From: gdpusch@NO.xnet.SPAM.com   
      
   Sander Vesik  writes:   
      
   > Morenga  wrote:   
   >   
   >> Do black holes have Roche limits?   
   >> What if two black holes of equal mass approach each other?   
   >> Could they rip each other appart?   
      
   No, they will merge together to form a single big hole whose event-horizon   
   area is at _least_ as large as the combined event horizons of the two holes,   
   in accordance with the 2nd Law of Black-Hole Dyndamics. (The Three Laws   
   of Black-Hole Dyndamics are in exact analogy to the Laws of Thermodynamics,   
   with mass playing the role of "heat," the event-horizon area playing the   
   role of "entropy," and the gravitational acceleration at the event horizon   
   playing the role of "temperature.")   
      
      
   >> And how so as nothing is supposedly allowed to leave the "event horizon"   
   >> once it enters.   
      
   Simple --- they CAN'T !!!   
      
      
   > Black hole collisions have been extensively simulated due to the   
   > relativistic effects involved. As for nothing leaving the event horizon,   
   > see 'Hawking radiation'.   
      
   It is highly debatable whether Hawking radiation actually "leaves" the   
   event horizon. (Note that in Hawking's model, it "leaves" the horizon by   
   "traveling backwards in time," a concept more than a little problematic!)   
   A model that is physically more accurate is that gravitationally-induced   
   particle/antiparticle pair production occurs _OUTSIDE_ the event horizon,   
   and the member of the pair that falls into the black hole carries "negative   
   energy." ("Negative energy" is _also_ problematic, but rather less so than   
   "traveling backwards in time"...)   
      
      
   >> How does the grav field look like if two fluid bodies (like gas giants)   
   >> would approach each other? I mean they would not tear each other   
   >> appart but rather "flow" towards each other, right?   
   >   
   > Gas giants aren't entirely (or really mostly) made out of fluids. The   
   > pressure is too high so most of it is really solid.   
      
   Sorry, no. The pressure may be high, but so is the temperature !!!   
   Very few substances are "solid" under gas-giant interior conditions ---   
   not even the "metallic" hydrogen in their "mantles." One does not   
   generally get crystal formation unless the cores approach a degenerate   
   state --- and even then it is not a "normal" crystal, but a "coulomb   
   crystal" of pressure-ionized nuclei in a sea of degenerate electrons,   
   much like the crust of a white dwarf star.   
      
   As for the often-misused descriptive terms "rocky" for the core and   
   "icey" for the mantle, they refer to their _stochiometric compositions_,   
   =NOT= their physical states !!!   
      
      
   -- Gordon D. Pusch   
      
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