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Could light orbit a massive object, like a black hole?

  1. Aug 18, 2015 #1

    H Smith 94

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    According to Hawking [1] it is posited that light photons at the event horizon of a black hole must cease to move, and remain motionless for the entire lifetime of the black hole.

    It is also observed [http://dls.physics.ucdavis.edu/~scranton/LensedCMB/a2218.gif] (and calculated) that the path of light will be bent by a sufficiently massive object, due to the curvature of spacetime around that object.

    Now, since gravity is a long-range force, I was wondering if it is possible for conditions to exists under which a photon could orbit an object due their gravitational attraction? If so: what would these conditions be; how can we observe it; and what implications, if any, does this have?
     
    Last edited by a moderator: May 7, 2017
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  3. Aug 18, 2015 #2

    Orodruin

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    Note that this is only true for light that would be moving radially outwards. All other light will inevitably enter the black hole and eventually reach the singularity.

    There is a circular light-like orbit at 3/2 times the Schwarzschild radius.
     
  4. Aug 18, 2015 #3

    A.T.

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    https://en.wikipedia.org/wiki/Photon_sphere
     
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