NetNews Usenet Archive 1992 #26/NN_1992_26.iso/spool/sci/physics/18341

Text File | 1992-11-08 | 1.6 KB | 36 lines

Newsgroups: sci.physics
Path: sparky!uunet!snorkelwacker.mit.edu!tamsun.tamu.edu!zeus.tamu.edu!dwr2560
From: [e-mail] (RING, DAVID WAYNE)
Subject: Re: Question on Hawking radiation
Message-ID: <[e-mail]>
Summary: Why don't extremal black holes radiate?
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Date: Sat, 7 Nov 1992 01:05:00 GMT
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[e-mail] (David E. Brahm) writes...
>Can anyone explain why extreme Reissner-Nordstrom black holes (Q=M) [or
>charged Kerr solutions, L^2 + Q^2 = M^2] have a vanishing Hawking
>temperature (T=0)?  The virtual-particle picture would make me erroneously
>believe that positively-charged particles would spew out from the vicinity
>of a positively-charged black hole.  My guess is that it has something to
>do with the inner horizon (r-) going to zero.
>[* This question is originally due to Dr. Stephen Hsu at Harvard *]

A stationary observer just outside the horizon does not accelerate (as measured
from outside, i.e. if she is lowered from infinity on a string the string has
no tension). Thus, what looks like a particle pair from outside, looks like a
particle pair in a local inertial frame. And pair production from nothing is
forbidden in inertial frames.

But this suggests another harder question: how can the surface gravity be
zero???

BTW If you talk to Steve, say hi for me. :-)

Dave Ring
[e-mail]