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
