What is the approximate speed of gravitational waves traveling through empty space?

Gravitational waves travel through empty space at approximately the speed of light.

General relativity predicts that accelerating massive objects can produce ripples in spacetime. These ripples propagate outward at light speed, carrying changes in the gravitational field. The prediction was confirmed directly on 14 September 2015, when the LIGO detectors observed gravitational waves from two merging black holes in an event called GW150914.

The near-simultaneous observation of gravitational waves and light from the neutron-star merger GW170817 in 2017 placed very tight limits on any difference between gravity’s propagation speed and the speed of light. This was an important test of general relativity and helped constrain alternative theories of gravity.

Gravitational waves are not sound waves moving through air. They are changes in spacetime itself and can travel through vacuum. As they pass Earth, they alternately stretch and squeeze distances by an extraordinarily small amount, which laser interferometers measure.