Re: A partial black hole?

George W Harris wrote:

> 	Just jumping in here as a convenient point: 
> what about ultralarge black holes?  Schwarzchild 
> radius goes up, IIRC, as the square root of the mass, 
> so the larger the black hole, the lower the density 
> required to create it.

Schwarzschild radius goes up in direct pro****tion to the mass, actually. 
  So density goes as the inverse square of the mass.

> One could have a region of 
> space with an overall density approximately that of a 
> globular cluster, say, that would qualify as a black 
> hole.  I guess the aggregate gravitational field would 
> still be sufficient to cause a collapse into a singularity?  
> Such a collapse could still take millenia...

A globular cluster like M80 has an average density of something like 10 
stars/pc^3 (though this can vary quite a bit depending on the cluster), 
which is about 7 x 10^-19 kg/m^3.  A black hole corresponding to that 
density would have a mass of 1 x 10^49 kg, or about 5 x 10^18 solar 
m***** -- that's far greater than the mass of any known galaxy (which 
only get up to 10^12 solar m***** or so).

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