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Drop a charge in a neutral black hole

  1. Jun 9, 2010 #1

    What would happen if I sent an electron into a neutral black hole?

    Assume basic (undergraduate) knowledge about black holes. I have studied in some details the Reissner-Nordstrom solution including maximal extension using Kruskal coordinates.

    Thank you!
  2. jcsd
  3. Jun 11, 2010 #2
    No idea ? Even if you don't have a full answer, a qualitative argument would be interesting.
  4. Jun 11, 2010 #3


    Staff: Mentor

  5. Jun 11, 2010 #4
    Outside the blackhole is easier to talk about. It turns out that the electromagnetic field lines act as if the event horizon is a perfect conducting sheet. So as a charge approaches, qualitatively the fields will be like there are two image charges inside: one at the center and one which is moving outwards and will meet the infalling charge at the event horizon.

    Of course there is actually not a big source of charges or anything special at the event horizon. This is just an equivalent way of working with it that scientists have found, if you restrict yourself to asking questions about the region outside of the event horizon.

    I don't know if there is any similar approach to simplify visualization of what is going on inside the event horizon though. Anyone?

    EDIT: Just noticed that this is being discussed in another thread as well.
    The keyword I was having trouble remembering is "membrane paradigm". There are links to more info in that thread, but with the name of the paradigm you can easily look up plenty of stuff yourself if you'd like.
    Last edited: Jun 11, 2010
  6. Jun 11, 2010 #5
    Okay, thanks Justin.
  7. Jun 11, 2010 #6


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    I'm not sure if Justin's comment is in line with this, but I do believe that BHs can hold a charge.

    Drop enough charged matter in, and you've got yourself a BH with a handhold!
  8. Jun 11, 2010 #7
    Yep, they can hold a charge.
    In that discussion above, notice the image charge at the center is there. After the infalling charge meets the horizon, this image charge at the center will equal the charge that fell in ... leaving the blackhole with a net charge.

    The weird part from this is that the solution is almost already symmetric (besides some radiation, etc.) in this outside region by the time the infalling charge hits the horizon! I have trouble understanding this intuitively, and find it fascinating.

    Does anyone know of a similar paradigm for discussing the interior region?
    Last edited: Jun 11, 2010
  9. Jun 11, 2010 #8
    I know of no paradigm for discussing the interior that is not pure conjecture.
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