As a former astrophysics major:
Y'know, stars start out by burning hydrogen. That's nice and clean. Eventually, they start to burn other things. Metals. Yes, stars burn metals.
I wonder. Hmm...
Can post details on effects of metal on main sequence stars, and the order in which we believe stars burn those metals. In fact, here. Effects you can google on your own
but this is a nice list of what stars do in nucleosynthesis.
Hydrogen starts it off. After that it can synthesize Helium, Carbon, Oxygen, Neon, Magnesium, Silicon, Sulfur, Argon, Calcium, Titanium, Chromium, and Iron.
A star the size of ours can hit carbon. Heavier stars are required to heat, compress and thus synthesize the heavier elements.
Iron is not compressible. When a star's core runs out everything but iron, there's no more fusion. No more energy pushing outwards and countering gravity. Gravity takes over, and either wins (singularity) or gets 'splodied by the star's matter expanding outwards like it was all part of some gigantic, insanely tight spring (supernova).
Even heavier elements, like gold, are made when stars go boom. The force of the 'splody-ing can create all sorts of atoms.
</astro-tangent>
So. Wonder if the condition of the sun is linked to allomancy and/or the rise of the Lord Ruler?