Thanks, that's helpful. It's hard to get my head around the idea that an event so massive can be over so "quickly", without any residual longer-lasting effects.
Well it sounds like a massive ripple in the fabric of reality which passes by us in a fraction of a second, never to be seen again.
So from my non-physicist point of view, no it doesnt seem like a very long lasting effect, relative to us at least. Thanks for the snark though.
There's a theorem that black holes have "no hair": two black holes of the same mass, charge and angular momentum are indistinguishable. So the merge must happen instantaneously: if the combined black hole were "sloshing" afterwards that would violate that theorem.
