On 1 apr, 05:35, Erik Max Francis <m...@[EMAIL PROTECTED]
> wrote:
> Crown-Horned Snorkack wrote:
> > Suppose you have a Nordstr=F6m black hole.
>
> It's Reissner-Nordstr=F6m, by the way.
>
> > At large distance, both Newton gravitational attraction and Coulomb
> > repulsion increase with inverse square of distance. Therefore, you can
> > pick test bodies with suitable mass to charge ratio that the Coulomb
> > repulsion exactly compensates Newton attraction irrespective of
> > distance. The charge would not feel the presence of black hole.
>
> > What about close to black hole? Does a small test body with like
> > charge to Nordstr=F6m black hole still feel infinite attraction at
even
> > horizon and large but finite attraction outside and near the horizon?
>
> We've already covered these cases in past questions. With a normal,
> stable black hole of any type, the event horizon presents a boundary
> through which one can never escape. It depends on the properties (mass,
> angular momentum, charge) of the black hole, not of objects falling
> near/into it. Inside the event horizon, the radial coordinate turns
> timelike and to move forward in time is to move closer to the
> singularity and one's inevitable destruction. In general relativity,
> gravity isn't simply a force; it's part of the structure of spacetime.
> And inside such an event horizon,
>
> > What about a Nordstr=F6m black hole and test bodies such that the
> > Coulomb repulsion exceeds the Newton attraction for all large
> > distances? Does the infinite attraction at event horizon still apply?
> > And would there also be large but finite attraction outside and near
> > event horizon? As well as large but finite Coulomb repulsion somewhere
> > outside?
>
> The special cases are for extreme Reissner-Nordstr=F6m black holes, and
> beyond-extreme holes. The beyond-extreme holes have ****d singularities
> and aren't thought to be physical (especially since the enormous
> charge-to-mass ratio that would be required which would make them
> basically impossible). The extreme case is interesting but is also
> thought to be academic; there, the inner and outer event horizons meet
> together to make a single event horizon, but curiously, the radial
> coordinate does not become timelike inside it; it remains spacelike. So
> you can enter the event horizon and exit out of it again ... but you
> exit out of it in another universe.
>
> However, since extremal black holes require charge and mass ratios that
> are perfectly balanced (and enormous), they are unstable,
Towards what?
> and thus not
> thought to represent anything physically possible.
>
> > Can you throw charges at Nordstr=F6m black hole, which are repelled by
> > Coulomb repulsion but cross the barrier by their kinetic energy and
> > add to the charge of the hole?
>
> Sure, if you throw it hard enough to overcome Coulomb repulsion.
>
> > How far can that process go?
>
> I do not believe you can make a non-extremal Reissner-Nordstr=F6m into
an
> extreme one by adding charge, though I might be mixing that up with Kerr
> black holes and adding angular momentum. (I think they're all part of
> the same case with Kerr-Newman holes, though.)
>
But technically, you could asymptotically approach an extremal hole,
right?
The properties of 1 solar mass Schwarzschild black hole are well
known. Its Schwarz****ld radius is 1,48 km. And its gravitational
field, at larger distances, is indistinguishable from the field of an
extended object of the same mass.
What is the charge of an 1 solar mass extremal Nordstr=F6m black hole?
What would be the electiric field strength at 1 a. u.?
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