[ELI5] if a (relatively) small black hole is orbiting a more massive black hole, as they eventually merge, would the matter be drawn back out of the singularity of the smaller?

Question

I understand that they consume matter and grow, and that black holes merge to form larger ones. But I’m curious if scientist know whether or not this takes place bit by bit, or whether because the matter can’t escape the singularity of the smaller one, it would be a case of the entire thing being eaten up all at once?

If the latter is the case, would this happen in an instant with a reaction, or just a slow process as it all gets enveloped?

To clarify: I’m aware that in some cases, ultramassive black holes have other black holes orbiting them, because I watched the kurzgesagt video on it, but that’s the extent of my knowledge

Many thanks

In: Planetary Science

Answer 1

Relevant fun fact: when two black holes merge, the diameter of the resulting black hole is the _sum_ of the individual diameters. So a 1 km and a 2 km black hole form a 3 km one. That is very different from merging water drops where the _volumes_ add up, not the diameters!

So they are already merged when they would barely touch. But it’s not as simple as staying spherical until they touch, then suddenly popping into a larger sphere. Instead they keep circling each other and each forms a elongated shape. After the merger they will still have lots of rotational energy left over, so the final sphere is wider at the equator.

Disclaimer: by diameter, shape and all that I speak about the event horizon. The singularities themselves are essentially just punctures in space.