From: g_d_pusch_remove_underscores@xnet.com   
      
   bill_jones92057@yahoo.com (Bill Jones) writes:   
      
   > Generally, when the BH stops 'feeding', substantial portion of its   
   > galaxy will remain.   
      
   Indeed. The masses of all the central supermassive black holes we have   
   inferred to exist all seem to be around mere 0.2% of the host galaxy's mass.   
   Explaining why supermassive black hole masses are proprotional to the host   
   galaxy's mass and why the constant of proprotionality is so small is one of   
   the top 10 question about galaxy formation currently being studied by   
   astrophysicists.   
      
      
   > Is it possible that BH's exist which have 'eaten' their entire   
   > galaxies?   
      
   Highly unlikely. Black holes are not some sort of "Cosmic Vac-U-Suck(tm);"   
   they can only "eat" something that is _already_ on a collision course for   
   their event horizons. Once they have "eaten" all such objects, they stop   
   growing, until a rare chance gravitational interactions happen to perturb   
   a star onto an orbit that will collide with the black hole.   
      
   Furthermore, on a cosmic scale, even the largest supermassive black hole   
   ever inferred still has a diameter that is quite small compared with the   
   mean distances between stars --- even in the relatively "crowded" stellar   
   environment of a galactic core.  Since even the central supermassive   
   black hole represents a miniscule taget for even a star to hit, unless   
   a gravitational perturbation essentially "drops" the start almost perfectly   
   straight inward to within a microscopic fraction of a percent, the star   
   with miss the central black hole and simply continue on its new orbit   
   until it interacts with something else. Since the probability of even   
   _one_ star getting thrown into an orbit that hits the black hole is very,   
   very small, the probability that _ALL_ of them could get thrown into such   
   almost perfectly radial orbits is utterly negligible.   
      
      
   > If so, what might be the properties of such BH's?   
      
   They would have very large masses and diameters --- for a black hole.   
   However, their diameters would still be utterly negligible compared   
   to a galaxy, and they would not exert any more gravitational force   
   than the original galaxy that they "ate" did.   
      
      
   -- Gordon D. Pusch   
      
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