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Fraser
2005-Apr-12, 05:35 AM
SUMMARY: Black holes... you know. Cosmic singularities that can contain the mass of billions of stars like our Sun. Where the pull of gravity is so strong, nothing, not even light can escape their fearsome grasp. They're the source of much discussion, indirect observation and science fiction speculation. But according to George Chapline from Lawrence Livermore National Laboratory in California, they don't exist. Instead we have dark energy stars, which are connected to that mysterious force accelerating the expansion of the Universe.

Listen to the interview: Dark Energy Stars (5.1 mb)

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Svemir
2005-Apr-12, 06:24 AM
I read it yesterday and thought: why not?
Would it provide the mechanism for Arp's quasar ejection theory?
Next time somebody will put the dark energy in an atom or a neutron :P
The article defies the existence of Black Holes (which I like), but the same day the article that defies existence of dark energy came to daylight (I like it too :-))
http://www.arxiv.org/PS_cache/astro-ph/pdf...504/0504192.pdf (http://www.arxiv.org/PS_cache/astro-ph/pdf/0504/0504192.pdf)

Max
2005-Apr-12, 10:11 AM
I had a theory last year that black holes don't exisit , but No one listens to me...

http://www.localwebpubs.co.uk/tigmas/bhp.htm

Guest_mike
2005-Apr-12, 10:23 AM
The idea of dark energy stars is ridiculous(see his original work http://arxiv.org/abs/astro-ph/0503200).
There is physicially no need for such objects because the doubts which leads George Chapline to formulate the concept of dark energy stars is solved by lots of physicists without proposing a possible but unproved phase transition of the collapsing matter.
For example by Hawking and Asthekar and many others,by introducing dynamical or apparent horizons instead of event horizons. See (http://arxiv.org/abs/gr-qc/0504038 or http://arxiv.org/abs/gr-qc/0504029 ).
The other reason why his theory is very unfirm is that nobody knows exactly what dark energy is.It is also possible that no dark energy exist (http://arxiv.org/abs/astro-ph/0503553) .

ravik521
2005-Apr-12, 09:51 PM
[FONT=Geneva] [COLOR=green]I think black holes do exist. It is also possible about dark energy stars. But which one is true? There is such a thing called dark energy in space. That is why our universe is expanding faster. The dark energy is causing this. But, does the same thing apply to stars? :huh:

Greg
2005-Apr-13, 05:02 PM
An interesting idea, but I do not think it makes alot of sense from the perspective of galaxy evolution. Where does this dark energy come from and how does it get concentrated in teh center of a galaxy? At least we have a good mechanism for how black holes form and how they ended up at the center of galaxies. The same caoont be said of dark energy stars. What strikes me as interesting is how the concepts of dark energy and dark matter are all inimately interrelated with or understanding of gravity, which by no means is complete as yet.

Svemir
2005-Apr-20, 06:53 AM
To Max:
I read your proposal ( I can't call it a theory)
"Missing matter" in galaxies can't be stored in Black Holes (as you self pointed 95%).
Super Massive Black Holes are resident in the galaxy center and we are missing matter in outer edges of the galaxies.
Even with small Black Holes (starlike masses) it's not possible to account for missing matter. There are simply not enough of them. Therefor, some people are looking for brown dwarfs to account for "missing matter", they outnumbers the black holes.
Another thing, Black Holes don't exist.
There are people with far better understanding of General Relativity Theory who proved that existence of Black Holes in Hawking's sence (singularity + event horison) is in conflict with GRT!
Last year Stephen Hawking admitted that he was wrong about Black Holes.
Think of it, his entire life and lives of many of his disciples wasted.
Black Holes, when first described in terms of GRT by Hawking et. al. were so pesimistic, they ate everything and nothing couldn't escape their deadly hug.
It strongly defies our way of thinking, having such thing in mind leads to depression.
Then, Hawking himself put something optimistic in his Black Holes, Hawking radiation (never observed likewise singularity and event horison).
Suddenly, Black Holes were not so dangerous anymore, they vaporized, they vanished.

But his solution (on paper) was not compatible with Quantum Theory, Black Holes were losing all information about their formation, and he never recived Nobel Prize.
As someone on this forum put it, his a great thinker, he just thinks in the wrong direction.
Let's go back to people with a view that Black Holes can't exist (not me or you, we just feel it can't be right):
1. Yilmaz. In his Theory of Relativity (YRT), Black Holes don't exist.
2. Abhas Mitra, he is a proponent of Einsteins Relativity (ERT), but nevertheless, he proved mathematicly that Black Holes don't exist if ERT is applied properly.
And guess what.
He's got a replay on this guy, George Chapline's, idea of Dark Energy Stars.
http://www.arxiv.org/PS_cache/astro-ph/pdf...504/0504384.pdf (http://www.arxiv.org/PS_cache/astro-ph/pdf/0504/0504384.pdf)

aatt
2005-Jun-14, 03:07 PM
What about the Gravastar theory and the Holostar one? Both say singularities don't exist. The latter theory even say that we don't need any dark energy in the universe: inside a holostar an accelerating Hubble espansion should form! our whole universe could be such a strange object too ... and we are not crushed at all! ;) I also read a paper some years ago, where it was argumented that, if graviton has just a very little mass, then a layer thick just a Planck length should form upon the events horizon, avoding any time paradox. I am not expert to understand which among several models is the best, but I have many doubts now that "classical" Hawking-Penrose black holes (with singularities) can never exist. If you say a BH can evapore leaving only a "nake singularity", I can't believe that, and i find silly any "Cosmic Censor" invented ad hoc to avoid that. - bye, aatt-

M Petri
2005-Jun-18, 10:23 AM
Originally posted by aatt@Jun 14 2005, 03:07 PM
What about the Gravastar theory and the Holostar one? Both say singularities don't exist. The latter theory even say that we don't need any dark energy in the universe: inside a holostar an accelerating Hubble espansion should form! our whole universe could be such a strange object too ... and we are not crushed at all! ;)
Hi aatt,

The "holostar theory" is not really a theory. Rather, the holostar space-time is an exact, spherically symmetric solution of the Einstein field equations. In fact, it is probably the simplest spherically symmetric solution possible. As such it is interesting to study. And it has some interesting properties.

