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Fraser
2005-Sep-22, 07:22 PM
SUMMARY: To have the current elements in the Universe, cosmologists believe there had to be several generations of stars, building up heavier and heavier elements. But what did that first generation of stars look like? They were probably huge, weighing 50-500 times the mass of the Sun. They lived quickly and then died as massive supernovae that seeded the surrounding space with heavier elements forged during this explosion. They could even be the source of gamma ray bursts, which are the most powerful known explosions in the Universe.

View full article (http://www.universetoday.com/am/publish/finding_first_stars.html)
What do you think about this story? post your comments below.

antoniseb
2005-Sep-22, 07:35 PM
It IS possible that some of the first stars were smaller than 50-500 times the mass of the Sun in the same way that a stellar nursery these days produces both massive stars down to brown dwarfs. If a nearly pure Hydrogen/Helium star can't ignite, there should be some relatively cold hulks floating around out there.

Don Alexander
2005-Sep-23, 02:32 AM
I guess so, antoniseb.

But they would be almost impossible to find. Small, light, not really emitting energy... Black dwarfs.

Being in a binary system is triply important for a Pop III star to become a GRB:

1. Mass loss removes the Red Supergiant atmosphere so that the jet isn't quenched.
2. Mass transfer kann increase the rotation of the star - a rapidly rotating black hole is essential for the Blandford-Znajek mechanism (powering the jets via angular momentum removal of the black hole, wich is coupled magnetically to the accretion disk).
3. Without mass loss, the Pop III star will not explode as a hypernova but as an even more powerful pair-production supernova, which leaves no remnant at all - thus no GRB.

Quite a complicated subject.

Greg
2005-Sep-23, 04:54 PM
Whether or not Swift finds these Pop III grbs has huge implications for our understanding of the early universe. Any data regarding this early era would be of great value considering that we have so little data now and thus no proof of what was going on then, just theories.

snowflakeuniverse
2005-Sep-25, 04:40 AM
It is important to recognize that population III stars have been assumed to exist only to explain the observation of “metals” in galaxies. They were not predicted in advance and their alleged existence has only come after the discovery in very young galaxies.

It my professional opinion as an engineer that type III stars cannot exist. Any system that has positive feed back characteristics tends to self-destruct. The feed back cycle would be.
1. A minor increase in the energy output increases the pressure in the core of the star.
2. The increase in the pressure causes the surrounding matter/plasma to be displaced outward.
3. The out rush of matter drops the pressure in the stars core.
4. The decrease in the pressure reduces the energy production
5. The matter that was displaced outward no longer has any pressure keeping it displaced so it “falls” back to the core.
6. Once the matter/plasma “falls” back to the core the pressure increases causing an increase in energy production.
The cycle keeps repeating over and over and if the amount of mass involved is large enough, eventually the star will explode.

Is there any evidence of a cyclic variation of energy output from a star composed mostly of Hydrogen and Helium? Yes. Variable stars contain far fewer “metals” than a main sequence star.

It is important for the core of a star to have an Iron core to provide stability. Any increase in core pressure will cause Iron to fuse to form heavier atoms, such as gold, uranium etc. This absorption of energy limits the feed back cycle described above.

(Also, according to my Uniform Expansion theory type III stars are not needed to explain the production of “metals” early in the evolution of the universe.)

Snowflake

Greg
2005-Sep-26, 04:42 AM
Snowflake,
I like your depiction and reasoning behind why these early stars would have been variable in nature. However, I do not see how, if this is true, that would preclude Pop III stars from existing. In theory they would indeed have been short-lived (lasting only a few million years at best) and exploded quickly, perhaps as a result of the very mechanism you describe.

The model of the early universe that I like the best is one that is alot smaller with a much greater mass density than today's universe. Matter was precipitating out of the ISM as the universe cooled just about everywhere. This would relatively quickly pool into denser and denser clouds until clusters of the these stars began to form. Centralizing more matter would have the effect of pulling more gas towards it from the surrounding ISM. It is easy for me to see how concentrating matter in shis fashion would snowball and quickly form large galaxies that we see today.

