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short lived, UV photons from hot, exposed core excite the shells of gas & create fluorescence. hot core is supported by the electron degeneracy pressure, cools to become a white dwarf. white dwarf slowly cools over billions of y ear to become a black dwarf summary of sun’s life: pre main seq: no fusion, powered by gravity. main seq: H burning in core. red giant branch: H burning in shell surrounding He core. horizontal branch: He burning in core, H burning in shell. ASG: H & He burning in shells surrounding CO core. planetary nebula: no fusion, hot core emits uv radiation & gas shell fluoresces. white dwarf: no fusion, white dwarf cools & becomes black dwarf carbon on earthwas created by fusion of helium in core of horizontal branch star & fusion of helium in shell of AGB star. death of high mass stars initial stages are similar to those of sun like star: main sequence (H fuses to He in core) → red super giant (contracting He core, H fused to He in shell around core) → blue super giant (He fuses to C & O in core, H fuses to He in shell. stars more massive than 8m(sun( will go through all stages of nuclear fusion. fusion takes less & less & less time as the energy source becomes less efficient. end product of Si burning: iron group elements-- Cr, Mn, Fe, Co Ni. no more energy generation when iron appears, star has exhausted all nuclear fuel photodisintegration:ironcore contracts, releases gravitational energy, density & temp increase. when temp is high enough, energetic photons are abundant, photon energy is high enough to break . reverse nuclear fusion. energy is absorbed which accelerates core contraction. inverse of H burning, photodisintegration undoes what star does for its entire life neutronization.at high density, electrons generate large pressure (electron degeneracy pressure) that helps counteract gravity but the pressure has a limit & cannot supply the gravity of the massive iron core. electrons are energetic enough to trigger inverse decay. neutronization depletes core of electrons & their supporting degeneracy pressure. Carry large amount of energy out of star.implosion:photodisintegration & neutronization remove almost all pressure in the core which causes the core to collapse, or impose. outer layers of star lose contact with core. the nuclear material eventually becomes still & the strong nuclear force becomes repulsive (neutron degeneracy pressure), core rebounds & becomes a neutron star. shock waves go through core → high temp causes photodisintegration → shock stalls because photodisintegration steals energy → neutrinos heat the gas & cause shock wave to move → super nova explosion when the outer layers are ejected at high speed. elements heavier than iron are produced in shock wave & are ejected into interstellar medium classifying supernovae: no H lines = type 1. si lines = type 1a (explosion of white dwarfs. no si lines (core collapse-- explosion of massive stars). he line = type 1b. mno he lines = type 1c. h lines = type 2 (core collapse-- explosion of massive stars) core collapse:energy released = to energy sun released in 80 years. peak luminosity is comparable to moderate sized galaxy. ejects stella material into interstellar medium. heavy elements are ejected. elements heavier than iron are made during super nova explosion.