A collision observed between two black holes, each more massive than a hundred suns, is the largest merger of its kind ever recorded, according to new research.

The merger wasn’t just the biggest ever, but also an event so rare that it challenges existing models for black hole genesis.

“It’s the most massive [merger] so far,” says Mark Hannam, a physicist at Cardiff University, UK, and part of the LVK Collaboration, a wider network of gravitational-wave detectors that encompasses LIGO, Virgo in Italy and KAGRA in Japan. It’s “about 50% more than the previous record holder”, he says.