Stable Blackhole?

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If a stable BH exists?. By stable I mean not growing and not shrinking.
How then does its radius depend on a homogenious (or inhomogenious?) density outside this BH? I suppose its radius is then anyhow larger than its Schwarzschild radius.
 

Nabeshin

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If a stable BH exists?. By stable I mean not growing and not shrinking.
.
I guess you could have a black hole in which mass loss by hawking radiation is exactly balanced by infalling matter. In principle however, you're either going to have to have a darn small black hole (because hawking radiation is pitifully small otherwise), or a black hole in a very very empty region of space (not usually where black holes form!).

Since the only source for black holes of significantly lower than stellar mass ranges is the very early universe, and no such primordial black holes have been observed, it is not likely that completely static BHs exist in nature.

Edit: Some numbers to give an idea of the latter situation in which a BH would be in equilibrium by being in an empty region of space:

A 1 solar mass black hole radiates about 9*10^-29 J/s, which translates to a mass loss of about 10^-45kg/s. An electron has a mass of roughly 10^-30kg, so that's the equivalent of the black hole encountering one electron every 10^15 seconds, ~31 million years. Well, that gives you a scale of just how damn empty things would have to be for the black hole to be at equilibrium.
 

marcus

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If a stable BH exists?. By stable I mean not growing and not shrinking...
I guess you could have a black hole in which mass loss by hawking radiation is exactly balanced by infalling matter...
This seems to open up an interesting line of questions. What alternatives are possible to the conventional Schwarzschild, Kerr etc pictures?

I personally don't have enough information to comment on the broader topic of nonstandard BHs, but maybe someone else can.

Did anyone see the SciAm article by Pankaj Joshi that appeared in January 2009?
http://www.sciam.com/article.cfm?id=naked-singularities

Do we already have a thread on non-standard collapse models? Should we start one? (If we don't have one already.) What should we call it? Any ideas?

I think it's timely because GRB that can accompany collapse are increasingly studied and classified using new instruments. Sudden gravitational collapse has become, so to speak, observational rather than just a theoretical subject.

We can, in effect, watch the formation of BHs. And they may possibly be different from what the earlier static models suggested.

Hurk4, if you are interested in the broader topic, maybe you could start a more inclusive thread?
 
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