Black holes are getting stranger—even to astronomers, who've now detected the signal from a long-ago violent collision of two black holes that created a new one of a size that had never been seen before. "It's the biggest bang since the Big Bang observed by humanity," says Caltech physicist Alan Weinstein, who was part of the discovery team. Black holes are compact regions of space so densely packed that not even light can escape. Until now, astronomers only had observed them in two general sizes, reports the AP. There are "small" ones called stellar black holes that are formed when a star collapses and are about the size of small cities; scientists thought these didn't get much bigger than 70 times the mass of our sun. Supermassive black holes are millions, maybe billions, of times more massive than our sun, and entire galaxies revolve around them.
According to astronomers' calculations, anything in between didn't quite make sense, because stars that grew too big before collapse would essentially consume themselves, leaving no black holes. Then, in May 2019, two detectors picked up a signal that turned out to be the energy from two large stellar black holes crashing into each other. One was 66 times the mass of our sun and the other a husky 85 times the mass of the sun. The end result: the first ever discovered intermediate black hole, at 142 times the mass of the sun. Lost in the collision was an enormous amount of energy in the form of a gravitational wave, which physicists in the US and Europe detected last year. After deciphering the signal and checking their work, scientists published the results Wednesday in Physical Review Letters. This crash happened about 7 billion years ago but is only being detected now because it's incredibly far away. (Read much more on the study here.)