Conceptually, gravitational waves are required out of respect for the speed limit. As one black hole orbits another, the curves in the shape of spacetime must drag around with them, but the shape of spacetime cannot acclimate instantaneously, since that would require propagation of information—about the motion of the holes—faster than the speed of light. As the black holes move, the curves shift and adjust, and those changes wave outward incrementally and at the speed of light, carrying energy away from the violent astrophysical motions.
