Gravity is supposed to propogate at the speed of light; but is there any way to slow it down "in a medium" as light can be? Are gravitons (theoretically) supposed to be emitted and absorbed by masses the way photons are by atoms? If so, could something like a star cluster act in the same way a medium does for light to "slow down" gravity (i.e. take a gravitational signal, with all the absorbing and reemitting, longer to travel from one side of the cluster to the other than if no masses were present)? Or am I completely off here?