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Thread: What are black holes, and equation involved in it?

  1. #1 What are black holes, and equation involved in it? 
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    hi, newbie for physics here

    i just wanted to know about black holes and equation involved in them.
    What made light cannot escaped through it, if so, then how one could observe a black hole since no light coming from it?

    Please correct me if i'm wrong, tx.


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    Moderator Moderator Markus Hanke's Avatar
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    Nothing can escape from below a black hole's event horizon, because all possible trajectories of bodies will end in the singularity. You can still observer black hole's by the gravitational effect it has on its surroundings.


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    Quote Originally Posted by The Asian View Post
    What made light cannot escaped through it, if so, then how one could observe a black hole since no light coming from it?
    Think of yourself driving a car on a road that is properly banked. Banking a road means that the outer edge of a curve is elevated.
    http://physicslearning2.colorado.edu...nked_Curve.gif
    If the curve is properly banked, as your car enters the curve, you would keep the steering wheel straight. You would move in essentially a straight line- through a curve.
    http://www.webassign.net/serpop/5-13.gif

    Now, I admit the analogy is weak, but you get the idea.

    A black hole warps spacetime in its vicinity so heavily, that any 'road' light takes to exit is banked heavily enough to lead light back inside - in a straight line.
    Light has no mass, but it does propagate in space. If space is curved, then light will follow the curve in a straight line, causing 'lensing.'
    https://en.wikipedia.org/wiki/Gravitational_lens
    This effect near a black hole is so severe that all curves lead back inside.

    Quote Originally Posted by The Asian View Post
    i just wanted to know about black holes and equation involved in them.
    What equations specifically?
    You might start here:
    Schwarzschild radius - Wikipedia, the free encyclopedia
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    thanks for the information.

    the equation of its gravitational force, is it the same with newton's?
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    Quote Originally Posted by The Asian View Post
    the equation of its gravitational force, is it the same with newton's?
    Black holes are the result of some solutions of the Einstein Field Equations in general relativity; these solutions are not force laws as in classical Newtonian mechanics, but space-time metrics. For black holes you have the following main solutions :

    Schwarzschild metric - Wikipedia, the free encyclopedia ( uncharged, static black holes )
    Kerr metric - Wikipedia, the free encyclopedia ( uncharged black holes with angular momentum )
    Reissner ( charged, static black holes )
    Kerr ( black holes with both electric charge and angular momentum )

    It is in principle possible to write down force field equations for these, but unlike Newtonian mechanics these would be very complicated expressions, and not simple inverse square laws. So to answer you question - no, they are not the same as Newton's.
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    thank you that answer the question
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    Quote Originally Posted by The Asian View Post
    thank you that answer the question
    No problem
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