ASTRON 1101 Lecture Notes - Lecture 23: Photodisintegration, Neutrino, Main Sequence
23 Oct 2016
School
Department
Course
Professor
Document Summary
When silicon runs out in a massive star"s core, the inert fe-ni core has m = 1. 5 msun, r = rearth = There are no more fusion sources of energy. Electron degeneracy pressure is inadequate to maintain hydrostatic equilibrium. As the core is compressed, its temperature rises. Photodisintegration occurs: high energy photons melt large nuclei back into helium nuclei, reversing post-main sequence fusion. Then, higher-energy photons melt helium nuclei into protons and neutrons, reversing post-main-sequence fusion. Then, higher-energy photons melt helium nuclei into protons and neutrons, reversing main sequence fusion. The density is high enough for protons to capture free electrons and form neutrons and neutrinos. 1. 5 msun of iron contains ~1057 protons, and thus produces 1057 neutrinos. With photodisintegration and neutrino emission draining thermal energy, the core collapse is fast. After 0. 1 second, the density of the collapsing ball of neutrons reaches 200 million tons/cm3. This is the same density as an atomic nucleus.
