In a message dated 1/20/02 7:55:19 PM Eastern Standard Time, jlu@HEP.ANL.GOV
writes:
<< But the paper does not claim the non-existence of Black holes.
What it does do is claim another solution to the Einstein
equations that can simulate some of the effects of a black hole. What
the authors seem to be doing is making a model where a collapsing star
collapses into a spherical shell rather than simply shriveling into a
volume that eventually recedes inside an event horizon. The spherical
shell is located at the radius that would correspond to the event horizon
for the star's mass. Their claim seems to be that this mode of collapse
evades the Chandrasekhar limit. >>
Jack as I read this paper in the so called Gravastar model there would be no
event horizon and no singularity. They are proposing that rather than
complete collapse of a massive dying star, a region of strong "anti gravity"
( for want of a better word). would cause all the collapsing matter to be
confined to a thin membrane where the Schwarzchild classical event horizon is
predicted to be by black hole theory. This opposing force inside the membrane
prevents further collapse and any possibility of a singularity. Most
importantly, there is no information paradox, as predicted by the Bekenstein
equation. This would, I believe, invalidate Hawking's theory of black hole
radiation and t'Hooft's holographic theory. In the paper the interior inside
the Gravastar would have a negative energy density (effectively the same as
positive cosmological constant in that region of space). generating the anti
gravity force preventing further collapse. The membrane would a have a
positive energy density and the exterior energy density would be zero. The
Bekenstein equation for entropy is:
S_BH=4*Pi*K_b*M^2/hbar*C ( which equals
(Pi/2)*(K*C^3/Gh)*A_eh ) while in the gravastar model S= K_b*L*M*C/hbar
where L is the membrane thickness. Considering how much is invested in the
idea of the Berkenstein Bound, in membrane theory (Superstring theory) and
loop Quantum gravity for example, this paper is suggesting a serious change
of direction in physical theory. BTW personally I am very skeptical about
this proposal but I think it deserves serious consideration. As pointed out
by another Physicist on a different physics list measurements of stellar
black holes, like Cygnus X-1,demonstrated that there was no signature of a
"splash" of accreted matter impacting a hard surface. This result is
predicted to occur if this idea is valid.