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Is a black hole black from all directions?

  1. Aug 19, 2014 #1
    Black holes are usually shown as funnels. Is there one "funnel" pointing in a single direction or are there event horizons and "funnels" seen from every direction?
     
  2. jcsd
  3. Aug 19, 2014 #2
    There are no such funnels; what they are showing you in that classic image is that a black hole curves spacetime quite drastically, to the point of "infinity" (not to be taken literally however.) It simply attempts to show you in three dimensions what actually happens in four.

    As for the question if they are black from all directions, the answer is, preliminarily, both yes and no. It depends on whether the black hole has angular momentum (and I *think* also charge) and if a singularity can, other than in theory, be effectively "naked" (ie. observable.) If you are thinking of the typical non-rotating black hole, then you'd see a black sphere - and of course a lot of gravitational lensing of the background around it.
     
  4. Aug 19, 2014 #3

    Chronos

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    A black hole, by definition, does not emit EM radiation. In that sense it is invisible in all directions. There are, of course, caveats. It is still indirectly detectable via gravitational lensing of background radiation and by emissions from any accretion disk it may possess. Typically, accretion disk emissions are most easily detected at high frequency wavelengths.
     
  5. Aug 20, 2014 #4
    So a black hole is an isotopic gravity source? Space-time is uniformly warped in all directions?
     
  6. Aug 20, 2014 #5
    A Schwartzchild black hole? Yes. As for the others, I would not risk an answer. You should really investigate the whole subject of rotating black holes and naked singularities, that's where your answer is at. Anyway, just keep in mind the funnel image is just a representation; a black hole does not behave any differently than any other concentration of mass - they all warp spacetime. There is no sun-funnel, no Earth-funnel and no black hole funnel. If you'd always see a black hole/circle/sphere from any angle or a bizarre oval or anything else, it depends on whether it rotates or not at the very least.
     
  7. Aug 20, 2014 #6

    WannabeNewton

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    As a guywithdoubts said, this is only true of Schwarzschild black holes. A rotating black hole is not spherically symmetric and therefore neither is the rotating space-time it generates. The same goes for rotating stars. However it must be emphasized that black holes are not objects sitting in space like stars. A black hole is space-time geometry itself. You must keep this in mind so as to not confuse yourself conceptually.

    I couldn't resist quoting this beautiful statement from Chandrasekhar: The black holes of nature are the most perfect macroscopic objects there are in the universe: the only elements in their construction are our concepts of space and time.
     
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