Black Holes Disputed

JScarpace writes: "Researchers at the Los Alamos National Laboratory in New Mexico and at the University of South Carolina in Columbia have proposed the existence of "gravastars" which are bubbles of superdense matter. If they are correct, the idea of a black hole with a singularity at the center may be just a fantasy."

Comments

Here's their paper

[pepik_knize]

4 pages in your choice of formats here.

Re:Here's their paper

[KjetilK]

Thanks a lot! Saved me the trouble of searching! :-) However, it should be emphasized that this is a pre-print, it could have changed substantially when going through peer-review.

Also, folks, don't slashdot the site unless you know a bit about cosmology (if you don't know what I'm talking about when I say "line element" forget it) - this is a site that is very important for physicists in their daily work.

Re:no singularity...

[ndevice]

there's also the people who think that the singularity never forms in the observable lifetime of the black hole because as the center mass contracts, things slow down (because time / speed of light is 'apparently' slower in gravitational fields)

Your own reference seems to contradict you

[BlueUnderwear]

Go to the smoke experiment, and scroll down to the bottom of the page, to see what happens when the angle of attack becomes too big. Yes, the upper and the lower flow no longer meet. Hence the reasoning that the top flow must be faster simply because it has a longer way to do is not really correct. Conceivably it could come out behind the bottom stream, or, as observed, ahead.

Hey, it even says so, in bold: Stating that the fluid flowing above the airfoil is accelerated with respect to the fluid flowing below it ``because it must travel for a longer route in the same time'' is then definitely wrong. Betrayed but your own reference texts, eh?

As harlows_monkey says, in order to understand why the streams do meet if there is a correct angle of attack, you do need deeper insight into aerodynamics than is spelled out in the simple "lay-man's" explanation.

How to form such a beast?

[Captn Pepe]

According to the article (in gr-qc/0109035, not the horrible thing linked from the /. article above), we essentially have a phase transition that results in an inflationary subspace inside this thin shell! I grant that, for some odd assumptions, this might be a stable solution, but I kind of doubt it. It has been proposed before that the collapse to a singularity triggers internal inflation, which is plausible but still gives a black hole, not a "gravstar".

Anyway, and I quote from their own article, "Here we forgo any discussion of the details of the quantum phase transition and present only the solution of Einstein's eqs." Mazur and Mottola have no clue how to make such a beast, either. If nothing else, the energy density wouldn't approach that needed for a phase transition until long after the entire assemblage was well within its own event horizon, again giving -- you guessed it! -- a Schwartzchild black hole. Recall, when a solid mass reaches the density required to fall within its own event horizon, the total density isn't much above nuclear densitites. During big bang baryosynthesis, densities are easily this large and inflation obviously didn't occur then (or else we'd have no protons in the universe).