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B What if a larger black hole swallows a smaller one?

  1. Dec 27, 2016 #1
    Its thought that nothing can escape a black hole (correct me if I'm wrong) but what happens when a larger black hole eats a smaller one? Could there be a instance in time where matter was torn out of the smaller black hole, past its event horizon and into the bigger one? Thanks!
  2. jcsd
  3. Dec 27, 2016 #2
    No, what happens is that the event horizons merge first, and then quickly things settle down to become one bigger black hole.
    At no point does anything inside an event horizon get sucked outside of it.
    A simulation here:

    However the act of merging causes chaos in material which already is outside the horizons, and one result of this is gravity waves.
    Gravity waves were predicted by general relativity and were confirmed as detected by the LIGO experiment earlier this year
    Last edited: Dec 27, 2016
  4. Dec 27, 2016 #3
    interesting! Thanks!
  5. Dec 27, 2016 #4


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    Gravitational waves (not gravity waves - those are a kind of surface wave in liquids) aren't related to material outside the holes. They would occur even for two otherwise completely isolated black holes. Edit: at least, in general relativity.

    Black holes do accelerate material near them so that it is hot enough to emit in the x-ray spectrum. This is called an accretion disc, and is one of the ways we can hope to see a hole (otherwise it's a black hole on a black background). But it is unrelated to gravitational waves.
    Last edited: Dec 27, 2016
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