• Charged black hole

    From John L.@21:1/5 to All on Sun May 29 17:38:16 2022
    Let's say I start adding electrons to a black hole. As more are
    added the black hole starts to develop a charge. The charge increases
    as the electrons are added. At some point, will the electrons stop
    being drawn into the black hole?

    [[Mod. note --

    As soon as the BH has any negative charge, there will be an electrostatic repulsion between the BH and any nearby electrons. There's a limit to
    how much charge you can put on a black hole and still have it be a black
    hole: charged black holes always have |Q| < M in dimensionless units, i.e.,
    a body with |Q| > M in dimensionless units isn't a black hole -- it's either
    a solid object or it has a naked singularity at r=0.

    I think (but am not quite sure) that |q|/m for electrons is large enough
    that the electrostatic repulsion would be > the gravitational attraction
    long before the BH charg reached |Q| = M in dimensionless units. I.e.,
    I think (but am not quite sure) that the answer to your question is "yes".

    See
    https://en.wikipedia.org/wiki/Reissner-Nordstrom
    for more on the spacetime geometry of a charged black hole.

    See Misner, Thorne, and Wheeler exercise 31.8 for more on the author's question, and for why |Q| > M isn't a black hole any more.
    -- jt]]

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