ASTR 1020 1st Edition Lecture 14 Outline of Last Lecture I. Star LivesA. Helium FlashB. Planetary NebulaeOutline of Current Lecture I. Star Lives: High-Mass StarA. Life StagesB. FusionC. High-Mass StarD. Supernova ExplosionE. Close Binary StarsF. Red GiantCurrent LectureI. Star Lives: High-Mass StarA. Life Stages 1. Main Sequence: H fuses to He in core 2. Red Supergiant: H fuses to He in shell around He core 3. Helium Core Burning: He fuses to C in core while H fuses to He in shell 4. Multiple Shell Burning: Many elements fuse in shells 5. Supernova leaves neutron star or black hole behindB. Fusion- H to He by the CNO Cycle - High-mass main sequence stars fuse H to He at a higher rate using carbon, nitrogen, and oxygen as catalysts - He fuses to C in core- Then He can fuse with C and heavier atomsC. High-Mass Star- A high-mass star can continue to fuse elements in its core right up to iron (“onion” like shells). - As heavier elements are fused, the reactions go faster and the stage is over morequickly. - A 20-solar-mass star will burn carbon for about 10,000 years, but its iron core lasts less than a day.- Iron is dead end for fusion because nuclear reactions involving iron do not release energyD. Supernova Explosion- Core collapse causes electrons to combine with protons, making neutrons and neutrinos - Neutrons collapse to the center, forming a neutron star - Outer layers bounce off core and are ejected into spaceE. Close Binary Stars- Mass transfer can radically change stars. Example: Algol (“eye of the Medusa”) - Began as a detached binaryF. Red Giant- As the more massive star became a red giant, it began mass transfer onto the gainer star.- Eventually the mass gainer became the more massive star, leaving the mass donor as a red subgiant. Algol
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