In a message dated 1/20/02 10:19:08 PM Eastern Standard Time, jlu@HEP.ANL.GOV
writes:
<< Where do the field lines of the the repulsive field originate and
terminate? The answer seems to be: on dark matter. Dark matter, in this
context, is a euphemism for Einstein's cosmological constant, which is not
related to the matter distribution. So where do the outgoing antigravity
field lines terminate? They had better terminate inside the shell;
otherwise the shell will no longer simulate a black hole.
What all this amounts to, I think, is that the authors are dealing
with a model that no longer presents a solution of the Einstein field
equations. And, in any event, there is always the possibility of an
algebraic error in their work. >>
Apparently this anti gravity region inside the membrane is balanced by the
inward force of the matter in the membrane. The boundary I would presume is a
balance point with zero net field lines. The authors claim, I believe, that
their model is a solution to Einstein's equations. However I wouldn't defend
their position based on my understanding. From a conceptional point, their
model has significant differences from the more standard model of a black
hole. However perhaps a better question would be what will we observe that is
different. One concrete prediction they make is a very large explosion, much
greater in energy content than a supernova, as these Gravastars are formed, a
Hyper Nova. In fact such explosions have been observed but cosmologist have
proposed other explanations for them. I am not sure if this proposal is a
better match to the data associated with those events. They also predict that
the spectra of the energy of these explosions would have unique signature
related to their model.
Finally the outer membrane would be very cold, far below the temperature
predicted by the Hawking model for the event horizon of a back hole. However
it seems to me that this would only be observable for low mass black
holes/Gravastars as even the Hawking temperature is very cold for large mass
black holes. How this could be measured with current technology I couldn't
say. I doubt that it can.
Other questions come to mind. What about are rotating Gravastars? Or
charged Gravastars? For black holes these conditions are described by the
Kerr Newman relationship. How do these properties effect Gravastars? Do these
factors modify the radiuses of the gravastar as they do the event horizons of
black holes? Seems like they should.
My own opinion, which in no way should carry much weight, is that the
smart money is on the reality of black holes. However this idea is, I
believe, worthy of serious consideration and exploration. If this theory is
validated by observation this would be a major paradigm shift for our ideas
concerning the fate of dying massive stars and cosmological theory.