It also depends on the starting point. If both the gravity wave and the light start in the middle of a star or even just inside a shell of an exploding star, or, in case of black holes, inside a cloud of matter that surrounds the hole waiting to be sucked in, there is more than enough matter to delay the light.
It also depends on the starting point. If both the gravity wave and the light start in the middle of a star or even just inside a shell of an exploding star, or, in case of black holes, inside a cloud of matter that surrounds the hole waiting to be sucked in, there is more than enough matter to delay the light.