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Assuming for a second that there were a pocket of anti matter somewhere sufficiently large to form all the type of object we can see forming from normal matter - then one of these objects would be a black hole.

Question is, would there be a difference between an anti matter black hole and a normal matter black hole - in terms of how would the matter/anti-matter make the black hole different, or would they be the same?

I would expect the answer to be that the black hole formed from anti matter would retain the anti-matter properties in such a way that if it was to merge with a black hole at same size formed from normal matter that they would annihilate each other con convert into pure energy - Would that be a correct understanding?

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  • $\begingroup$ Is there any reason to discard the possibility non massive BH could contain both matter and anti-matter? Exactly as our observable universe does. $\endgroup$
    – athena
    Commented May 31, 2023 at 19:48

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That other question mentioned in the question-comments also discussed annihilation of particles and neutralization of electric charge inside the event horizon. In either question, the no-hair theorem trumps all. If GR is the end of the story, particle identity is destroyed by the singularity. Even if post-GR theories of gravity rescue the Universe from the creation of singularities, it doesn't matter because the form of the mass-energy inside the event horizon doesn't matter to the outside world.

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  • $\begingroup$ Still not exactly what I was looking for in an answer -- I was specifically interested in understanding if anyone had any theory as to what happens inside regardless of whether it was observable to the outside (which I agree that it is not). While that may sound irrelevant, then I have a different follow-up question in mind in which the answer to this question would matter significantly. $\endgroup$
    – Soren
    Commented Aug 15, 2011 at 18:28
  • $\begingroup$ In GR, particle identity is lost in the singularity. No one knows enough about post GR theories to say what "saturation matter" looks like- it's kind of the ultimate (in the real sense of final) goal to describe the densest possible matter. $\endgroup$
    – Andrew
    Commented Aug 15, 2011 at 18:47
  • $\begingroup$ While particle identity such as electrons, neutrons etc loose identity, then the issue here is whether they also loose their identity beyond matter/antimatter even if on subatomic particles, which seams unreasonable as it would mean something becoming nothing, if it is not even converted into energy -- however I accept this answer as the best understanding given GR, while I was hoping that there was a better post-GR answer that somebody could come up with. $\endgroup$
    – Soren
    Commented Aug 15, 2011 at 21:05
  • $\begingroup$ xkcd.com/171 $\endgroup$
    – Andrew
    Commented Aug 15, 2011 at 21:43
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    $\begingroup$ @JerrySchirmer: I don't understand what Andrew means by "charge neutralization" or its relevance to the present question. Charge is conserved. Antimatter can have any electrical charge, including zero. As you've pointed out, electric charge is a variable that no-hair theorems do not say is undetectable. Charge is not the only thing that differs between particles and antiparticles. Antineutrinos differ from neutrinos, for example. What's relevant here is that black holes "forget" the quantum numbers such as lepton number of the infalling matter. $\endgroup$
    – user4552
    Commented May 12, 2013 at 20:28
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No, the merger of a matter-formed blackhole with an antimatter-formed blackhole would not cause the blackholes to be converted into energy -- putting aside the mutual annihilation of accreting matter/anti-matter outside the event horizon, which certainly would cause a lot of fireworks.

Event horizons are like Vegas, what happens there stays unknown to the outside world. The energy of matter/antimatter collisions cannot escape the horizon. Remember that the event horizon isn't a physical surface, like an egg shell, it's just a "point of no return." As two black holes "merge" they just have overlapping regions. If, an antimatter particle originating from one region happens to meet its complement inside another, it's no different than if you had such a collision by happenstance inside a single blackhole; if you had an entire antimatter-formed black hole's worth of particles that would certainly make for a large number of such annihilations, but the conversion of mass to energy inside the event horizon would be unknowable to an external observer.

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Since a black hole is essentially an expression of a sufficiently deep curvature of space-time in general relativity, and gravity from anti-matter is expected to be the same as the gravity from matter, I would say there is no difference.

As a practical matter, I would expect that it would be very unlikely that absolutely all the anti-matter would get sucked into the black hole. All instances that have been investigated involve the formation of relativistic jets of matter expelled from the poles of the accretion disk. These jets would give themselves away as antimatter when they ran into normal matter and the high energy photons (gamma rays) characteristic of matter-antimatter annihilation would be emitted.

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  • $\begingroup$ Good answer, but not specifically what I was looking for (my fault and I will update the question) -- I was specifically looking for interpretation of what happens to the anti-matter which is sucked into the black hole -- does it cease to be anti-matter or is there some other interpretation as how it would stack up against a back hole sucking in normal matter? $\endgroup$
    – Soren
    Commented Aug 11, 2011 at 2:33
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According to Thorne (Black Holes and Time Warps) all matter that approaches the black hole singularity is reduced to a common degenerate form - matter and anti-matter alike. The way I interpret it, matter ceases to retain any resemblance to what existed outside the black hole. The attributes that distinguish matter and anti-matter are stripped away.

According to astronomer's newest observations and the belief that black holes may play a fundamental role in the evolution of galaxies I wonder now if this may be leading towards an explanation of the broken symmetry after the big bang. Perhaps black holes could explain where all this antimatter has been trapped - hidden behind the horizon. Is that possible, and if so how and why?

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To put it simply, 1 black hole + 1 antimatter black hole of the EXACT same size would result in the release of more energy than anyone on earth could possibly comprehend. If matter + antimatter = annihilation, then doing it on a large scale would just mean releasing more energy.

To put it even more simply, being a "black hole" simply means it's achieved enough mass to collapse at an atomic scale under its own gravity. It's still made up of whatever went into it.

In conclusion, 1 particle of matter + 1 particle of antimatter (times however many particles you used) = 2 gamma rays (times # of starting particles)

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    $\begingroup$ This is incorrect, for the reasons stated in the other answers. $\endgroup$
    – Benjamin Horowitz
    Commented Aug 3, 2012 at 5:16

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