Gravitational waves

propagating spacetime ripple

In theories of quantum gravity, the graviton is the hypothetical elementary particle that mediates the force of gravitational interaction. It is a quantum of gravitational wave energy. There is no complete quantum field theory of gravitons due to the unsolved mathematical problem of renormalization in general relativity. This problem is avoided in string theory, which has the graviton as a massless state of a fundamental string, but that theory has not made sufficient progress.

system consisting of two black holes orbiting each other

type of stellar collision

random gravitational-wave signal potentially detectable by gravitational wave experiments