'It just sounds like a thud': astronomers hear biggest cosmic event since big bang

Researchers believe noise was two black holes colliding around 7 billion years ago, creating a previously unseen class of stellar object

Scientists have announced the detection of a signal from a long-ago collision between two black holes that created a new one of a size never seen before.

It's the biggest bang since the big bang observed by humanity," said Caltech professor of physics Alan Weinstein, who was part of the discovery team.