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Last straw to form black hole

  1. Aug 18, 2004 #1
    I'm in a rocket ship hovering at a non-black-hole Schwarzschild radius. The bottom half of my ship is inside the radius. I drop a straw. As the straw crosses the Schwarzschild radius, at mid-ship, it adds just enough mass within the radius to form a black hole. What would I see? Would the bottom half of my ship suddenly black out?
  2. jcsd
  3. Aug 19, 2004 #2


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    If the Schwarzschild radius of the mass is inside the bounds of mass itself (i.e. it's not compact enough to be a black hole), you'd have to be doing something pretty magical to be hovering above it -- you'd be in it.

    - Warren
  4. Aug 19, 2004 #3
    I don't understand your response. The bottom half of my spaceship is part of the interior mass. The top half, with me and the feather, is part of the exterior mass. I drop the feather and it falls to the bottom half which is inside the radius. That additional interior mass is just enough to make the black hole form. So what happens next?
    - Ray
  5. Aug 19, 2004 #4


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    The first sentence of your post is a contradiction due to you using the wrong definition of a black hole: if it has a Schwarzschild radius, then it already is a black hole. More on this in your other thread...
  6. Aug 20, 2004 #5


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    Too convenient. You would never see the 'straw' hit the event horizon. A time dilation thing.
  7. Aug 20, 2004 #6
    Okay, you say the straw would "freeze" above the event horizon. But what about the bottom half of my spaceship? Would I have a breached hull? Would I be torn apart by tidal forces? All this because I dropped a straw? What about an observer on the other side of the radius? When I dropped the straw would his side of the sphere instantly become an event horizon (allowing me to use the straw in the hole to send a faster-than-light message) or would the event horizon formation spread from my side to his side at the speed of light? If he withdrew matter from the far side before the event horizon wrapped around it, would the event horizon then unwrap back around to me, telling me that it's not really a black hole after all? (These difficulties would not occur if the event horizon at a spatial radius of zero.)
  8. Aug 20, 2004 #7


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    If the feather were to fall on something and add just enough mass to that thing so that it collapses and forms a BH, then the EH of that BH would beb less than the original radious of the mass before the feather landed, wouldn't it?

    So you couldn't have the feather fall onto the mass and make it collapse unless the original mass was inside your ship. If that were the case, then the mass that was occupying some amount of space inside your ship would now be replaced by a BH occupying less space inside your ship.
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