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

Big bang

[Anonymous Coward]

If this turns out to be true, the discovery will also cast a shadow of doubt over the big bang theory which also features a singularity.

still the same

[nomadic]

And I thought traditional black holes were wacky enough. According to this, it's possible that our entire universe is contained within one of these gravastars.

I've never heard of this site, but I must admit that was an extremely well-written article; they shoved a lot of physics in it but maintained a really high level of clarity (though it seems to based on a New Scientist article, so they may have just lifted passages from there).

Re:still the same

[ndevice]

that idea is nothing new. some people think that it's possible that the entire universe is within the event horizon of a black hole. Another way of looking at it is the question of is the universe open, closed, or static.

Since a black hole is something that nothing escapes out of the event horizon of (disregarding hawking radiation), if the universe is closed and collapses on itself, by definition, we are inside a big black hole, and if it's open, it's not.

Need to shine a little experimental light.

[ArcSecond]

All this sounds a bit like philosophers arguing about how many angels can dance on the head of a pin. Unfortunately, the lack of an empirical solution (just go an look at one) is holding us back from really nailing down the true nature of "black holes".

What I do find interesting is that this gravastar model, like the black hole model, implies that the universe and black holes/gravastars are similar in nature: that they belong to the same class of objects. It is a wonderful puzzle to look into a black hole wondering "what's IN there", when the answer might be something that has qualities similar to the life-cycle of our own cosmos.

Until we get some solid predictions about ways to differentiate one from the other, this is going to be a purely theoretical debate. Hopefully someone can advance the debate into the experimental realm soon. Maybe the new gravitational observatories can "shed some light" on this shadowy subject. ;)

You can't have both..

[ender81b]

Ok, my physics is a little rusty but.. this doesn't make sense.

As the article mentions - you just CANT go around violating the second law of thermodynamics like they do (i.e. for a gravstar to form it must 'lose' entropy).

According to these guys the spherical outer shell (a standing gravitational wave) would balance out with the incoming matter. Now waiiit just a minute. Eventually the matter on the shell would exceed the force of the inner substance supporting it - then what do you have? They say that it would cause the sphere to wiggle and radiate away energy - well every struture has it's limits, what would happen when, say, a more massive gravstar impacts a less massive gravstar? Or two gravstars of equal mass impact each other?

Just b/c our understanding of physics breaks down at the singularity doesn't mean it does not exist (remember we can't describe in physical terms just what the first few picoseconds of the big bang where like - the physics just can't cope with the amount of matter/energy involved).

Now, we can *never* actually observe a black hole (God Abhors a Naked Singularity) which doesn't mean they don't exist.
"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." TO do so the matter woudl have to exceed the speed of light. Right.

More wierd stuff...

[metlin]

These problems stem from the fact that our Universe is actually very different from the one that Schwarzschild considered. If we're to produce a proper description of the Universe we live in, Einstein's classical theories need to be meshed together with what we know about the quantum laws governing the behavior of fundamental particles and fields.

Ofcourse. And that is what the Unified Field Theory is all about. In fact, if only gravitons could be proved to exist, then there is a very high probability of the existence of the UFT. In fact, there are just 6 universal constants which need to be meshed in with their corresponding DEs to get the UFT up and running. Which, I'd say, seems simpler than what these guys may have to offer. Are these guys trying imply that UFT does not exist?

They believe that in the extreme conditions of a collapsing star, space-time undergoes a quantum version of a phase transition. The phenomenon is nothing new. The Nobel Prize for Physics in 2001 was awarded for the observation of just such an event in the lab: the transformation of a cloud of atoms into one huge "super-atom," a Bose-Einstein Condensate (BEC). This clump of atoms, which all share the same quantum state, forms at temperatures within a whisker of absolute zero.

In this context, are these people trying to say that the gravistar behaves as a BEC? That makes it a hell lot more complex because you will need really low temperatures, and adding more particles rushing to you at the speed of light increases the temperature and the entropy, both of which their theory goes against. Also Bosons (which are carrier particles, having an integer spin measured in the units of h-bar) would all possess exactly the same quantum state. So considering the existence of identical entities elsewhere, we could jump to any of these thingys just like that. Or any matter trapped in even one of these, could be spread across multiple copies of these entities.

