Back to cosmology: The biggest mistake people make in viewing the universe is that gravity is a force. It really is time curvature.
In this spacetime curvature, it is time that curves the most. In our area time curves one way in the presence of matter but far out in the universe it curves the other way. We call this an expansion of the universe but it is the effect of space time curvature so galaxies appear to be moving away from each other and not like local spacetime curvature that we call gravity, pulling things closer.
Black holes curve time so much it is a one way trip in which nothing can re emerge since they can not exceed the speed of light. What we call gravity waves are ripples in space time curvature.