I begin work on my project for thermal physics this week. It's due Friday--I know, I am running late. Sometimes that's the way things work.
Requirements: 3 pages of work/writing/calculations "on a problem." Not very specific!
What I intend to do: Rederive neutron stars in some fashion. Or just degenerate stars. Or maybe just play along with the equilibrium equation of a star and see what happens.
In any given star you've got something pushing out (radiation pressure) and something pulling in (gravitational force/unit area = gravitational pressure). For a star like our sun, these are about equal--the material's trying to fall into the center of the sun due to gravity, but it keeps running into other stuff and, eventually, combining with that other stuff to make new stuff + energy/light, which pushes everything back out.
Now for all stars, eventually you're going to run out of stuff that can combine and make energy. You've started with something light, probably hydrogen or at most helium, and run hydrogen into more hydrogen to make helium, and helium into hydrogen to make, oh, Lithium or something like that. And then you run that into something else and so on until you end up with iron.
Now the problem with iron is that when you run iron atoms together, or iron + a hydrogen, or iron + anything else, it doesn't release energy when they smack together and stick. Instead, it starts to cost energy to smack those things together and make them stick. The star doesn't want to do this, because it's lazy, like all things. It doesn't want to put in the work. Or perhaps more imagine it that it is not human so it can't have human emotions like "motivation" and "inspiration." there's nothing around to make it do that extra work to make those things stick.
What does that mean? Well eventually you're going to have lots of iron, but it's not going to be making new things + energy, so the radiation pressure, the energy that was pushing it out, falls off and disappears. But gravity is definitely still working, and it is still going to try to pull things together.
Now here is where things get fuzzy. I know you get the following: some sort of large boomish sort of event, followed by some sort of condensing of the core. The star repels its envelope, the hot outer gas and material. Whether it does this via going supernova (and blowing up the rest of the star, too), or just by pushing the envelope off and letting the rest of the core fall in on itself (to become a white dwarf or a neutron star or a black hole, depending on its mass), I am not sure. So I don't know precisely how this works. Why would it push that stuff off first? why not just let all of that stuff fall in? Observational evidence says it doesn't (otherwise how could something small like the earth get big nuclei like those for cobalt or iron? we're not hot enough to make them--we must have "rolled up" remnants of blown-off star bits)
UPDATE: well, investigating. We'll see what happens