Re: Singularity destroys planet.

John Park wrote:
Erik Max Francis (max@xxxxxxxxxxx) writes:
Luke Campbell wrote:
On May 18, 9:09 pm, Erik Max Francis <m...@xxxxxxxxxxx> wrote:

The answer is much, much faster than it loses its mass through Hawking
radiation. It's an especially big problem here: We're talking about a
black hole that's smaller than a proton. The electromagnetic
interaction is gazillions of times more powerful than the gravitational
interaction. If it swallows something charged (which it invariably
will) then it vastly more likely to swallow something of opposite charge
to neutralize itself rather than swallow anything else. It'll pass
through, alternatively acquiring and neutralizing charge, but it's hard
to see how there'd be any net effect on that basis alone.
If the black hole does swallow a charged particle, it will suddenly be
able to lose energy by exciting electronic excitations in the matter
it passes through. When charged particles travel through matter, they
cause more excitations (and thus lose more energy) at lower speeds
than they do at high speeds. Compared to most charged particle
radiation, a gravitationally bound black hole will be traveling very
slowly, and will thus be leaving a significant ionization track and
losing energy significantly faster (per unit length, at least, if not
per unit time) than your typical proton or electron radiation. In
this sense, as soon as the BH becomes charged, it acts like a brake,
quickly slowing the hole down compared to the rate you would expect
from just swallowing particles.

This leads to additional braking forces when combined with Hawking
radiation - if the hole is hot enough to emit charged particles, it
will have a fluctuating electric charge as it sometimes spits out an
electron, sometimes a positron. In those times when it is charged, it
will experience additional drag due to ionization when it is going
through matter.
Sure. But, as I said, the flip side of that is that it will only stay charged for extremely short periods of time. The timescale of radiating away net charge is much faster than radiating away mass due to Hawking radiation. And, once it's already small enough to emit net Hawking radiation, it's going to preferentially emit similarly-charged particles for fairly obvious reasons (if you have a virtual particle-antiparticle pair and one is caught and one escapes and becomes real, then it's going to be much more likely to capture the oppositely-charged one).

It isn't just that a charged black hole will preferentially capture opposite charges, which it will -- it will radiate away its charge through Hawking-like processes at a much faster rate than simple Hawking radiation.

And in any case, what's the charge / mass ratio likely to be? We're
talking about a couple of electron charges helping to decelerate the mass
of an asteroid.

For black holes that small you'll probably get charges of +-e, maybe +-2 e, for split seconds. Divided by the whatever the mass of the hole is; for the kinds of black holes we're talking about, they're the masses of large asteroids or moons.

--
Erik Max Francis && max@xxxxxxxxxxx && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM, Y!M, Skype erikmaxfrancis
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-- The Russian, _Chess_
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Relevant Pages

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