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Black hole thought experiment

  1. Jun 14, 2015 #1
    Hey so i have a naive question that i always had since i was young, but i never really could find an answer to it.

    Lets say you have a black hole isolated in a vacuum, in a closed system.

    Dark matter is supposed to be a sort of weakly interacting massive particle, which exerts a gravitational pull(?), and undergoes gravitational influence.

    If dark matter is introduced into the system with the black hole, wouldn't the black hole "suck it in" and grow?
     
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  3. Jun 14, 2015 #2

    Orodruin

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    If dark matter falls into a black hole, the black hole grows, just as if normal matter falls into it.
     
  4. Jun 14, 2015 #3
    Ah okay thank you. I've always thought that would be the case. It seems like a simple enough experiment to prove that dark matter is really a particle. Then again, setting up a black hole in a lab is no easy task.

    I guess i also have another follow up question. i believe Dark matter is said to barely interact with other dark matter particles (?), so normally they wouldn't be able to congregate at all. However, they can congregate near gravitational pools (curvatures in space-time)

    Does this mean that dark matter can only congregate in the presence of visible matter?
     
  5. Jun 14, 2015 #4

    Orodruin

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    How do you think this would show that dark matter is a particle?

    Any black hole of lab size would evaporate essentially immediately due to Hawking radiation.
    Also, just that there is a black hole does not mean that a lot of dark matter would fall into it, the dark matter would have to be captured by the black hole first and this is just normal gravitation.

    In fact, it is the other way around. Dark matter structures formed long before matter was cool enough to start forming structures. This plays a key role in our current view of structure formation in the early Universe.
     
  6. Jun 14, 2015 #5

    Ah okay! So dark matter particles DO interact with each other?

    There would be no other DM candidates i'm sure.
     
  7. Jun 14, 2015 #6
    Interesting. Indeed, what happens when dark matter falls into an accretion disk?
    Would it heat up and start to radiate ? Friction might be low with only gravitational interaction.
    Thermal gravitational waves perhaps?
     
  8. Jun 14, 2015 #7

    Orodruin

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    In thermal production of dark matter in the early Universe, it is necessary that dark matter interacts with cross sections of the same order as weak cross sections.
     
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