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frenchy
2002-Jan-16, 09:32 PM
I wasn't sure if I should put this in General Astronomy or here since it is an idea put forward by mainstream scientists but it is somewhat against the mainstream.

I just attended a talk by Emil Mottola of Los Alamos in which he presented a new static solution to Einstein's equation. In this case black holes are not singularities, there is no event horizon and no hawking radiation is emitted. He argues that such a solution reproduces all the observed (or observable) properties of black holes without the problems associated with their current classical and semi-classical models.

This isn't my field and so I'll just quote the abstract for his talk. Other people more familiar with GR will, I'm sure, answer any questions that may pop up on this. The talk was very nice btw.

The three regions described below are characterized by their equation of state. The inner de Sitter region has a pressure=-density EOS, the transition region has a Pressure=density EOS, and the outer Schwarzschild region has a zero Pressure and density vaccuum EOS.

"The solution is characterized by an interior de Sitter region of gravitational vacuum condensate with an exterior Schwarzschild geometry of arbitrary total mass M. These are separated by a thin shell with a microscopic but finite proper thickness of ultracold matter, replacing both the Schwarzschild and de Sitter classical horizons. The new solution has no singularities, no event horizons, and a globally defined timelike Killing field. Its entropy is maximized under small fluctuations and is given by the standard hydrodynamic entropy of the thin shell, which is of order M, instead of the Bekenstein-Hawking entropy formula (which is of order M^2). Hence unlike black holes, the new solution is thermodynamically stable and has no information paradox.

The formation of such a cold (1 mu K) gravitational condensate stellar remnant very likely would require a violent collapse process with an explosive output of energy. It is interesting to speculate that the formation and excitation of such objects may provide efficient central engines for very high energy sources in the universe."

DStahl
2002-Jan-17, 08:17 AM
I had not heard of this before. I be durned.

Here's a link to the request page for a paper on gravitational condensate stars by Mazur and Mottola; I wanted to post the link before I went ahead and delved into the document itself (so's I don't forget to share).

http://xxx.lanl.gov/abs/gr-qc/0109035

Don Stahl

[Later: Oooo! I cannot thank you enough for bringing this up. After scanning the paper quickly I see that I'm going to have to educamate myself on vacuum or gravitational condensates, which seem to be analogous to Bose-Einstein condensates. Thanks again!]

<font size=-1>[ This Message was edited by: DStahl on 2002-01-17 05:00 ]</font>

Chip
2002-Jan-19, 05:01 AM
Wow that's pretty wild. Thanks for posting this. I'll have to look into this further. If this were a closer model of the actual structure of a black hole, it's still a bizarre and downright spooky object, and here somewhat different from the event horizon -- infinite collapse model. Not to mention the term "globally defined timelike Killing field." Not sure exactly what that is before reading the paper -- but its creepy sounding too.

DStahl
2002-Jan-19, 04:34 PM
Here are some supplementary references for the paper on black hole physics:

On description of black holes using loop quantum gravity theory--apparantly a method of treating an event horizon as a manifold of 2-spheres. The physics of isolated horizons (http://www.phys.lsu.edu/mog/mog14/node7.html), Danial Sudarsky.

A Caltech page (http://nedwww.ipac.caltech.edu/level5/March01/Carroll3/Carroll5.html) on the GR and Killing's equation. Strong math.


I can't find anything enlightening on "gravitational condensate" or "vacuum condensate." Help!

Don Stahl

lpetrich
2002-Jan-20, 10:17 AM
This solution requires that the black hole's interior have a rather odd equation of state:

(pressure) = - (mass-energy density)*c^2

Yes, a big negative pressure. It can be produced by a scalar quantum field that is essentially constant in space and time. And other particles/fields have to be essentially absent.

There is no elementary particle known to exist that is described by such a scalar field; however, such particles are predicted by various unified field theories, like the electroweak theory. But such particles would be much more massive than most familiar ones, and it is not clear that nearly pure fields of such particles would be produced by gravitational collapse.

Also, a "globally defined timelike Killing field" is actually rather simple: it means that one can define a time coordinate everywhere so that the solution looks the same no matter how much one shifts that time coordinate.

Chip
2002-Jan-20, 07:56 PM
On 2002-01-20 05:17, lpetrich wrote:

"...Also, a "globally defined timelike Killing field" is actually rather simple: it means that one can define a time coordinate everywhere so that the solution looks the same no matter how much one shifts that time coordinate."



Hence the term "globally defined."

Also you mentioned, "other particles/fields have to be essentially absent." Would not this absence be disturbed by in falling radiation and matter -- or perhaps in falling matter remains outside. (I'm still reading this and haven't fully grasped things as you can see.)


<font size=-1>[ This Message was edited by: Chip on 2002-01-21 15:03 ]</font>

DStahl
2002-Jan-21, 09:30 AM
Here's an article (I believe it's credited to "New Scientist") on Mazur & Motolla's hypothesis. Very nice non-technical piece with some opinions pro and con. www.cosmiverse.com/space01170204.html (http://www.cosmiverse.com/space01170204.html). Brought to my attention by Elledan on physicsforum.com, and well worth a look.

Don Stahl

<font size=-1>[ This Message was edited by: DStahl on 2002-01-21 04:32 ]</font>

ToSeek
2002-Jan-21, 02:00 PM
Is this consistent with the (admittedly tentative) findings of an event horizon? (http://www.space.com/scienceastronomy/astronomy/death_spiral_010111.html)

DStahl
2002-Jan-21, 06:53 PM
Well, I really don't know. Here's a brief quote from the article mentioned above:

"According to Mazur and Mottola's calculations, [the vacuum condensate] would exert an outward pressure. Because of this, infalling matter inside the shell would do a U-turn and head back out to the shell, while matter outside the shell would still rain down on it."

