Let s say we have two black holes, one 20 solar masses and the other 50 solar masses, and they get close enough and merge. In the process, they convert a solar mass or two into gravitational waves, which radiate off into the distance.Let me restate that, to emphasize what I think is really weird: A solar mass or two that is inside the event horizon got converted to energy and radiated outside the event horizon.E=mc^2. That part doesn t bother me. It s the inside the event horizon to outside the event horizon part that bothers me. Can someone ELI5 how that is possible? (Or even ELI20 with an undergrad in physics.)