Phases of a binary coalescence and the gravitational wave produced during merger.
Every accelerating massive object emits gravitational waves. These waves can be visualized as distortions in space-time and are one of the direct strong-field tests of Einstein's Theory of Relativity. It was in 2015 that these waves were first detected (by LIGO) so the detection of gravitational waves is relatively new! While the detection of gravitational waves is a big achievement, this is just the beginning. By 2040 we are hoping to send LISA to space which will enable us to detect gravitational waves emitted by supermassive black holes. Supermassive black holes are millions of times the mass of our sun and almost every galaxy has one at its center.