Has there ever been a paper that describes what happens in the space between blackholes just before they merge? What I mean is that last few seconds or fractions of a second before event horizons combine and whatever happens inside happens. It seems to me that with gavitational fields being that strong and with the way they seem to work around blackholes at those distances, that there would or could be some phenomena happening in there that could be discerned and described mathematically even if we can’t observe it directly.
This is a question I asked myself too many times. Every time I read an article about black hole collisions, and they mention various phenomena occurring, I wonder what the heck happens to the spacetime fabric there.
Besides approximations, there are many numerical simulations, naturally. Here is one article with pictures of the moment of merger between two black holes.
There is this bit with professor Brian Cox talking to Joe Rogan about the first black holes that merged and were detected.
Cox tells us that the black holes were spiraling in towards each other at around 1/3 the speed of light and then, in the last tenth of a second, accelerated to 2/3 the speed of light. The moment of collision released, just for an instant, 50x the energy of all stars in the universe.
Wrap your head around that. 
Heh! You specifically should, I think😉 UY Scuti
DPRK, thank you, that was an interesting paper, but not quite what I was looking for. (Still, I found it interesting anyway)
I’m curious about the spacetime between the objects though.
Whats happening? Are wormholes being created and destroyed? Extra dimensions being unfurled and crushed back down? Miniblackholes composed of pure spacetime and gravity with no “mass” spawned and reabsorbed? Whole universes in the span of a planck unit brought into existence and entropic death and ultimately destroyed somehow?
What’s going on there is in fact very complicated, but it’s not that complicated. The curvature is getting very crumpled, and it was only 10 or 15 years ago that we even figured out a way to program our computers such that they could handle the problem, but the topology of space outside of the event horizon(s) remains trivial: No wormholes, no virtual black holes, no change of dimension, certainly no new universes. Inside the horizons, all bets are off, but anything that happens there can’t matter.
Solving this computational problem, incidentally, was one of the necessary steps to detecting gravitational waves. Gravitational wave detection is mostly done via template matching, which means you generate a bunch of waveforms that you think could be present, and then compare what you’re getting from your instrument to each of them. Most of the gravitational waves that we have a reasonable hope of detecting come from merging black holes, so we needed to be able to fully model those mergers.
Aw…dang it…oh well, I asked. Still, so much for anihilative time travel or proving the one electron universe to actually be true despite it being a one off speculative thought not meant to be taken seriously
It occurred to me…
When you take the traditional description of gravity as being like a bowling ball on a trampoline…the dip being the gravity…and extend that to two bowling balls, between the two dips are a peak. wouldn’t that peak describe…anti-gravity?
The peak describes that objects between the holes would fall toward one or the other depending on which side of the peak they’re on. If you stand on that “peak” and look something like perpendicularly to the line between the black holes, it’s still uphill. It’s more of a saddle shape, not a peak.
Further, if you take the rubber sheet analogy as far as it can go (which is still somewhat limited by it being 2-dimensonal instead of 3+1-dimensional), peaks and valleys actually end up having the same effect.
I really need to re-make my visual props for this and do some YouTube videos, or something.