The inner-workings of a star

[Tylorious]

Stars are some of the most interesting phenominal objects in the universe to me. I don't think you can look at a star, realize what it's actually doing, and not be impressed. But I am wondering if there is a possibility that we don't actually know what is happening inside it. The theory is pretty strong (For those of you who don't know the theory look up "nuclear fusion in stars"), but I can't help but think about the fact that there is absolutely no way to know if it is true. What do you guys think?

[AdmiralCheez]

A lot of the aspects of the stellar fusion theories make sense, like the whole "where do the elements come from" stuff. Some of the other theories are a bit outlandish, I think. Like the ones saying that anti-matter is created in the cores of stars. Or the ones saying that photons take hundreds of years to reach the surface of a star from the core, and then accelerate to light speed. Then again, the laws of physics get kind of wacky when dealing with that much energy, pressure, and gravity. That's where you get things like black holes and neutron stars.

Unfortunately, there's no real way to prove most of those theories either way because any probe sent to observe the core of a star would be disintegrated long before it ever reached the surface. Still, it's fun to think about.

[factotum]

This is one of those situations where, as far as I'm aware, every prediction made by the model corresponds to what we actually see--we can even detect the neutrinos emitted by the Sun, albeit with great difficulty. One therefore has to ask, if we're wrong about what's going on in there, what *is* going on that matches the experimental evidence so closely? It's a lot easier to assume that the common idea of stellar formation and lifecycle is correct unless you find discrepancies that don't fit (or even disprove your theory).

[Tebryn]

You should take a listen to this song (http://www.youtube.com/watch?v=ENJKo5jqjUw).

[Finlam]

You should also read this (http://what-if.xkcd.com/73/) because it's FUN!

[BWR]

You should take a listen to this song (http://www.youtube.com/watch?v=ENJKo5jqjUw).

Not bad, but I prefer the classics (http://www.youtube.com/watch?v=uLpu2UP3rGI).

[Tebryn]

Not bad, but I prefer the classics (http://www.youtube.com/watch?v=uLpu2UP3rGI).

Can't go wrong with that one either.

[mucat]

The theory is pretty strong (For those of you who don't know the theory look up "nuclear fusion in stars"), but I can't help but think about the fact that there is absolutely no way to know if it is true. What do you guys think?
We're confident that our models of stellar fusion are accurate, because we can study stars of a huge variety of masses and at every stage of their lifetimes, and their behavior matches quite well with what the models predict. What humans can't do, of course, is watch a single star go through all the phases of its life, because that would take a hell of a long time. :smallwink:

Also, we have never observed a low-mass star (say, half the Sun's mass or less) in the late stages of its life, because the lifetime for those stars can be far longer than the current age of the universe; all the ones that exist now are young'uns.


A lot of the aspects of the stellar fusion theories make sense, like the whole "where do the elements come from" stuff. Some of the other theories are a bit outlandish, I think. Like the ones saying that anti-matter is created in the cores of stars.
The only antimatter that's created in stellar fusion are positrons (the antimatter version of electrons.) When two protons fuse, the weak nuclear force converts one of them into a neutron, with a positron as one of the byproducts. This isn't outlandish or speculative; it's what ALWAYS happens in fusion reactions, including ones we run in labs on Earth.

The positrons don't last long, since there are plenty of electrons present in the core of the star. The positron and an electron annihilate and release gamma rays, which contribute to the overall energy produced by the fusion process.



Or the ones saying that photons take hundreds of years to reach the surface of a star from the core, and then accelerate to light speed.
It's not that they "accelerate" to light speed, exactly...just that the photons are not travelling in a straight line as they diffuse their way out from the star's core. The plasma is dense enough that photons are bouncing around randomly like balls in a pachinko machine. When they finally reach the surface, they're free to stream away in a straight line.



Then again, the laws of physics get kind of wacky when dealing with that much energy, pressure, and gravity. That's where you get things like black holes and neutron stars.
Yes, and for the end-stage behavior of the supermassive stars that form neutron stars and black holes, we really are uncertain how good our models are. We can observe supernovas and get a general idea of how that final collapse works, and we can sometimes see evidence of the neutron stars and black holes that remain afterwards, but the actual collapse is so energetic and so far out of equilibrium that it's crazy-hard to model! (And even if we could travel there to make close-up observations, our instruments probably wouldn't survive long... :smalleek:)

[AdmiralCheez]

The only antimatter that's created in stellar fusion are positrons (the antimatter version of electrons.) When two protons fuse, the weak nuclear force converts one of them into a neutron, with a positron as one of the byproducts.



It's not that they "accelerate" to light speed, exactly...just that the photons are not travelling in a straight line as they diffuse their way out from the star's core. The plasma is dense enough that photons are bouncing around randomly like balls in a pachinko machine. When they finally reach the surface, they're free to stream away in a straight line.


Ah, right. That was the explanation for those. I remember learning about that in an Astronomy class, but that was years ago. I guess they're not so outlandish when I remember the details. Now, things like M-Theory are still mind-boggling to me, and I don't think I'll ever quite get a grasp on that.