exploding black holes

Discussion in 'Astronomy, Exobiology, & Cosmology' started by DRZion, Aug 25, 2009.

  1. DRZion Theoretical Experimentalist Valued Senior Member

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    Is it possible for a black hole to get torn apart?

    Assuming you have a small black hole, and you place it between multiple other black holes so that a uniform force is exerted on the event horizon of the black hole, could the black hole possibly get torn apart?

    Surely, black holes are affected by gravity.
     
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  3. BenTheMan Dr. of Physics, Prof. of Love Valued Senior Member

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    Strictly speaking, no.

    Probably you'd just end up having the small black hole fall into one of the bigger ones, or you'd set up some sort of bound state.

    Of course, black holes can evaporate, a la Hawking. In this case, a very tiny black hole decays very quickly.
     
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  5. DRZion Theoretical Experimentalist Valued Senior Member

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    But we can agree that black holes are still subject to gravitation, right?
     
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  7. Dinosaur Rational Skeptic Valued Senior Member

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    If Mars & Venus somehow became black holes, their orbits would be the same as they are now. The following is quite correct.
    Furthermore, the above phenomena would have no effect on Earth's orbit.
     
  8. Pandaemoni Valued Senior Member

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    Yes, but "torn apart" usually happens not because of gravity but because of differential stress placed on one part of any object versus another. If I take a rag doll and tear its arm off, that is how I do it.

    The problem is that a black hole has all of its mass compressed into a single point in space. There is no way to apply differential stress to an object with zero volume. The event horizon has a describable radius and shape, but the event horizon is really defined by the way light happens to behave in proximity to that zero-size singularity.

    That said, the event horizon can be warped away from being just a "sphere" depending on the local geometry of spacetime. So a event horizon of a black hole that was under the influence of other black holes might not appear (from my relative position) to be a sphere, it might look elongated, or cigar-shaped or, in the extreme, like a flattened shell pressed up against the event horizon of a larger black hole as it falls in. (Just as a spinning black hole's event horizon ceases to be spherical.)

    An interesting question is what sorts of topologies it could have. I have an intuition that it would remain simply connected no matter what stresses the event horizon was under, but intuition and math may not mix well here in the wee hours.
     
  9. Enmos Valued Senior Member

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    What about twin blackholes ? Could they, in theory, take bites out of each other, like double-stars do ? If they could even exist of course..
     
  10. prometheus viva voce! Registered Senior Member

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    No. If they are far enough apart to be two black holes they will simply orbit each other. If they get too close together they will coalesce to form one black hole whose mass is greater than or equal to the sum of the masses of the original two black holes.
     
  11. Pandaemoni Valued Senior Member

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    Again, the notion of as "bite" suggests that each black hole must have a size, but the singularities (which are the relevant part) are of zero size. They have no length, no width, and no height. The only "bite" that could be taken is to swallow the whole thing--which they could do.
     
  12. AlphaNumeric Fully ionized Registered Senior Member

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    Are you thinking of event horizon area, not mass? Two black holes spiraling into one another will throw out vast quantities of energy in the form of gravitational waves and then join to form one black hole whose event horizon area must follow the 2nd law of black hole mechanics.
     
  13. prometheus viva voce! Registered Senior Member

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    Yes. I was thinking horizon radius but it's area isn't it? My bad. Again.
     
  14. AlphaNumeric Fully ionized Registered Senior Member

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    Event horizon and radius are equivalent, since the event horizon of even a Kerr-Newman black hole is spherical but unfortunately its not synonymous with the mass unless the black holes are all Schwarzchild.

    Thinking about it I would imagine that you'd almost certain to end up with a K-N black hole if two black holes join because the new black hole would have to carry the angular momentum of the two infalling black holes, unless they were not orbiting but instead just collided head on. Sounds like an interesting problem (how difficult it is is another thing), to compute the angular momentum of the resultant black hole formed by two inward spiraling Schwarzchild black holes. If I didn't have so much work I'd be tempted to have a go.....

    /edit

    Actually gravitational radiation would almost certainly make the problem trouser dampeningly unpleasant.
     
  15. DRZion Theoretical Experimentalist Valued Senior Member

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    How exactly do gravitational waves transfer energy? I thought that gravity makes a potential well, meaning that objects in it have extra potential energy.

    In a hypothetical universe with only one black hole and nothing else, what would be affected by gravitational waves? Where would the energy be going?

