In GR theory the speed of light and gravity are about the same. So how can we see the effects of gravity by large bodies on galaxies in our universe and not observe the light from these large bodies?
One of the fascinating new ideas about gravity is that, unlike light, it leaks out of our universe and other universes, dissipating its felt effects on us. That notion is invoked as a way to explain why gravity is so much weaker than the other known forces in nature.