# Black hole vs Black hole

by Chemist@
Tags: black, hole
 P: 69 What happens when a black hole devours another black hole? The bigger eats the smaller and increases in mass and size? What happens with the singularities?
 P: 44 The black holes undergo inspiral motion: their orbit decays through gravity wave emission, and then they are thought to merge. The merging phase is very brief (few miliseconds), produces another black hole, and understood primarily through numerical simulations.
 Mentor P: 11,997 I think Stargazer is correct. The two would merge and exist as one black hole with a mass equal to the mass of the two prior to merger.
 P: 390 Black hole vs Black hole The end result should generally be a Kerr or Newman black hole. So are the initial black holes (a Schwarzschild or Nordström black hole is the limiting case of a Kerr or Newman black hole of no diametre.) But what happens to the topology of the ring singularities inside the common event horizon during the merger? Can a ring singularity be, for example, snapped into a singularity with loose ends? Or what happens, geometrically, on a triple junction of two loops of singularities after the two rings have touched?
P: 69
 Quote by stargazer3 The black holes undergo inspiral motion: their orbit decays through gravity wave emission, and then they are thought to merge. The merging phase is very brief (few miliseconds), produces another black hole, and understood primarily through numerical simulations.

"But what happens to the topology of the ring singularities inside the common event horizon during the merger? Can a ring singularity be, for example, snapped into a singularity with loose ends? Or what happens, geometrically, on a triple junction of two loops of singularities after the two rings have touched? "

Nicely formulated. This would be the second question.
P: 2,193
 Quote by snorkack But what happens to the topology of the ring singularities inside the common event horizon during the merger? Can a ring singularity be, for example, snapped into a singularity with loose ends? Or what happens, geometrically, on a triple junction of two loops of singularities after the two rings have touched?
This is a good question, but one I suspect noone is able to answer at the moment. Numerical simulations like the one listed above use a variety of techniques, but they all get rid of the singularities. One way to do this is to simply not simulate anything inside the event horizon, since the details are irrelevant to the goal of the simulation.
 P: 215 But what about a black hole colliding with an antimatter black hole? Does antimatter-matter annihilation destroy the mass of both? If yes the collision product should cease being a black hole and remnants would stream out, But wait! Would the radiation produced by annihilation gravitate as much as the mass would? Can we have a radiation only black hole? But wait wait! Because time is frozen at the event horizons maybe the mater and antimatter will never come in contact in finite time. Then it would be no different than two matter black holes merging. It makes my head hurt to think of such things.
PF Gold
P: 6,486
 Quote by anorlunda ... Because time is frozen at the event horizons maybe the mater and antimatter will never come in contact in finite time
Whoever told you that misinformed you. That just how it looks to an outside observer, NOT to things falling in, which don't even know the EH is there.
 P: 215 Whoops, allow me to rephrase. But wait wait! Because time is frozen at the event horizons maybe to an outside observer the mater and antimatter will never come in contact in finite time. No annihilation would occur in finite time as seen by an external observer. Then it would be no different than two matter black holes merging.
 P: 1,857 An antimatter star could not form in a matter dominated universe, therefore you cannot have an antimatter blackhole to encounter a matter blackhole.
 Sci Advisor PF Gold P: 9,484 Since the matter inside a black hole is crushed to a singularity [in classical theory], it appears the collapsed matter would not retain any of its precollapse properties besides gravity. Another issue would be any hypothetical anti gravity effects between an antimatter and normal matter black hole. How could they merge if they repulse each other? If both possess normal gravity, the singularities would not come into contact until they were inside the event horizon. Given nothing can escape the event horizon, any energy released would be trapped inside the event horizon. On that basis it appears antimatter/matter black hole mergers [if possible] would be indistinguishable from a merger between two matter black holes.
 P: 8 I understand why BH orbits decay generating gravitational waves and I agree that from an external observer the two BH seem to merge into one, but I think that from the BH point of view this does not happen. What I mean is that the bigger BH inglobates the smaller one, but there should remain a tiny (getting ever smaller) space of regular space between the two horizon surfaces. Lets say that we have two BH with horizons that have radii of 1 meter each. If the two BH are distant their horizons are spherical, because in every point of the space surrounding the BH the gravitational effect of the second BH are very small. Now think of drawing a straight line between the two singularities as the two BHs get closer. Don't stop the line at the singularities but extend it so that exits from the other side of each horizons (the two BHs approach each other in a spiral motion, and the direction of the line changes, but as external observers we can always draw a line joining the two singularities and extending it past them). In any given moment of time particles that are on the external portion of the line (the portion that is not between the black holes) feel the gravitational force of the nearest blackhole AND the other BH, this mean that they need an higher escape speed and the final effect is that the event horizon of the nearest BH further extends in space in the direction opposite to the one by which the second blackhole is approaching. Particles in the internal portion of the line feel the opposite effect: because the gravity from the more distant black hole is partially contributing to pull them away from the nearest one: their escape velocity is reduced, so an external observer should see the horizon receding. A particle that is exactly at the midpoint between the blackholes (since the two have the same size) should always be able to escape with a trajectory perpendicular to the line, no matter which is the distance between the two BHs. The singularities will always approach eachother, but I think they will never really merge, the horizons between the BHs will recede and get flatter almost to perfect circular sections and there should always be some regular space between them. If the two BH have sufficiently different masses the smaller BH will be swallowed by the bigger one, but still they will not merge: there will always be a small region of 'regular' space surrounding the event horizon of the smaller BH. The small blackhole will eventually evaporate into the big one, but this is an extremely long process.
 Mentor P: 11,997 Remind me which point of view the BH is?