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Black Holes and the Event Horizon?

  1. Oct 19, 2006 #1

    TDS

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    My questions are these: When a Black Hole is detected, Is it found by its Event Horizon? Is the Event Horizon located in relation to the stars equitorial plane? If I were to approach a Black Hole from its "North Pole" or "South Pole", would I be affected by its Event Horizon?
     
  2. jcsd
  3. Oct 19, 2006 #2
    The event horizon is a sphere surrounding the center of a black hole.
     
  4. Oct 19, 2006 #3

    George Jones

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    Consider the region of spacetime from which it possible for a photon to escape to (future null) infinity. Now consider he complement of this region, i.e., a region of spacetime from which it is not possible for a photon to escape to infinity. This latter region is the black hole region.

    The boundary between the two regions is the event horizon.

    Unfortunately, there are no warning makers that tell you when you cross an event horizon.
     
  5. Oct 19, 2006 #4

    TDS

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    I had not though about the Event Horizon as being spherical! What a concept!

    Would you happen to know of any books or links where I could read more about this!


     
  6. Oct 19, 2006 #5

    TDS

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    So is it safe to say that the Accretion Disk and the Event Horizon are two different things? I had thought that they were the same thing.


     
  7. Oct 19, 2006 #6

    George Jones

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    In my opinion, this book has the best popular-level treatrment of black holes - I can't recommend it highly enough. Great diagrams.
     
  8. Oct 19, 2006 #7

    George Jones

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    Yes, they are different. The accretion disk lies outside the event horizon.

    Sorry, gotta run! I'll try and add some more details tonight.

    Are asking about evidence for an event horizon that can be seen from afar, or evidence as you cross an event horizon?
     
  9. Oct 19, 2006 #8

    TDS

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    George Jones,

    Thanks for this link! My home library has just gained mass!:biggrin:
    If you have more links or suggestions, feel free to send them to me. The more that I learn - the better I will be!


     
  10. Oct 19, 2006 #9

    TDS

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    Any information that you can provide on both will be more than I have at the moment. Basically what I am trying to understand is this; everytime you see a depiction of a Black Hole, you see a ring of "light" that signifies the event horizon around the Black Hole. And in the same breath the narrator starts talking about the accretion disk. I would like to understand the difference. As for your questions - both.



     
  11. Oct 19, 2006 #10

    pervect

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  12. Oct 19, 2006 #11
    Accretion disk are swirling matters being pulled into the black hole. They glow as the result of being heated up by the friction. The event horizon is a spherical boundary which you can't escape once you get passed. You can't see the event horizon, at least not directly. If you have a black hole sitting around a region with not much matter, there will be no accretion disk. But the event horizon is always there.
     
  13. Oct 20, 2006 #12

    TDS

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    @pervect,

    Thanks for the book link! There goes the mass of my bookshelf again!

    @yenchin,

    Thanks for clearing up my questions about the Event Horizon and the Accretion Disk!

    Now for the really big question. Since the Event Horizon is spherical, is the Accretion Disk also spherical or does it exhist along the equitorial plane of the Black Hole?
     
  14. Oct 20, 2006 #13

    George Jones

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    No, the acretion disk is a disk, i.e, it lies in a plane, for roughly the same reason that the orbits of all the planets lie in a plane.

    For accretions disks, I can do no better than to quote from Gravity: An Introduction to Einstein's General Relativity, by James Hartle.

     
  15. Oct 20, 2006 #14

    TDS

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    First let me say THANKS to all that has posted answers to my questions on this thread!!!:biggrin:

    I have received more answers in two days on this site than I did in my first semester of Astronomy! This is a good thing for you folks, a sad thing for the school that I went to.

    Now for another question.

    Would it be possible to observe a Black Hole so long as the probe stayed outside of the Accretion Disk?

    I know that the only thing that could actually be observed would be the Accretion Disk unless the probe had a device to detect Hawking Radiation.
     
  16. Oct 20, 2006 #15
    Yes. If you stay sufficiently far away at a safe distance, you can observe the accretion disk. Hawking radiation is too weak to be detected as it is many times weaker than the microwave background radiation.
     
  17. Oct 21, 2006 #16
  18. Oct 22, 2006 #17

    TDS

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    @chronon,

    My thanks goes out to you as well! If this keeps up I shall need to get another bookshelf!:biggrin:


     
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