1. Subscriberdivegeester
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    18 Aug '09 14:41
    Often illustrated as a dark swirling disc with little depth compared to width; what 3 dimensional shape is a black hole?

    Does it have dimensons? Should it be spherical? Is it mearly gravity creating an optical illusion of shape?
  2. Standard memberPalynka
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    18 Aug '09 15:32
    Originally posted by divegeester
    Often illustrated as a dark swirling disc with little depth compared to width; what 3 dimensional shape is a black hole?

    Does it have dimensons? Should it be spherical? Is it mearly gravity creating an optical illusion of shape?
    Interesting topic. I always thought it 'looked' spherical because of the event horizon...
  3. Germany
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    18 Aug '09 15:41
    I'm not really an expert on general relativity, but a black hole is a singularity isn't it?
  4. Standard memberPalynka
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    18 Aug '09 16:041 edit
    Originally posted by KazetNagorra
    I'm not really an expert on general relativity, but a black hole is a singularity isn't it?
    Accordion to Wikipedia it's not just the singularity, but the "region of space in which the gravitational field is so powerful that nothing, including light, can escape its pull."

    I'm no expert, though. What was on your mind? That a singularity has no volume? (Does it?)
  5. Subscriberdivegeester
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    18 Aug '09 16:161 edit
    Images often depict the bipolar jets:

    http://www.scienceclarified.com/scitech/images/lsbh_0001_0001_0_img0013.jpg

    Here the hole looks flat, but is it actually spherical and just the disc of matter makes it look flat? In either case it clearly has "poles".
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    18 Aug '09 18:28
    Originally posted by divegeester
    Images often depict the bipolar jets:

    http://www.scienceclarified.com/scitech/images/lsbh_0001_0001_0_img0013.jpg

    Here the hole looks flat, but is it actually spherical and just the disc of matter makes it look flat? In either case it clearly has "poles".
    When you see a black hole from a distance, then you don't actually see the black hole itself but only the agregation disc around the hole, and the jets of matter. The actual hole is so small you cannot see it from that distance.

    A black hole, or rather it's event horizon sphere is sperical. Or if it's rotating perhaps flattened a little, I don't think you can see the flattening thou.
  7. Germany
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    18 Aug '09 19:041 edit
    Originally posted by Palynka
    Accordion to Wikipedia it's not just the singularity, but the "[b]region of space in which the gravitational field is so powerful that nothing, including light, can escape its pull."

    I'm no expert, though. What was on your mind? That a singularity has no volume? (Does it?)[/b]
    Well, that is just a matter of definition I guess. You can regard the singularity as the "center" of the black hole, but once again I am no expert. But yes, a singularity has no volume.
  8. Standard memberadam warlock
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    18 Aug '09 22:50
    Originally posted by divegeester
    Often illustrated as a dark swirling disc with little depth compared to width; what 3 dimensional shape is a black hole?

    Does it have dimensons? Should it be spherical? Is it mearly gravity creating an optical illusion of shape?
    I think that it was Roger Penrose who proved that under gravitational collapse a black hole always achive a spherical form.
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    19 Aug '09 03:43
    Originally posted by adam warlock
    I think that it was Roger Penrose who proved that under gravitational collapse a black hole always achive a spherical form.
    Under certain assumptions, yes.
  10. weedhopper
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    19 Aug '09 05:39
    One of the many programs circulating on the Science/Discovery channels about black holes was copyrighted 2009 and mentioned that some astronomer somewhere had detected a "bulge" in a black hole, making it less than spherical. Since a black hole can't be seen, I don't know how he came to his conclusion about the bulge, but then again, sometimes I watch these shows just for the background space music...
  11. Cape Town
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    19 Aug '09 08:15
    Originally posted by KazetNagorra
    But yes, a singularity has no volume.
    I am not sure if there is actually any evidence that zero volume singularities actually exist. However, for the purpose of this discussion I will assume we are talking about the event horizon not the singularity.

    Also black holes are not necessarily spherical - and are almost certainly never perfectly spherical. They probably all have some amount of bulge along their equators (as do most rotating bodies), and some variation too.

    I suspect that it is even possible for binary stars to collapse into a single black hole yet still rotate around each other within the hole creating a rotating oblong shape.

    I read in scientific american that 'naked black holes' could occur. I believe this means singularities without an event horizon, but I didn't really understand it all.
  12. Subscriberdivegeester
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    19 Aug '09 10:18
    I'm no expert either by any means!

    The swirl effect we see in the disk is created by magnetic fields within the black hole - inside the event horizon? So if only magnetic fields can escape from a black hole, can we presume that the only distortion we see is from matter outside of the black hole just prior to the event horizon? But, isn't the event horizon a spherical event? It must be surely - so we have a spherical event which causes matter to rotate around it in a flat disk?

    Back to sky sports I think!!
  13. Standard memberPalynka
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    19 Aug '09 10:23
    Originally posted by divegeester
    I'm no expert either by any means!

    The swirl effect we see in the disk is created by magnetic fields within the black hole - inside the event horizon? So if only magnetic fields can escape from a black hole, can we presume that the only distortion we see is from matter outside of the black hole just prior to the event horizon? But, isn't the event ...[text shortened]... vent which causes matter to rotate around it in a flat disk?

    Back to sky sports I think!!
    LOL! That is exactly how I feel about this.
  14. Standard memberadam warlock
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    19 Aug '09 11:49
    Originally posted by FabianFnas
    Under certain assumptions, yes.
    Under all assumptions. If it is a gravitational collpase than the form will always be spherical.
  15. Standard memberadam warlock
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    19 Aug '09 11:511 edit
    Originally posted by twhitehead
    Also black holes are not necessarily spherical - and are almost certainly never perfectly spherical.
    It has been proven for some time that under gravitational collapse a black hole is always spheric in shape.

    Just checked some notes. This happens in time for rotating black holes. It isn't immediate but it always happen after a period of time.
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