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B Do black holes radiate antimatter?

  1. Jun 26, 2017 #1
    I'm wondering if black holes radiate antimatter as well as matter? If they radiate antimatter in equal amounts to matter, then would it all cancel out?
     
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  3. Jun 26, 2017 #2

    Drakkith

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    My understanding was that they could radiate any type of particle, including anti-particles. The smaller the black hole, the larger the average mass of the radiated particles, so you won't see antimatter being radiated by any stellar mass black holes or larger.

    Would what cancel out? The amount of matter vs antimatter?
     
  4. Jun 26, 2017 #3
    My understanding is that EM radiation (aka photons) do not have an antiphoton equivalent.
    Photons are photons regardless of the state of matter that originated them.
     
  5. Jun 26, 2017 #4
    I suppose that black holes do radiate both matter and antimatter in equal amounts and that they do annihilate into photons leaving for the most part photons that radiate away from the BH. Is this right?
     
  6. Jun 26, 2017 #5

    Drakkith

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    I'm not sure. I don't see right away why all of the particles and antiparticles are annihilating. They'd have to collide first. I'd expect to see some portion escape without colliding with its antiparticle. But, like I said, I don't really know.
     
  7. Jun 27, 2017 #6
    I'd be curious to know at what mass a black hole becomes significantly likely to emit an positron.
     
  8. Jul 1, 2017 #7
    As I understand it, there are virtual particle pairs formed just outside the BH horizon. Positive energy particles radiate out, and "negative energy" particles fall into the BH and reduce its total energy. My question is what's the difference between antimatter and negative energy particles? Antimatter is sometimes described as having negative mass or as traveling negatively through time. What constant gets the negative sign in negative energy particles?
     
  9. Jul 1, 2017 #8
    I'm not well educated on black holes. The "negative energy particles" are not real. I am more familiar with vacancies and holes which are also not real. For example we can put boron into a silicon crystal lattice. The "hole" is a point on the lattice missing an electron. Engineers talk about "holes" as if they were a thing and that works well for designing integrated circuits. A "hole" is not the same thing as an anti-electron or positron. Current really does flow through circuits when electrons and holes meet and annihilate each other.

    My impression was that particles tunnel out of the event horizon. In order to escape from near the event horizon a particle must have near light speed velocity. So the particles do not escape they fall right back in. All types of particles radiate energy as they fall into a black holes.

    The black hole losses mass from evaporation because energy and mass are interchangeable. Escaping photons carry away energy. Shining a light at a black hole will increase its mass.
     
  10. Jul 2, 2017 #9

    Nugatory

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    Hawking radiation will contain both matter and antimatter in equal amounts, and it does not cancel out, because the particles and antiparticles both have positive mass-energy.

    However, for any currently existing stellar-mass black hole the "equal amounts" are both zero, because the energy available for Hawking radiation is so small that only very long-wavelength low-energy photons have any probability of emission.
     
  11. Jul 2, 2017 #10
    The probability of tunneling events is not zero. So, for example, the hydrogen atoms in your little toe could tunnel over and fuse with each other. That would result in a decent sized explosion. The odds are just so low that you might as well not worry about this problem. But the probability is greater than zero.

    All of the mass/energy in a black hole is available. Odds of a tunneling event drop exponentially when you involve multiple particles in the event. (really exponential not the figure of speech). Also the distance has a strong effect on tunneling event probability. So the likelihood that an alpha particle tunnels out of a plutonium nucleus is much higher than the probability of a hydrogen nucleus tunneling into an adjacent atom. In stellar mass black hole the likelihood of a tunneling event crossing the event horizon is quite low despite the large amount of available mass. Our stellar mass black holes will be adsorbing cosmic background radiation faster than they will be emitting photons. They will grow until the universe and nearby space goes through a heat death.

    In normal conversation it is probably best to avoid making a distinction between "not happening, zero", "so slow it takes a ludicrously long time to notice an effect", or "happening well below the background noise level". But this is a physics forum so I think the details are worthy of discussion.
     
  12. Jul 2, 2017 #11

    mfb

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    That is a pop-science myth. It is not what actually happens.
    That is completely wrong.

    All the black holes we know are so massive (3+ solar masses) that they only emit electromagnetic radiation with extremely low frequencies. There is a theoretical chance that they emit massive particles, but the probability that any black hole in the observable ever did that in the history of the universe is below 0.000000001%, so why bother.
    At 10-7 solar masses we get a few neutrinos in addition.
    At 10-16 solar masses or 1014 kg we get some electrons and positrons - in equal amounts for an uncharged black hole. A black hole with this mass has a Schwarzschild radius of just a few hundred femtometers, smaller than an atom.
    At 1011 kg we also get pions as the lightest hadrons. A black hole with this mass is smaller than a proton and emits Hawking radiation at a power of a few GW. It still has a lifetime of about a billion years.

    Everything emitted will just fly away, matter and antimatter fly away in exactly the same way.
     
  13. Jul 2, 2017 #12
    Why would it fly away instead of orbiting? How would a charged particle avoid interacting with nearby charged particles that are orbiting?
     
  14. Jul 2, 2017 #13

    mfb

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    Hawking radiation is emitted. It flies away because otherwise it wouldn't be Hawking radiation. There is also no process that would lead to orbiting particles.
    That is a possible process if there is something orbiting the black hole.
     
  15. Jul 2, 2017 #14
    I am missing something here. I thought the entire galaxy is orbiting a black hole. Radiation from accretion disks is emitted by particles orbiting.
     
  16. Jul 2, 2017 #15

    mfb

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    There is a central black hole, and a few stars are directly orbiting this central black hole, but the mass of the black hole is tiny compared to the total mass of the galaxy. Most parts of the galaxy wouldn't even notice if the central black hole wouldn't be there.

    This has nothing to do with Hawking radiation, where things are emitted from the black hole.
    This has nothing to do with Hawking radiation either.
     
  17. Jul 2, 2017 #16
    A particles position is uncertain. Sometimes it finds itself in various places. A particle that was inside the event horizon and finds itself outside the event horizon is not going to behave any differently than other particles outside of the event horizon. If other particles near the black hole are orbiting and gradually making their way into the hole via friction then one of Hawking's particles does the same. We would only see Hawking particles escaping when we see other orbiting particles escaping.

    Contrast with an alpha particle in radium. When the tunneling event happens there are two nuclei (radon and helium) with positive charges close enough to each other for electric repulsion but too far for nuclear binding. The nuclei they fly apart with high velocity. An alpha particle a short distance from a black hole will not feel a strong repulsion. There is no energy released by traveling up a gravity well.
     
  18. Jul 2, 2017 #17

    mfb

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    There is no such thing.

    Hawking radiation is created outside.
    No. They travel in different directions, and at different speeds for massive particles. In addition, Hawking radiation for massive black holes is exclusively electromagnetic radiation, while the particles in the accretion disk are massive - there are no stable orbits for light.
     
  19. Jul 2, 2017 #18
    I need some help understanding this negative energy going into the BH. I'm thinking that the Hawking radiation is similar to the Unruh radiation, both being produced by accelerated reference frames. Does Unruh radiation produce negative energy "particles"? What is negative energy? Isn't this the stuff needed to keep worm holes open for which we really have no hope of producing? Why not?
     
  20. Jul 3, 2017 #19

    mfb

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    There is no such thing.
    No.
    It is unclear if things can have negative energy at all. Probably not.
     
  21. Jul 7, 2017 #20
    What about gravity? Doesn't gravity have "negative energy"? Would gravitons be particles with negative energy?
     
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