RE: Article: "Sun is Mostly Iron, Not Hydrogen"

From: Reason (
Date: Thu Jan 10 2002 - 03:14:11 MST

---> jeff davis

> > You can fuse iron atoms, but the reaction is
> > endothermic. So when this
> > happens, the star core cools. There are other
> > nuclear processes
> > involving iron too, and all are endothermic and
> > hence tend to cool the
> > star, causing it to compress.
> I'm no astrophysicist either,...but consider. Earth
> has an iron core. The asteroid belt has asteroids
> that are largely iron.
> Iron is abundant in the solar system.

Ok, so far I've managed to avoid biting my own leg off *and* entering this
thread. Now it's one or the other.

I'm an astrophysicist. My first Masters was based on work on metallicity in
stars (pop III stuff) and acting as translator for eccentric old stellar

The composition and behavior of stellar bodies is well understood. Has been
for fifty years -- everything after 1950 has been refinements in the math,
understanding in how phase changes propagate through stellar plasmas,
electromagnetic field and energy transport behavior in the atmosphere of
stars, physics of supernovae. You still look at 1920's groundwork if you
want to get work done on how the bulk of a star hangs together.

Stars are very, very different from planets. Plasma works very differently
from the other forms of matter. The laws of physics, even in very simple
form, lead quite clearly to non-intuitive behavior inside stars, the results
of which are easily observed at the various emission layers, burning zones
and phase changes. Change, even slightly, what is going on in an inner layer
of the star, and you'll see potentially very divergent results at the
surface -- some of the governing equations are non-linear.

When modelling a star, only two things matter: 1) how much mass it has, 2)
how much stuff that isn't hydrogen or helium it has; these two items operate
in conjunction to determine density, pressure (due to radiation and
otherwise) and equilibrium points. A non-collapsed, stable star is seriously
metalled up if it has 2% of it's mass as metals (= anything that isn't H or

As I recall, the sun hasn't started it's helium burning phase in earnest
yet, nor has it exhausted the hydrogen in the core. This means that the core
of the sun is still pretty much H/He. I forget the exact percentages arrived
at through simulation. Go google.

> The question of the putative iron core of the sun was
> a lot of fun to mull over.

A much more interesting question (up until last year in any case) would be
how to prove that there isn't a black hole at the core of the sun,
surrounded by a fairly large sphere of high-energy, very low density plasma.


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