General relativity holds true, even under the extreme conditions of colliding black holes.
In 2015, the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) saw the first evidence of gravitational waves, which had been created by two merging black holes. Walter Del Pozzo at the University of Birmingham, UK, and his colleagues on the LIGO collaboration and its European partner, the Virgo collaboration, compared the signal with those predicted by simulations based on general relativity. The teams found that the observations matched the predictions to a high degree, as they had in previous tests under much weaker gravitational fields. This was the first direct test of Einstein's theory of general relativity under such extreme space-time warping and fast-moving conditions.
With planned boosts to the LIGO detectors' sensitivity, future observations could be used to test other theories of gravity and hypothesized alternatives to black holes, say the authors.