The implications are really wierd, I somehow feel that Black Hole theories were a lot more plausible.

Re:More wierd stuff...

[Anonymous Coward]

If you have done any amount of tensor calculus & quantum physics related mathematics (which I'm
assuming you have), you'll know that Black Holes can be described with considerable ease in a
Riemann plane, than gravistars.

You seem to be confusing Riemannian manifolds (ND manifolds with metric structure) with Riemann planes (2D surfaces generated from complex functions).

1. You have submanifolds which would overlap as more matter gets in, and so the relativistic frame
would in itself be a function carrying many frames.

What the heck are you talking about? "Overlapping submanifolds"?? The authors aren't describing anything like that. "Frames carrying many frames?" You're babbling.

Now, you have a solution for these called Bertotti-Robinson Solution, and when these are
applied to a Black Hole, they work out just fine.

What does the Bertotti-Robinson solution have to do with anything being discussed here? It's just a universe with a uniform magnetic field.

Re:More wierd stuff...

[Anonymous Coward]

Btw, Schwarzschild Radius itself has been verified and proved by Chandrashekhar, for which he won
the Nobel Prize.

No. He proved a limiting mass for white dwarves. This happens before the Schwarzschild radius is reached, and none of his calculations involved event horizons or black holes.

There has been evidence from galaxies about the existence of EHs as observed by Chandra and
Hubble, independently.

True.

In fact, there is also evidence of tunneling in EHs which have been photographed.

Uh, no. There is no evidence of anything "tunneling" through an event horizon.

Re:More wierd stuff...

[SirYakksALot]

You don't *need* low temperatures to form a BEC. Low temperatures attack the velocity side of position/velocity uncertainty. High density could attack the position side.

Re:no singularity...

[(void*)]

When I posed this question to one of my physics professors at Caltech back in my student days, he came up with nothing better than that, either.

That in fact is a very good explanation for what is going on.

The "escape velocity" explanation is basically expressing an energy requirement. It is not insightful, like the light cone explanation becuase the light cone (when visuallized) shows you exactly which trajectories are possible. They all head towards the blackhole. The whole idea is that you cannot overtake the speed of light.

So why is the answer not satisfying? Being a physics TA, I have to understand the misunderstandings of students. It would be very helpful to me to understand why the answer is not satisfying.

Re:You can still get sucked in

[BlueUnderwear]

No, black holes are not solid. They are vacuum solutions. There is no matter at the horizon,

True, but I never claimed that (at least not for black holes)

there is no matter inside the horizon

That depends on your definition of matter. It's not matter in the classical sense, but rather severely degenerated (collapsed) matter. And concentrated in one point (the singularity). Then of course, there's also the philosophical question about whether it is legitimate to talk about what goes on inside the event horizon. After all, there is no way that we could possibly see what's inside (no light and no information gets out).

(Incidentally, gravistars, as described, aren't really hollow. Inside the "outer shell of gravitational energy" is a dense condensate.)

Maybe, I misread the article, but I understood it to mean that the condensate was on the shell.

Emil Mottola of the Los Alamos National Laboratory in New Mexico and Pawel Mazur of the University of South Carolina in Columbia think gravastars are cold, dense shells supported by a springy, weird space inside.

So what is this springy, weird space? Some special kind of "vacuum"? The condenstate?

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.

But if all matter is expelled towards the shell, wouldn't we end up with a "hollow" sphere? Hollow, except for the weird field, that is.

I hate "+5 Insightful" ratings for wrong answers...

And I hate self-righteous ACs.

Re:Your own reference seems to contradict you

[Dr. Manhattan]

Also, think for a moment that you (YANAAE) are disputing the word of an aerodynamics engineer...

Of course, if the traditional explanation for how a wing works were correct, planes would not be able to fly upside down.

But they can...

Re:You can still get sucked in

[flumps]

Please note that, and I quote:

It would be surrounded by a thin spherical shell composed of gravitational energy, a kind of stationary shock wave in space-time sitting exactly where the event horizon of a black hole would traditionally be.

I would say therefore that the gravitational energy is just that: gravitational energy, not some form of wierd mass surrounding it. Your scenario is bogus and would never happen :)