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Thread: What if a black hole were to start spinning?

  1. #1 What if a black hole were to start spinning? 
    Time Lord
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    Would spinning really fast (still slower than the speed of light, of course) allow the concentrated, super-dense matter in a black hole to begin to defeat its own gravity?

    Remember, the density of it's matter doesn't just give it super tremendous gravity. It also gives it a super tremendous moment of inertia.

    I'm just curious where such a discussion would lead. Maybe a dead end, but it's still fun to contemplate.


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    WYSIWYG Moderator marnixR's Avatar
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    how fast is fast ? neutron stars spin pretty fast, but they don't fall apart as a result


    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  4. #3  
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    A black hole typically is spinning very fast because the angular momentum of the rotating star it originated from is concentrated into a small diameter, like an ice skater pulling their arms in closer to their body and spinning faster and faster. at least so the theory says.

    The moment of inertia does go up with increasing mass but it goes down with decreasing diameter. I don't know of any reason why the spin would cause the black hole to fly apart.
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    BH, do spin and at spins per second in some cases. the last time i posted whats written i really got slammed, so I'll suggest you Google *Black Hole Spin* and you will find many of NASA's illustration and estimates of spins per second.

    i question energy being effected by gravity to begin with, since its said light or energy has no mass to be effected. it is suggested that when matter is pulled into a BH (stars or debris) the process disintegrates matter, which means energy itself in what should be those parts, well below detection. one simulation from NASA, showing such a action plainly shows the light being sucked out of the star or that the energy levels fall below.
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  6. #5  
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    Quote Originally Posted by Harold14370
    A black hole typically is spinning very fast because the angular momentum of the rotating star it originated from is concentrated into a small diameter, like an ice skater pulling their arms in closer to their body and spinning faster and faster. at least so the theory says.

    The moment of inertia does go up with increasing mass but it goes down with decreasing diameter. I don't know of any reason why the spin would cause the black hole to fly apart.
    And I guess there's a maximum speed it can go up to. I wonder what ordinary matter does as it begins to approach it's maximum allowed relativistic speed. And then, with all that gravity, I wonder if it's even able to move in a wave at all.

    I can see why some people are so interested in them. A black hole's gravity changes so much about how we can imagine things, and at the same time, some of the changes seem like they'd be straightforward.
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  7. #6  
    Forum Ph.D. william's Avatar
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    Quote Originally Posted by Harold14370
    A black hole typically is spinning very fast because the angular momentum of the rotating star it originated from is concentrated into a small diameter....
    Bingo!
    Actually, I'd bet that all black holes are spinning.

    Cheers
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
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    As far as I'm aware black holes don't exist and therefore don't spin.
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    Forum Ph.D. Nevyn's Avatar
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    a very closed minded statement PsychoJames, would you change your mind if i showed you this?
    Come see some of my art work at http://nevyn-pendragon.deviantart.com/
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  10. #9  
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    Well I see the pic is dated 1995 and it says "Almost certainly this object is a black hole" that means it's someone's opinion. I have done some googling and found this article http://sciencenow.sciencemag.org/cgi...ull/2007/621/1
    It quite vague but it's something and resent. Tell me what you think.

    I have an open mind I just said I hadn't seen any evidence.
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  11. #10  
    Forum Ph.D. Nevyn's Avatar
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    Time has little to do with it: Pythagoras has been holdign up for over 2000 years now.

    This is just the same as black hoes (if not worse). "All of our calculations suggest this is quite plausible," there is no definate in 'quite', no certainty. The only difference between this and a black hole argument is that a black hole argument we have evidence (if limited). The article contains no scientific data, calculations or even supported conclusions.
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  12. #11  
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    To your initial question, my answer is "yes".......it would defeat it's own gravity.........it would become a star/sun.

    The sun actually has such a whirpool effect on space-time, that all the planets are basically warped in motion around it. If it didn't spin, presumably on it's inner surfaces, and not the fireworks display of sparks we see on it's outer-surface (that betrays the fact it has a substantial spin), it would collapse presumably into a black hole.

    It's a theory, it can't be proven, obviously, but........yeah.
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  13. #12 Re: What if a black hole were to start spinning? 
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    Quote Originally Posted by kojax
    Would spinning really fast (still slower than the speed of light, of course) allow the concentrated, super-dense matter in a black hole to begin to defeat its own gravity?

    Remember, the density of it's matter doesn't just give it super tremendous gravity. It also gives it a super tremendous moment of inertia.

    I'm just curious where such a discussion would lead. Maybe a dead end, but it's still fun to contemplate.
    Spinning black holes are actually quite interesting, they are called Kerr black holes if you are in the mood to google some info. Try skip the kerr-newman stuff as that adds an extra layer of complexity to the problem.

    For starters they have two event horizons, which opens up the issue of naked singularities if they spin fast enough; which might relate to your original question.

    As william stated, almost all "recent" black holes should be rotating to preserve their angular momentum.
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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  14. #13  
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    As objects are accelerated toward C they begin to increase in mass, right? Would a particle that was accelerated to that limit and beyond, which just barely missed the center of a black hole have any chance of being dense/massive enough to defeat its gravity and enter a near orbit?

    Or maybe a better question is: can a black hole orbit around another black hole? If so, can they orbit inside one another's event horizons?
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    Ya, one black hole could orbit another, I'm pretty sure there are black holes in the milky way that are orbitting the supermassive black hole at the center of the galaxy. As to orbitting within the event horizon, I could be wrong, but I don't think anyone can answer that. We don't truly understand what happens inside the event horizon, so who knows what another black hole would do. Maybe they would combine to create one larger black hole?
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