From: nuny@bid.nes   
      
   On Sunday, February 5, 2017 at 12:03:40 PM UTC-8, knha...@gmail.com wrote:   
   > hi hi   
   >    
   > I've been struggling with trying to model the following hypothetical   
   scenario,   
   > but it seems that it is beyond my abilities to figure out.  I'm hoping that   
   > someone here might be able to provide an answer or at least point me in the   
   > right direction.   
      
     Okay, here we go...   
      
   > The scenario:   
   >    
   > An object is falling into a black hole.  As the object passes the event   
   > horizon, another black hole approaches at relativistic speeds.  For a moment,   
   > the object is at L1 between the two black holes, and then the two   
   > singularities start moving apart again into a highly elliptical orbit.   
      
     Can't happen. Either the two BHs were already co-orbiting or they're doing a   
   one-time mutual hyperbolic (not quite actual hyperbolics because the focus of   
   each BHs orbit is also moving, but still) close pass. Capture requires one or   
   the other to lose    
   momentum to some other body which then goes into a higher orbit or is ejected.   
   If accretion disks are present they count as "bodies".   
      
     That aside, ignore what came before and what happens later, and look at it   
   from the BH-system center-of-mass. You have two BHs approaching each other   
   relativistically while the object is falling into one of them.   
      
   > So the question is: is there any hypothetical configuration where the object   
   > can thrust away from the singularity, given the changing curvature of space   
   > time as the two singularities pass by each other?   
      
     Sure, why not? It all depends on the local geodesics available to the object   
   at any given time. The point, as you intuit, is that during the close pass the   
   geodesics are changing.   
      
   > Assuming the mass of the black hole is concentrated in the singularity (no   
   > fuzz balls or the like),   
      
     Doesn't matter. What matters is the geodesics available *where the object   
   is*.   
      
   > is it correct that: so long as the two singularities remain outside the event   
   > horizon of the other, there will exist world lines in which they break away   
   > from each other even if their respective event horizons intersect briefly?   
      
     No. If the event horizons merge at all, they stay merged. If the object was   
   between them when they merge it's Doomed.   
      
     If they don't, and if the object hasn't crossed the event horizon of the BH   
   it was falling into, the spacetime between the two BHs *might* flatten such   
   that the object can boost out to safety *if* it can exert enough thrust in the   
   right (changing as    
   the BHs recede from each other) direction.   
      
     If the object isn't quite exactly between them when they merge *and* if it's   
   moving properly (think spiraling rapidly in rather than falling straight in) I   
   *think* the object can use the locally flattening space between the merging   
   BHs to escape.   
      
     It depends on how close the object was, how close the BHs get at their   
   closest, and how much dv the object has available.   
      
     I'm not absolutely positive about that so don't publish it in a story and   
   credit me. ;>)   
      
      
     Mark L. Fergerson   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)