Evolution of Massive Stars
To understand the r-process, p-process, and the rest of the nucleosynthesis that results from the deaths of massive stars in supernovae and the deaths of neutron stars in neutron star mergers, we must begin long before the explosions that distribute these materials into the interstellar medium with the final stages of the lives of massive stars. For stars below a critical mass — approximately 8 Solar masses — degeneracy in the CO core prevents the ignition of carbon burning. These low-mass stars end their lives as cooling CO white dwarves with masses less than 1.1 solar mass,surrounded by the envelope they ejected in their AGB star winds.For much more massive stars, from perhaps 11 solar masses, up to roughly 100 solar masses, hydrostatic carbon, neon, oxygen, and silicon burning leave a core composed of iron, cobalt, nickel, and neighboring species, commonly referred to as the iron-peak nuclei.