    A-ha! I understand. Because a black hole is a singularity, it's mass being concentrated all in one point, there is no way for gravitational forces to exert different pressures on different parts of the singularity, since it has no surface area. Because it has no surface area, all gravitation acts equally on a point without the possibility of tearing.

    Is it implied in general relativity that light will only get trapped in a singularity?
    Or could a non-zero volume object exert enough gravitation as to trap light?
    Shouldn't the volume of the event-horizon remain constant even as shape is distorted?
     
    Last edited: Aug 25, 2009
  16. kaneda Actual Cynic Registered Senior Member

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    I considered this idea some time back. A black hole is down to mass which causes sufficient gravitational pull. If you had sufficient technology and could use two larger black holes and move them close enough on opposite sides so that the event horizons just started to merge, it could be that the material in the central one would literally flow into the other two and it would literally vanish. It is possible that when just a little bit is left in the middle that it would be below black hole mass and so explode very violently.
     
  17. DRZion Theoretical Experimentalist Valued Senior Member

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    This seems to refute your statement in that a black hole has to be zero-size. Supposedly after this radius is smaller than neutron degeneracy, meaning that there is no known force that would keep matter from collapsing further into a singularity.
     
    Last edited: Aug 25, 2009
  18. Nasor Valued Senior Member

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    It seems intuitively like you could hypothetically have an object that had a volume but whose gravity was so strong that light couldn't escape - assuming some sufficiently strong force was present to keep the matter from collapsing under its own enormous gravitation.

    Question for everyone who actually knows about this stuff: is it really accurate to say that the singularity has zero size? Even if the volume of the matter in the singularity is constantly shrinking, wouldn't it take an infinitely long time for it to actually achieve zero size?
     
  19. DRZion Theoretical Experimentalist Valued Senior Member

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    This video, at 4:10 mentions exploding black holes.
     
    Last edited: Aug 25, 2009
  20. Pandaemoni Valued Senior Member

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    That is true...I am basing my statements on what we know about black holes, and it is possible that there are forces we do not know about. Such is science. It's possible that the next time I microwave popcorn, a rare and heretofore unknown force causes the popcorn to convert to strangelets that destroy the Earth.

    Such is science...

    I do agree that the remnants of a black hole can evaporate under Hawking radiation and that in the last throes of that it has been suggested that black holes could explode but:

    (1) It's not another gravitation field that causes that, it's antimatter swirling into the blackhole and eliminating its mass making it smaller and smaller over eons.

    (2) It is eons. Black holes won't start actually "shrinking" until the Black Hole Era, 10^40 years from now. That is about 760,000,000,000,000,000,000,000,000,000 times the current estimated age of the universe. Until then, the cosmic background radiation and stray hydrogen atoms in space will still be strong enough to swamp out the effects of evaporation. At that point, every glowing star will have burned out.
     
  21. fedr808 1100101 Valued Senior Member

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    well technically speaking the quantum singularity in the black hole which is what causes it to suck in everything around it, is classified as something with infinite mass and absolutely no volume. technically speaking all black holes have the same power, but theya re different sizes depending on the size of the star theyre made from. Think about it, super colliders only collide a few atoms and since thats very little original matter, it makes a very small black hole, conversely, a blakc hole made from a large star is fairly large.

    they probably wont act on each other because theyre both relatively the same power.
     
  22. prometheus viva voce! Registered Senior Member

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    Corrections:

    The singularity in a black hole is a classical one, because general relativity is a classical theory. It indicates that our knowledge of gravity is incomplete an we need a theory of quantum gravity to fully understand it completely.


    Black holes don't suck anything. A black hole of the same mass as some star will have the same gravitational field for an observer away from the surface of the star (which is bigger than the horizon of the black hole.


    Black holes have finite mass. If we believe general relativity is the ultimate theory of gravity (which we don't) the singularity is a point of zero size and has infinite density, not mass.

    No, the gravitational field of a black hole depends on it's mass which as I've just stated is finite.

    :bugeye:

    The force that a black hole exerts depends on it's mass. If you have two black holes they will attract each other by their gravity. whether they have the same or similar masses makes no difference.

    Wow. That post was rubbish!
     
  23. fedr808 1100101 Valued Senior Member

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    anyways how often does this sort of thing happen?

    Im guessing maybe a binary star possibly, but given the fact that everything we know about a black hole is mostly speculation and the fact we cant see it, there can be many possible theory's
     

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