Do collisions between black holes shed light?

When two black holes spiral around each other and eventually collide, they send gravitational waves, ripples in space and time that can be detected with extremely sensitive instruments on Earth. Because black hole mergers are completely obscure, these events are invisible to telescopes and other light-sensing tools used by astronomers. However, theorists have come up with ideas about how a merger of black holes could produce a light signal by causing nearby material to radiate.

Now, scientists using Caltech's Zwicky Transient Facility (ZTF) located at the Palomar Observatory near San Diego may have pinpointed what this kind of scenario might be. If confirmed, it would be the first known flash of light from a pair of colliding black holes.

Artist's impression of a supermassive black hole at the center of a galaxy

The merger has been identified on May 21, 2019 by two gravitational wave detectors, the National Science Foundation's Laser Interferometer Gravitational-wave Observatory, or LIGO, and the European Virgo detector, in an event called GW190521g. This detection allowed ZTF scientists to search for light signals from the location where the gravitational wave signal originated. These gravitational wave detectors have also detected mergers between dense cosmic objects called neutron stars, and astronomers have identified the light emissions from those collisions.