What is the entropy change of the univers when two massive b

Solution

Before merging, the two black holes are less gravitationally bound systems. When they were coalesce, they become more bounded system or(more orderly arranged system). So, the entropy decreases. However, the disturbance created by the collision ( gravitational waves ) will makethe other objects to less orderly arranged. And the net result is to increase the entropy of universe or to remain constant.