that scientists tried to figure out from which location the gravitational waves originated? i.e. post-hoc deduction There was a "dud" gravitational wave detection in 2014 by the BICEP2 telescope located at the South Pole. What makes scientists so confident this time that the LIGO results aren't a dud?