Just a quick comment:
Temperature isn't a 'real' quantity, but rather a statistical measurement.
Simply put, temp is just the average energy or motion of the particles. When particles have more than a specific amount of energy, they can no longer hold certain bonds.
Example:
Beyond 100 c, the average water molecule has too much energy to stay connected with neighbooring water molecules (so it becomes a vapor instead of a liquid).
Likewise at higher energies (corresponding to the temp of the sun), electrons have too much energy to stay bonded to a specific atom, so the nuclei and electrons all fly around in what we call a plasma.
I've got no idea how much energy is required to prevent the strong force from holding stable nuclei together, but I'm sure there is a point where that happens.
Regarding radius from a region of high temp - it doesn't matter what the temp is nearby, only right at your location (well, until that nearby temp heats up your area). Think of a thermos - you can hold them just fine, your hand just an inch from boiling hot water, with no problem. Of course, there aren't any materials that could insulate from super nova temps, since they would quickly be broken down into plasma.