On August 17, the signals from two merging neutron stars reached Earth after a journey of 130 million light years. After an 11 billion year dance, these remnants of once-massive, blue stars that died in supernovae so long ago spiraled into one another after emitting enough gravitational radiation to see their orbits decay. As each one moves through the changing spacetime created by the gravitational field and motion of the other, its momentum changes, causing the two masses to orbit one another more closely over time. Eventually, they meet, and when they do, they undergo a catastrophic reaction: a kilonova. For the first time, we’ve recorded the inspiral and merger in the gravitational wave sky, noticing it in all three detectors (LIGO Livingston, LIGO Hanford, and Virgo), as well as in the electromagnetic sky, from gamma rays all the way through the optical and into the radio. At last, gravitational wave astronomy is now a part of astronomy.From the very first binary neutron star system ever discovered, we knew that gravitational radiation was carrying energy away. It was only a matter of time before we found a system in the final stages of inspiral and merger.