Hawking radiation

Discussion in 'Physics' started by hp1729, Feb 13, 2016.

  1. hp1729

    Thread Starter Well-Known Member

    Nov 23, 2015
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    Help me understand this please. Hawking radiation comes from the evaporation of a black hole. But a black hole has so much gravity that nothing can escape??? Does Hawking radiation come from the event horizon, before the extreme gravity that sucks in everything? If it comes from the event horizon then does it only happen in feeding black holes, not dying black holes???

    Where am I confusing myself? If Hawking got the idea from his trip to Russia in 1973 how does he get to tie his name to it? The concept was not originally his was it?

    (edited to add ...)
    Hawking radiation is electromagnetic radiation of "trans-Planckian" wavelength, shorter than the Planck length???
     
    Last edited: Feb 13, 2016
  2. Wendy

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    Actually it was his discovery. You can not not read and expect to have the answers.

    It has to do with Quantum Foam, google Casmire effect and small event horizon sizes.

    Another bit of strangeness the universe offers.
     
  3. hp1729

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    Jacob Bekenstein didn't have anything to do with the idea?
     
  4. crutschow

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    In the quantum vacuum, particles and their associated anti-particles are constantly being formed and then recombine a short instant later. When this occurs exactly at the event horizon there's a finite chance the one particle could escape and the other be sucked into the black hole, leaving some net radiation outside the black hole that can escape.
    Hawking was the first to propose that (on his own as far as I know) so this radiation from the event horizon is called Hawking Radiation.
     
  5. hp1729

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    ????Must be a different radiation. I thought the subject had to do with the decay of black holes. Yes, what you speak of is expected, certainly. Is this hawking radiation? This radiation did not start with Hawking, did it?
     
  6. Wendy

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    The theory did indeed.
     
  7. Glenn Holland

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    One simple form of radiation from a black hole would be gravity waves.

    Gravity waves would transmit energy away from the hole and this is discussed in the recent discovery at Caltech.
     
  8. joeyd999

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    AFAIK, gravity waves do not contribute to the decay of black holes. Again, AFAIK, only Hawking radiation can do this.
     
  9. Glenn Holland

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    Where would the particles originate? Would they be from within the horizon?

    In order for the black hole to decay, mass and/or energy must be removed from it and transported far enough that it cannot be recaptured.
     
  10. joeyd999

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    There are virtual particles and anti-particles formed at the horizon. From what I understand, one of the pair may get trapped within the horizon, while the other escapes, turning both into real particles. I believe there is a mechanism where there is a preference for anti-particles to get trapped. Due to CPT symmetry, an anti-particle falling into a black hole is the same as a particle escaping from it (time/parity reversal). So, radiation is emitted (as the particle) and mass is reduced (by the anti-particle).

    The overall effect is equivalent to a particle escaping the singularity of the black hole.
     
    Last edited: Feb 13, 2016
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  11. Wendy

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    All black holes radiate particles, but large masses slow the process down a lot. As the mass of a BH decreases you can have a run away effect, where the final event is an explosion. Most cases it will take billions of years or longer for a large BH to dissipate.

    Also, due to Hawking radiation, a BH can be referred to as having a temperature. It is a function of mass, the more massive the colder it shows. If the temperature of the BH is colder than the universal background radiation it is absorbing more energy than it is giving off (and growing ever so slightly). If the reverse is true the BH is loosing mass ever so slightly.
     
  12. hp1729

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    All radiation must come from the event horizon, right? Since the singularity itself has too high a gravity for "anything" to escape? Then where does Hawking Radiation (that trans-Planckian wavelength stuff) come from? Do we only have a radiating event horizon on feeding black holes, not dying black holes?
    Is Hawking radiation so high in frequency, and thus energy, that it can escape the singularity, thus decaying the singularity?
     
  13. Wendy

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    See post #10. Also post #2.
     
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