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Since stars are an ideal example of macroscopic objects, is their evolution determined by their initial mass and metallicity?

Are there any non-trivial random internal processes going on that may significantly affect a star's development and eventual fate? (It is quite evident that capture of another star or a brown dwarf is an external, exogenous event.)

EDIT/clarification: I'm looking for things that may shorten/extend the lifetime of a star beyond the "norm" prescribed by nuclear physics/gravity, change its composition, surface temperature. Solar flares/quakes and other instabilities come to mind first.

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    $\begingroup$ Exactly what do we mean by "non-trivial"? That any fusion happens at all is a quantum event with probability not 1; it's just ridiculously close to 1 by sheer magnitude (your (almost) 'ideal macroscopic object'). The death of (large mass) stars is also based on quantum events with probabilities technically not 1 (and is very fast), so it is technically possible for a star not to die in a way it really ought to by sheer chance. It's just so improbable it's highly unlikely to happen anywhere in the observable universe. Is that trivial? $\endgroup$ – zibadawa timmy Jan 5 '15 at 22:14
  • $\begingroup$ @zibadawatimmy Yes, I would say those are good examples of trivial by any definition. Even if your question was "Is this likely to ever happen anywhere in the known universe?" the answer is still no with a trivial degree of uncertainty. Trivial means information that is of little importance or value. $\endgroup$ – Mark Bailey Jan 5 '15 at 22:33
  • $\begingroup$ @zibadawatimmy You up for answering this? astronomy.stackexchange.com/questions/8472/… $\endgroup$ – HDE 226868 Jan 6 '15 at 0:22
  • $\begingroup$ en.wikipedia.org/wiki/Richtmyer%E2%80%93Meshkov_instability $\endgroup$ – Deer Hunter Jan 8 '15 at 7:37
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If you want to go into truly random stuff, you should look into quantum. The internal processes inside a star are not random, however they are bviously undetectable. Some factors other than mass and metallicity are temperature of the original dust cloud, or angular velocity. The temperature obviously affects the brightness, while the angular velocity will affect the gravity. I am not an expert, but I'd assume that any minor perturbation inside the star could cause a butterfly effect and result in, say, solar flares, so on average there would be stars who would be losing more mass than others with no particular reason. I assume there would be other factors linked with more complicated physics, too.

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  • $\begingroup$ Right, but does this change the course of stellar evolution? Deer Hunter did say "significantly affect". $\endgroup$ – HDE 226868 Jan 5 '15 at 21:56
  • $\begingroup$ Well, I'd assume that temperature and angular kinematics do actually play a major role, but then again those phenomena are not random. The minor fluctuations can be attributed to chance, but they can't cause much of a variation. I guess it depends on one's definition of 'significantly'. $\endgroup$ – L.R. Jan 5 '15 at 22:02
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This is not an answer that stems from vast cosmological knowledge and experience, but from an intuitive mathematical understanding of stochasticity. I would point out that stars do not have the visual appearance of stability or a predictable nature. They are churning, belching balls of nuclear plasma. On a macroscopic scale, I would expect stability to look like smoother surfaces or uniform activity. Any object that you might describe as "constantly exploding" or even "on fire", or particularly, "undergoing nuclear reaction", I would ordinarily say involves an element of chance.

The flare and CME activity of our Sun is governed by a roughly 11 year cycle. But it's not exactly old faithful. The activity of the Sun follows patterns, but they are noisy patterns. However, even though stars are the very image of chaos to our view, it seems that they are actually quite predictable. One reason is that they live in a vacuum. Literally. Or very near a vacuum. Particularly since your question eliminates consideration of external interactions, we are talking about stars like ours, surrended by mostly a lot of nothing. So when plasma erupts out of the star at less than escape velocity, we know that ultimately that plasma is coming right back home to the star. It's not going to smear onto some other object. And the goop from other objects isn't going to smear onto the star.

Second, the time-scale of a star's evolution is enormous. Imagine watching a timelapse movie of our Sun where each frame of the movie shows the average (mean) appearance of the sun over 100 eleven-year solar cycles. Now you would see something that looks quite smooth, stable. And you could watch that movie of a stable glowing ball all day long without seeing any dramatic change. (Assuming 24 frames per second, watching the movie all day long would take you through 2.3 billion years of the Sun's life.) Because the timescale in question is so long, the bubbling, churning, and exploding we see on our timescale amounts to unfathomably insignificant blips in a stable, predictable, burn process.

In general, any stochastic (random) event reproduced enough times, in the same way (with the same kind of randomness), will lead to stable, predictable outcomes. A man has solar panels on his roof. Some days are sunny, and some are overcast. Some days the panels get covered up completely in snow. But over the course of a year, we can still predict approximately how much power his panels will produce with about 98% accuracy, assuming there is no external influence, like the house burning down.

So yes, excluding external interactions, if you know the total mass and composition of a star at conception, it makes sense that the chaos and noise of the atomic fireball would have a net zero effect on the outcome.

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