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starship-design: Blackhole, Railgun and superconductor

Timothy van der Linden writes:
 > >Actually, black holes produce _more_ energy the smaller they are.
 > >In fact, if you don't keep feeding it, it will explosively evaporate
 > >away.  Playing around with small black holes makes letting Calvin
 > >play with a flame thrower indoors look positively safe.
 > Are you sure about black holes producing more energy the smaller they are?
 > I've heard that they evaporate faster and faster, but that's only because
 > the surface:volume ratio gets bigger. I'd guess the total evaporated energy
 > gets less if the surface gets less.
 > But indeed if you would have 1000 small holes instead of 1 big with the same
 > total mass, you'd probably be better of with the 1000 small holes.

I believe Isaac is right about this.  Very small black holes evaporate
rapidly, to the point of being violently explosive.  The evaporation
rate is a function of the gravity gradient at the event horizon, which
goes asymptotic as the mass of the hole approaches zero.  Imagine the
energy release from a few hundred tons of mass turning into a spray of
high-energy subatomic particles within a tiny fraction of a second.