The world's gravitational wave detectors just wrapped up their longest and most productive observation campaign, capturing 250 new collisions over two years of continuous listening. These ripples in spacetime, created by black holes and neutron stars spiralling into each other across the universe, have given scientists their first direct evidence for Stephen Hawking's 1971 theory about black hole surface areas, revealed second generation black holes born from previous mergers, and detected the most massive black hole collision ever observed. The haul represents over two thirds of all gravitational waves ever detected.