Lecture 20

Lecture 20 - Today (Mon.) in Astro 3 Cell phones off now,...

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Today (Mon.) in Today (Mon.) in Astro Astro 3 3 z Cell phones off now, please z Midterm #2 results: Í Grade scale slightly more lenient than MT1 Í Return scantrons at end of class like MT1 z Reminder: online quiz due tonight 10 p.m. z The Plan: Í This week, Mon. labs only Í Today Chapter 12 “Stellar Evolution” Í Weds: Neutron stars and black holes Kepler’s supernova: in X-rays
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Units of Chapter 12: Stellar Evolution 9 Leaving the Main Sequence 9 Evolution of a Sun-like Star 9 The Death of a Low-Mass Star Evolution of Stars More Massive than the Sun Supernova Explosions Observing Stellar Evolution in Star Clusters The Cycle of Stellar Evolution The Helix nebula: an old star that has shed its outer layers. 650 ly = 207 pc
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12.2 Evolution of a Sun-like Star Even while on the Main Sequence, the composition of a star’s core is changing:
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12.2 Evolution of a Sun-like Star As the fuel in the core is used up, the core contracts ; when it is used up the core begins to collapse. Hydrogen begins to fuse outside the core:
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12.2 Evolution of a Sun-like Star The red giant stage on the H-R diagram The core shrinks, but the outer layers of the star expand and cool : The center of the star gets hotter. As a result, the star expands so much that its surface temperature falls.
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12.2 Evolution of a Sun-like Star Stage 10 on the H-R diagram: Once the core temperature has risen to 100,000,000 K, the helium in the core starts to fuse . The helium flash : Helium begins to fuse extremely rapidly; within hours the enormous energy output is over, and the star once again reaches equilibrium
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12.2 Evolution of a Sun-like Star Stage 11: Back to the giant branch As the helium in the core fuses to carbon
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Lecture 20 - Today (Mon.) in Astro 3 Cell phones off now,...

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