This image is a still from a video of a numerical simulation of a heavy black-hole merger (GW190521). The two black holes inspiral and merge, emitting gravitational waves. The black holes have large and nearly equal masses, with one only 3% more massive than the other. The simulated gravitational wave signal is consistent with the observation made by the LIGO and Virgo gravitational wave detectors on May 21st, 2019 (GW190521). Credit: N. Fischer, H. Pfeiffer, A. Buonanno (Max Planck Institute for Gravitational Physics), Simulating eXtreme Spacetimes (SXS) Collaboration