Scientists have detected ripples in space-time from the violent collision of two massive black holes that spiralled into one another far beyond the distant edge of the Milky Way.The black holes, each more than 100 times the mass of the sun, began circling each other long ago and finally slammed together to form an even more massive black hole about 10bn light years from Earth.The event is the most massive black hole merger ever recorded by gravitational wave detectors and has forced physicists to rethink their models of how the enormous objects form. The signal was recorded when it hit detectors on Earth sensitive enough to detect shudders in space-time thousands of times smaller than the width of a proton.“These are the most violent events we can observe in the universe, but when the signals reach Earth, they are the weakest phenomena we can measure,” said Prof Mark Hannam, the head of the Gravity Exploration Institute at Cardiff University. “By the time these ripples wash up on Earth they are tiny.”Evidence for the black hole collision arrived just before 2pm UK time on 23 November 2023 when two US-based detectors in Washington and Louisiana, operated by the Laser Interferometer Gravitational-wave Observatory (Ligo), twitched at the same time.The Laser Interferometer Gravitational-wave Observatory (Ligo) detector. Photograph: Caltech/MIT/LIGO LabThe sudden spasm in space-time caused the detectors to stretch and squeeze for one tenth of a second, a fleeting moment that captured the so-called ringdown phase as the merged black holes formed a new one that “rang” before settling down.Analysis of the signal revealed that the colliding black holes were 103 and 137 times the mass of the sun and spinning about 400,000 times faster than Earth, close to the theoretical limit for the objects.“These are the highest masses of black holes we’ve confidently measured with gravitational waves,” said Hannam, a member of the Ligo scientific collaboration. “And they’re strange, becau