# Blackhole and Anti-Blackhole Annihilation

Ok I am wondering what would happen if an anti-black hole collided with a black hole of the same mass. Would they annihilate and release energy or would it become a more massive or less massive black hole?

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mfb
Mentor
What do you mean with "anti-black hole"?
The theoretic solution of white holes? They would need a negative mass, and repel masses, so I doubt that they could merge with a black hole.
A black hole, made from antimatter? This does not matter (;)), only the energy content is relevant. They would behave like regular black holes, and if they hit another black hole they merge to one bigger black hole.

bcrowell
Staff Emeritus
Gold Member
There is no standard meaning of your term "anti-black hole."

In particle physics, "anti-" means something having the opposite charge, but that doesn't sound like what you mean.

It's conceivable that you might mean an analogy of the form (compression wave of sound):(rarefaction wave of sound)::(black hole):(anti-black hole). In this case, the anti-black hole isn't a solution to the Einstein field equations, which are nonlinear.

There is the theoretical possibility of a white hole, but a white hole is not a physical object like the one you seem to have in mind. It can't be formed by gravitational collapse.

They would need a negative mass, and repel masses, so I doubt that they could merge with a black hole.
This is a little subtle. I originally posted that it was not true that they had negative mass. Actually I think it's more complex than that. On the Penrose diagram for a maximally extended Schwarzschild metric, you have a whole separate universe in which the definition of energy is negated. It's not obvious to me how to apply that to a universe in which both a black hole and a white hole are accessible from the same external space.

[EDIT] Having studied up on this a little more, I think the answer is that white holes do not have negative mass, and they attract rather than repel test particles.

The Schwarzschild metric with negative mass is nothing like a black hole or white hole. It's an unstable naked singularity: http://arxiv.org/abs/gr-qc/0604021

The WP article http://en.wikipedia.org/wiki/White_hole states that a white hole attracts matter rather than repelling it. This makes sense, e.g., because we expect the ADM mass to be conserved in the maximally extended Schwarzschild spacetime, which consists of a white hole followed by a black hole at later times.

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I'm sorry I meant a anti-matter black hole. I was using the anti term like used in anti-matter or anti-galaxy.

bcrowell
Staff Emeritus
Gold Member
I'm sorry I meant a anti-matter black hole. I was using the anti term like used in anti-matter or anti-galaxy.
Then if it's electrically neutral, the anti-black hole is the same object as the black hole.

Chronos
Gold Member
A black hole is believed to possess only 3 fundamental properties - mass, charge and spin. None of these properties appear to have a matter - anti matter bias. Keep in mind that matter is utterly disassembled by a black hole, not just atoms, but, all of their constitues particles. The type of matter that enters the event horizon does not appear to be of any consequence.

And these properties reside at or outside the event horizon?

bcrowell
Staff Emeritus