But the fact that there is an interesting, simple solution to the field equations which appears to have the potential to explain many phenomena that we find in the "real world" does not mean that one can say that singularities do not exist. Holostar and black holes are exact solutions of the field equations. That is all one can say for the moment. The problem with the field equations is, that they admit many solutions. But most solutions are unphysical. For some solutions this is quite easy to see, for other solutions this is more difficult. In order to decide, whether the compact objects in some binary systems or at the centers of galaxies are black holes, gravastars, holostars or something different, we need compare the predictions of the various exact solutions with the phenomena that we observe. One big problem, however, is, that the predictions do not differ substantially [the deviations are of order 10^-20 to 10^-80 for compact objects of solar mass] for an observer, who observes a compact object from the outside. Therefore, at least at today's state of knowledge, it seems impossible to distinguish a black hole from a gravastar or a holostar by measurements from the outside.

The only viable possibility seems to be, to try to get into such an object. The problem is, if we actually manage get in, it is easy to see from the equations of motion, that we practically have no chance to report our findings back to an outside observer. But what, if we ourselves, are already inside such a compact object? The compact object must be very large, at least the size of the universe. And the interesting thing is, that, in fact, the interior holostar solution appears to explain some observed phenomena that we encounter in our universe pretty well.

A geodesically moving observer will see an isotropic Hubble-type expansion from his frame of reference. The luminosity redshift relation of from the recent supernova-data is explained fairly well, too. The holostar interior has negative pressure, e.g. something similar to what we now call "dark energy" [without really knowing what dark energy is] etc. etc.

But although the agreement between predictions of the "holostar theory" [which is nothing else than Einsteins general theory of relativity with string type matter] and observations raises some hopes, that it might eventually lead to a better understanding of the universe and the compact objects at the centers of galaxies, there still is a severe problem with the holostar. Its interior matter has a so called string equation of state. So one would presume, that all of its interior matter consists out of strings. This is similar to what string theorists assume: According to string theory the basic building blocks of matter should be strings. But it is quite difficult to relate these theoretical ideas/predictions to what we find in the real world. Is an electron, a neutrino, a photon really a string structure? If we take the holostar equations seriously, the interior string type matter should have an active gravitational mass-density which is exactly zero. But evidently electrons, baryons etc. have mass, although their masses are very very small, m = 10^-23 - 10^-20 in "natural" units. So the prediction of zero active gravitational mass seems to fail, although the particle masses are close to zero, so that the failure is not catastrophic. But what shall we do about these small masses? Are they quantum corrections? So there still is much to be found out.

Also you are not entirely correct in your assessment, that an observer falling into a holostar will not be crushed. Well, he will not be crushed to a point, that is true. But his likely fate is, that he will travel right to the center [that will take a long, long time]. The closer he gets to the center, the hotter and denser will his surroundings become. When he finally reaches the center he will encounter a very hot region of space-time of nearly Planck-density, Planck-Temperature. He will not be crushed [because the Heisenberg uncertainty principle forbids him to get closer to the center than roughly a Planck length] but he will certainly not stay intact either in this furnace. Most likely he will be broken apart into his fundamental constituents [strings?] and then these constituents will travel back the way he came [most likely on a different radial ray than the ray he came in]. When he travels outward, the temperature gets lower, the density gets lower, so that the fundamental constituents can condense into particles, the particles can form nebula, suns, planets etc. In fact, after he has travelled for a proper time of of order of the age of our universe, he will have reached a radial distance r=10^61 r_Pl [where r_Pl is the Planck length]. At this position the holostar interior, viewed from the perspective of a geodesically moving observer coming from the center, does not look very much different, on a large scale, from what our universe looks now. And the history of such an observer is very similar to our history. The further you look back into the past, the hotter it gets. So the holostar has the appearence of a Big Bang, as well. But in contrast to the Big Bang of the well known Friedman-Robertson-Walker (FRW) models, his journey does not start out from a singularity with infinite matter-density, infinite pressure, infinite temperature etc. but "just" from a region of Planck-density, Planck-temperature.

Therefore the "holostar theory" can shed some doubts on the points of view, that singularities are really necessary to explain the phenomena that we observe. But the mere fact that we have an interesting exact solution of the field equations is far from being able to "prove" that singularities do not exist. Such a proof is not possible. No scientific theory can be proved rigorously, because it will always have to be based on some - more or less reasonable - assumptions, which have to be postulated. These assumptions, or rather a particular theory based on these assumptions, can only be falsified. One can check a theory's predictions. One can even check whether its logical structure is free of inconsistencies. But even if a theory is internally consistent, one never knows whether someday, sometime a clever person will find a new theory, which explains the phenomena even better.

M Petri