Later on it's mentioned that matter falling onto the shell of the gravitational condensate star ("gravastar") would disintegrate in a "burst of pure gravitational energy." I truly don't know whether that mechanism could be expected to have the same emission signature as the observations described in the article you linked. It certainly seems like one test of the theory!

Kaptain K
2002-Jan-21, 08:43 PM
Question (may be showing my age)
When did Cygnus X-1 become Cygnus XR-1? /phpBB/images/smiles/icon_confused.gif

ToSeek
2002-Jan-22, 03:46 PM
On 2002-01-21 15:43, Kaptain K wrote:
Question (may be showing my age)
When did Cygnus X-1 become Cygnus XR-1?


With the new model year? /phpBB/images/smiles/icon_wink.gif

Wiley
2002-Jan-22, 11:37 PM
It's my belief that nature does not allow singularities. Our mathematical models of nature may have 'em, but in nature, they do not exist. A non-black hole example: the electrostatic potential from a point source is singular at the source. We know that vanishingly small point source does not physically exist. The electron, which is probably the closest to the ideal point source, does not exhibit this singularity. For this case, the singular mathematical model is not valid.

I believe that when we have a working theory of quantum gravity, we will find that the black holes are not truly singular. Very close, but not truly singular.

This does not mean I accept their hypothesis. As others in this thread have pointed out, there are still too many "if's". Regardless, it's an interesting idea.

<font size=-1>[ This Message was edited by: Wiley on 2002-01-22 18:38 ]</font>

DStahl
2002-Jan-23, 09:34 PM
I might argue that "singularity" in terms of GR really means "undefined" and not "a point of infinite density and zero spatial dimensions" even though that latter description seems to be the one a lot of writers imply. Kip Thorne, in his prologue to Black Holes and Time Warps, imagines someone trying to calculate the size and shape of a BH singularity:

"But then you remember that space can be so extremely warped near the singularity that the chaotic region might be millions of kilometers in radius though only a fraction of a centimeter in circumference..."

My personal guess would be that GR is telling us that there is a set of conditions under which the theory is not reliable, but it really can't tell predict anything concrete like absolute density or spacetime shape of the place where those conditions apply. (If that makes any sense...usually I'm full of beans, so add grains of salt to taste...*grin*)

Don Stahl

Wiley
2002-Jan-23, 10:04 PM
On 2002-01-23 16:34, DStahl wrote:
I might argue that "singularity" in terms of GR really means "undefined" and not "a point of infinite density and zero spatial dimensions" even though that latter description seems to be the one a lot of writers imply. Kip Thorne, in his prologue to Black Holes and Time Warps, imagines someone trying to calculate the size and shape of a BH singularity:

"But then you remember that space can be so extremely warped near the singularity that the chaotic region might be millions of kilometers in radius though only a fraction of a centimeter in circumference..."

My personal guess would be that GR is telling us that there is a set of conditions under which the theory is not reliable, but it really can't tell predict anything concrete like absolute density or spacetime shape of the place where those conditions apply. (If that makes any sense...usually I'm full of beans, so add grains of salt to taste...*grin*)

Don Stahl


I agree with you. The term "singularity" obviously comes from the mathematical definition of "singularity", which is non-analytic. So its not the function that is undefined but its derivative. (Both |x| and 1/|x| are singular at x = 0.)

My guess is the same as yours: when the equations become singular, it indicates you're bumping up against the limit of the theory.

ToSeek
2002-Apr-23, 02:18 PM
More on the subject:

Black holes aren't holes (http://www.sciencedaily.com/releases/2002/04/020423075643.htm)

We've already established that they aren't black. Should they get a new name? /phpBB/images/smiles/icon_wink.gif

SpacedOut
2002-Apr-23, 03:28 PM
John Kierein just posted a link to an interesting article on this subject “Gravastars” in this
General Astronomy thread (http://www.badastronomy.com/phpBB/viewtopic.php?topic=1134&forum=2&0discussing)

Probably much of the same info as ToSeek's article.

[spelling!!!]

<font size=-1>[ This Message was edited by: SpacedOut on 2002-04-23 11:29 ]</font>

Azpod
2002-Apr-23, 05:18 PM
One thought regarding this topic: if black holes don't decay, and aren't a true singularity, what will happen if we are successful at our attempts at creating this object in the lab? Could it be created by colliding heavy particles at high speeds using future generation colliders? Or would such an attempt fail, but fail in such a way that would lend support for the existance of this type of black hole?

God forbid it succeeds, creates a BH that doesn't evaporate that falls through the lab floor!

Ring
2002-Apr-24, 02:36 PM
On 2002-01-23 17:04, Wiley wrote:
I agree with you. The term "singularity" obviously comes from the mathematical definition of "singularity", which is non-analytic. So its not the function that is undefined but its derivative. (Both |x| and 1/|x| are singular at x = 0.)

My guess is the same as yours: when the equations become singular, it indicates you're bumping up against the limit of the theory.


Wiley, I'm afraid you've lost me here. Singular points can be either analytic or non-analytic, depending on whether there're regular or irregular. Plus, the charge density or mass density of an electron is a Dirac delta function. Are you saying that a black hole singularity would have to be a non-analytic, non delta function, singularity?