This diagram shows a simplified (not to scale) cross-section of a massive, evolved star (with a mass greater than eight times the Sun.) Where the pressure and temperature permit, concentric shells of Hydrogen (H), Helium (He), Carbon (C), Neon/Magnesium (Ne), Oxygen (O) and Silicon (Si) plasma are burning inside the star. The resulting fusion by-products rain down upon the next lower layer, building up the shell below. As a result of Silicon fusion, an inert core of Iron (Fe) plasma is steadily building up at the center. Once this core reaches the Chandrasekhar mass, the iron can no longer sustain its own mass and it undergoes a collapse. This can result in a supernova explosion.
R. J. Hall
User:Rursus