The gravity gradient at the event horizon of a small, low-mass black hole
is much greater than the gradient at the event horizon of a large, very
massive black hole. The smaller the black hole, the stronger the tidal
force at the event horizon.

So pairs of virtual particles are often pulled apart by the gravitational
tide near the surface of a small black hole, but very rarely pulled apart
by the tide near the surface of a large black hole. Thus, small black
holes emit particles from just above the event horizon at a high rate,
while large black holes emit particles at an extremely low rate.

-- Jeff, in Minneapolis

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http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves