Question: Is there a specific speed to gravity?

Susan Cartwright answered on 20 May 2020:

Yes there is: it travels at the speed of light. And we actually know that this is true – or at least, we know that gravitational waves, which are just fluctuations in the gravitational field, travel at the speed of light. We know this because in 2017 we were incredibly lucky to observe a pair of neutron stars collide in a relatively nearby galaxy (“only” about 130 million light years away) BOTH in gravitational waves (as the two neutron stars spiral in and collide, they produce a burst of gravitational waves) AND in gamma rays (just after the collision, they produce a rather narrow beam of gamma rays – we were very licky that this beam did not (quite) miss us). The gravitational wave signal and the gamma-ray burst were just a second or so apart, in the right order (GWs before GRs), so – given that both had taken 130 million years to get here – that proves to high precision that both travelled at the same speed.

The original LIGO press release is here: https://www.ligo.caltech.edu/page/press-release-gw170817