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Two Black Holes. No singularity.

  1. Mar 24, 2003 #1
    I watched a special recently in which there were two black holes observed and there was a single star between them. Instead of doing what a single black hole would do- pull the star into/onto it with it's imense gravity- the star stayed relatively the way it was because the black holes were simply canceling out eachother. Well If they could do this with a star then they would be likely to be the same for a person. If a spaceship (far in the future obviously...) was to go between the two black holes it would likely survive too. Also, if they cancel eachother out visibly (with the star) then isn't it likely that they cancel eachother out not visibly? As in they would NOT affect space time except in their immediate area (itself)? Unlike other black holes which would effect everywhere.
  2. jcsd
  3. Mar 24, 2003 #2
    A good idea at first glance, but ultimatly no. The black holes are themselves individual systems and do indeed warp spacetime as they should. It is merely the gravity/tidal forces that balance out. Two fairly equal magnitude forces in oppoisite directions will do this. Essentially the star is in a liberation point in the two black hole system. There should be 4 more positions as well.
  4. Mar 25, 2003 #3
    Two equivalent black holes approaching each other distort their intervening spacetime by mutual attraction so that between them their event horizons actually diminish!
  5. Mar 25, 2003 #4
    No, that is not correct. A black hole's event horizon must always increase, with the sole exception being when it consumes a single virtual particle in a virtual particle pair. The two black holes in this system would have their normal event horizons.
  6. Mar 25, 2003 #5
    Well I agree with Lauren mainly because I thought pretty hard about this and I got abbout the same thing... but you could be right brad can you give us mroe?

    In the other PF there was a topic about black holes and it was discussed that there is a chance a person could survive a black hole because they might be too small to be affected. I did not participate in the thread because at the time I knew less about black holes than I do now. I did, however, read some of that thread and that is what was discussed. If a person could possibly survive one, They could certainly survive between two that are canceling eachother out...
  7. Mar 25, 2003 #6
    Let us look at the system of what is occuring.

    We have two black holes orbiting each other. Each black hole is its own seperate entity. Yes they are bound by each other's gravitational pull since they are in orbit. We also know a black hole is a severe local curvature of spacetime, and far out it is like any other effect. This is why if the sun suddenly just turned into a black hole, most all the planets (save perhaps mercury) would remain in their current orbits. The two black holes orbiting each other would have no way to reduce each other's gravity. In fact they don't. What happens is a state of equillibrium akin to being in the center of the earth. Gravity is pulling on you equally from two opposite directions. The vectors sum out to zero, but they do exist. If you move out towards one you'll be pulled into it. Passing between two black holes is not the same as passing through one.

    If any other effects, the black holes may be a bit elongated due to tidal forces, but that is all. Eventually they will spiral into each other and the resulting event horizon will be much larger (the sum of the previous two).
  8. Mar 25, 2003 #7
    The vector reduction in gravity is local, in between the black holes. The overall surface area of the holes does not decrease.

    As the black holes approach each other, the original (distance-->infinity) facing event horizon volume (but not necessarily its area) diminishes as the escape velocity there falls below the speed of light. The holes' far horizons increase surface area more than enough to compensate for the interior area losses.
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