Can matter or energy escape when two black holes collide?

One would think so but no. Well, actually yes, but only the light that could already potentially escape. Here is a simulation using numerical relativity: https://www.youtube.com/watch? read more

By definition, if matter or light can escape from a point, it is not inside an event horizon. Matter does not escape from merging black holes. Light does not escape from merging black holes. Gravitational waves escape from merging black holes, and have been observed. read more

But if two black holes of Schwarzfield radius r were to collide, the resulting black hole would have a Schwarzfield radius 2r. Since surface area is 4pi*r^2, the resulting black hole would have twice the combined surface area of the two original black holes. And four times the volume. Quite counterintuitive, I agree. read more

Supermassive black holes can collide too. From what we can tell, there's a supermassive black hole at the heart of pretty much every galaxy in the universe. The one in the Milky Way is more than 4.1 million times the mass of the sun, and the one at the heart of Andromeda is thought to be 110 to 230 million times the mass of the sun. read more