Thomas P. Sotiriou

A black hole merger is not a silent impact. The newborn hole quivers and decays, emitting gravitational waves — ripples in space itself. This signal is called the 'ringdown,' and it resembles the fading chime of a bell: it has a fundamental tone and several overtones.

In the centers of many galaxies slumber supermassive black holes, surrounded by accretion disks and the activity of active galactic nuclei. When a compact object — such as a stellar-mass black hole — orbits them, a gravitational duet is born.