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Thread: What is the limit for the charge of a charged black hole and how is it calculated?

  1. #1 What is the limit for the charge of a charged black hole and how is it calculated? 
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    I could only find one reference to this subject .


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    If I'm not mistaken, it had been calculated using the Reissner–NordstrŲm metric.


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    Quote Originally Posted by Neverfly View Post
    If I'm not mistaken, it had been calculated using the Reissner–NordstrŲm metric.
    Most probably , but how?
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    Quote Originally Posted by xyzt View Post
    Most probably , but how?
    Good question. My own ignorance shines, here- You might direct this toward Guitarist.
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    Quote Originally Posted by Neverfly View Post
    Quote Originally Posted by xyzt View Post
    Most probably , but how?
    Good question. My own ignorance shines, here- You might direct this toward Guitarist.
    Here is an attempt. Apparently, according to this:



    Given the definitions for the above means:




    i.e.



    On this other hand, this reference claims a more stringent requirement (no derivation!):

    Last edited by Howard Roark; May 27th, 2013 at 01:14 PM.
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    Quote Originally Posted by xyzt View Post
    On this other hand, this reference claims a more stringent requirement (no derivation!):
    You just made my day.
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  8. #7  
    Malignant Pimple shlunka's Avatar
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    Quote Originally Posted by xyzt View Post
    Quote Originally Posted by Neverfly View Post
    Quote Originally Posted by xyzt View Post
    Most probably , but how?
    Good question. My own ignorance shines, here- You might direct this toward Guitarist.
    Here is an attempt. Apparently, according to this:



    Given the definitions for the above means:




    i.e.



    On this other hand, this reference claims a more stringent requirement (no derivation!):

    Why are you assigning values to the alphabet?
    "MODERATOR NOTE : We don't entertain trolls here, not even in the trash can. Banned." -Markus Hanke
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  9. #8  
    Moderator Moderator Markus Hanke's Avatar
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    Try this :

    Reissner-NordstrÝm solution

    Once the limit is exceeded, the BH turns into a naked singularity, which is possibly non-physical.
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    Quote Originally Posted by Markus Hanke View Post
    Try this :

    Reissner-NordstrÝm solution

    Once the limit is exceeded, the BH turns into a naked singularity, which is possibly non-physical.
    Naked Singularities are VERY DODGY indeed - only detectable with a Mass Detector, and then only if you have a toujgh idea what to look for.

    I seem to remember that a Naked Singularity has NO Event Horizon which is detectable - VEREEEY DODGY INDEED.
    One HELL of a Danger to Interstellar Travel.
    If I wasn't so stupid - I might know what I was doing
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  11. #10  
    mvb
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    Quote Originally Posted by Karakris View Post
    Quote Originally Posted by Markus Hanke View Post
    Try this :

    Reissner-NordstrÝm solution

    Once the limit is exceeded, the BH turns into a naked singularity, which is possibly non-physical.
    Naked Singularities are VERY DODGY indeed - only detectable with a Mass Detector, and then only if you have a toujgh idea what to look for.

    I seem to remember that a Naked Singularity has NO Event Horizon which is detectable - VEREEEY DODGY INDEED.
    One HELL of a Danger to Interstellar Travel.
    I know next to nothing about this, but wouldn't a Black Hole with this much charge be generating Hawking radiation all over the place, mostly with the opposite charge going into the hole? I would expect that the hole's the electric field would even be contributing to the production of Hawking radiation. and in the resulting pair the charge unlike that on the hole would be pulled in and the other member of the pair pushed out. Conceivably that emission could put a practical limit on the amount of charge that you could actually get into a Black Hole, perhaps even a fairly low limit.
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  12. #11  
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    Quote Originally Posted by Markus Hanke View Post
    Try this :

    Reissner-NordstrÝm solution

    Once the limit is exceeded, the BH turns into a naked singularity, which is possibly non-physical.
    Thank you, Markus

    I already used this info in post 5. Can you help me figure out where the more stringent limit, shown here,on page 182, comes from?
    It seems pulled out of nowhere....
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    Quote Originally Posted by mvb View Post

    I know next to nothing about this, but wouldn't a Black Hole with this much charge be generating Hawking radiation all over the place, mostly with the opposite charge going into the hole? I would expect that the hole's the electric field would even be contributing to the production of Hawking radiation. and in the resulting pair the charge unlike that on the hole would be pulled in and the other member of the pair pushed out. Conceivably that emission could put a practical limit on the amount of charge that you could actually get into a Black Hole, perhaps even a fairly low limit.
    That's an interesting thought, mvb.
    In my opinion the entire scenario is purely academic anyway - I would not expect to find any BHs with massive amounts of charge in nature. After all, where is that charge supposed to be coming from ? Given that BHs are the results of collapsing stars ( let's forget about primordial ones for the moment ), I don't see any way how such charge could be picked up; after all, we are not seeing any stars with huge amounts of net electric charge.
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    Brassica oleracea Strange's Avatar
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    I don't know if anyone has worked through the math for Hawking radiation with anything other than a Schwarzschild black hole. Does a charged and/or spinning black hole produce the same result, I wonder? And what if you throw Einstein-Cartan theory into the mix ...
    ei incumbit probatio qui dicit, non qui negat
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    Moderator Moderator Markus Hanke's Avatar
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    Quote Originally Posted by Strange View Post
    I don't know if anyone has worked through the math for Hawking radiation with anything other than a Schwarzschild black hole. Does a charged and/or spinning black hole produce the same result, I wonder? And what if you throw Einstein-Cartan theory into the mix ...
    I don't know about Hawking radiation, but a charged black hole in Einstein-Cartan space-time would not have a singularity at its center; furthermore, it would have not one but two event horizons, and, to top it all of, you could not fall into its centre.

    Isn't geometrodynamics fun !

    P.S. You could also go and embedd your rotating, charged black hole into a 5-dimensional Kaluza Klein space-time with torsion, where one spatial dimension is compactified. Might as well go the whole way
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