The heavy elements that we see today had to come from somewhere. Unless you wish to rework some fundamental aspects of the early (inflationary) universe and say that they precipitated out of the early ISM. This by no means is an easy or simple undertaking. If you have done so or you are referring to such a body of work, then please feel free to enlighten us with a reference so that we can read about it. I doubt that you would be able to fit any such explanation reasonably into a post of less than several pages.

snowflakeuniverse
2005-Sep-26, 09:42 PM
Hi Greg
Thanks for the response. Regarding my post that early stars with little “metalicity” would most likely variable stars you said
“However, I do not see how, if this is true, that would preclude Pop III stars from existing.”

Before I progress too far, it is important to note that any opinion from me on this issue is from outside the mainstream
The following link may yield more conventional explanations
http://www.aavso.org/vstar/vsots/winter05.shtml

You will find a bit more detail about the physical process by which Cepheid variable stars are believed to vary and some discussion on more energetic variable stars. It is described as a process occurring in the atmosphere rather than in the core, as was presented in my post. (Not all variable stars are Cepheid, and the more energetic variable star present some issues as to the process of energy production.).

Based upon the observed variable stars, it appears that there is a limit to size. As you suggest, the size limitation may be because the surrounding density of gas is insufficient to create such monsters today, This is the mainstream perspective. It is my opinion that the reason we do not see these massive stars is that they are just too unstable to exist. If these stars were possible, it seems that there would still be pockets of gasses shoved together from previous stars to reform such monsters somewhere near the cores of galaxies, none are observed.

You also pointed out that,
“The heavy elements that we see today had to come from somewhere. Unless you wish to rework some fundamental aspects of the early (inflationary) universe and say that they precipitated out of the early ISM. This by no means is an easy or simple undertaking. If you have done so or you are referring to such a body of work, then please feel free to enlighten us with a reference so that we can read about it. I doubt that you would be able to fit any such explanation reasonably into a post of less than several pages .”

Yes, you are right, I am proposing a “fundamental” explanation of the source of metals. And yes you are right that it would take more than a post of several pages.

I have posted most of the development of the theory in the “Against the Mainstream” forum. The basic gist of the theory is that the expansion of spacetime is truly uniform, meaning that even matter is uniformly expanding with the passage of time. A main prediction of the model is that the effect of gravity becomes a function of time. (If the Earth were 1/2 it’s present diameter, the effect of gravity on the surface would increase 4 times).

This model changes the big bang somewhat in that if we “run the clock backwards” instead of galaxies converging to one point or singularity, each galaxy will maintain it’s proportional distance from each other. (Using the balloon analogy, draw galaxies on a balloon and deflate the balloon, the proportional distance between each galaxy (10 galactic diameters) will remain the same. In this model, matter enters the universe at each galaxy with a given spatial separation, multiple “singularities” or spinning “threads”. This extremely dense appearance of matter at the cores of forming galaxies results in very rapid star evolution, resulting in the production of the metals observed today.

All local measures of distance and time keep their proportional measure, but from an historical perspective it is possible to see evidence of the increased effect of gravity and faster clock rates.

Snowflake

Greg
2005-Sep-28, 04:20 AM
I think some of your ideas about cepheid variables are worth considering and exploring regarding potential size limitations for early stars. Like it or not the popular theories about the evolution of the early universe appear to be full of unexplained gaping holes as the real data we need to validate these models is now coming in. Just today there was a very interesting article about a huge galaxy fully formed only 800 myrs after the big bang. My own feeling is that there may be some fundamental reworking of theories/models of the early universe in order to incorporate this new data.

I do agree that your ideas of the universe are far from mainstream. That leaves you with a huge uphill battle to fight in order to gain acceptance. All the more reason to carefully outline and delineate your ideas and provide a precise model to explain them. Any good theory of course will make predictions that can be proven by experimentation which is the benchmark for gaining acceptance beyond it looking good on paper (ie relativity). At a glance your ideas seem to be a variation on string theory, but I have not seen your threads on the other forum yet. There are a multitude of well worked out string theory based models out there yearning for acceptance, but have yet to be validated by a shread of proof unique to those theories, at least not yet. Even the current version big bang theory is out on a limb, so to speak, with predictions of dark matter and dark energy yet to be validated by any evidence (at least not yet.)

The specific problem with metallicity is that the current understanding of stellar evolution provides a convienent means of producing and distributing heavy elements via supernovas. Alot of evidence about the distribution of metals in stars around our galaxy and nearby galaxies seems to support this. It is therefore easy to extrapolate this backwards in time, and that much harder to accept an alternative source of heavy elements.