On the morning of 17th August 2017, a ripple in space passed through our planet, detected by the LIGO and Virgo gravitational wave detectors. This cosmic disturbance came from a pair of neutron stars colliding at one third the speed of light in the galaxy NGC4993, 130 million light years from Earth. The two neutron stars have been orbiting each other for most of the history of the universe, getting closer and closer until they merged into a doughnut-shaped unstable neutron star before finally collapsing as a black hole.