BLACK HOLE BILLIARDS
Around these behemoths, smaller black holes weirdly collide
Reported by Meghan Bartels
Take three black holes and throw them into the disc surrounding a supermassive black hole and things get weird. That’s the conclusion of new research digging into a particularly strange gravitational-wave event that scientists observed in May 2019. Gravitational waves are the ripples in space-time caused by, among other dramatic events, the mergers of black holes. But this particular observation didn’t match other collisions scientists have caught: it resulted in a black hole in the mid-size range that scientists can barely see, much less explain, and some force was stretching the typically circular dance as the behemoths approached each other.
“The gravitational-wave event GW190521 is the most surprising discovery to date. The black holes’ masses and spins were already surprising, but even more surprising was that they appeared not to have a circular orbit leading up to the merger,” said Imre Bartos, a physicist at the University of Florida and coauthor of the new research. Astronomers name gravitationalwave signals with the date they were observed, so GW190521 marks a gravitational wave detected on 21 May 2019.