CH10 - Chapter 10 The Deaths of Stars Evidence that Stars...

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The Deaths of Stars Chapter 10
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Evidence that Stars Die When all the nuclear fuel in a star is used up, gravity will win over pressure and the star will die. High-mass stars will die first, in a gigantic explosion, called a supernova .
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Evolution off the Main Sequence: Expansion into a Red Giant Hydrogen in the core completely converted into He: H burning continues in a shell around the core He Core + H-burning shell produce more energy than needed for pressure support Expansion and cooling of the outer layers of the star Red Giant “Hydrogen burning” (i.e. fusion of H into He) ceases in the core
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A Main Sequence Star
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Burnout: core is pure He Main Sequence Turnoff
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The Coulomb (Electromagnetic) Barrier Like charges repel He nucleus = 2 protons + 2 neutrons
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Inert He core Main Sequence Turnoff
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G Gravity Pressure Hydrostatic Equilibrium
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A Main Sequence Star
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A Main Sequence Star
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H-burning shell Main Sequence Turnoff
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H-burning shell Inert He core Main Sequence Turnoff
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Main Sequence Turnoff Pressure from H-burning pushes envelope out
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Pressure from H-burning pushes envelope out Stellar envelope expands and cools: red giant phase
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A Red Giant Star H-burning shell Inert He core Not to scale!
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A Red Giant to Scale
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The Sun as a Red Giant (Image: Nick Strobel, astronomynotes.com)
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Betelgeuse Imaged With HST
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Expansion onto the Giant Branch Expansion and surface cooling during the phase of an inactive He core and a H- burning shell The Sun will expand almost up to the Earth’s orbit!
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Degenerate Matter Matter in the He core has no energy source left. → Not enough thermal pressure to resist and balance gravity → Matter assumes a new state, called Degenerate Matter Pressure in degenerate core is due to the fact that electrons can not be packed arbitrarily close together and have small energies. Electron energy
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Red Giant Evolution He-core gets denser and hotter until the next stage of nuclear burning can begin in the core: He fusion through the “triple-alpha process”: 4He + 4He → 8Be + γ 8Be + 4He → 12C + γ H-burning shell keeps dumping He onto the core. The onset of this process is termed the Helium Flash.
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A Red Giant Star H-burning shell Inert He core Not to scale!
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Inside a Red Giant Core Helium ash falls on degenerate core
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Inside a Red Giant Core
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Inside a Red Giant Core
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Inside a Red Giant Core
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Inside a Red Giant Core Helium Flash
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Evidence for Stellar Evolution: Star Clusters Stars in a star cluster all have approximately the same age! More massive stars evolve more quickly than less massive ones. If you put all the stars of a star cluster on a HR diagram, the most massive stars (upper left) will be missing!
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High-mass stars evolved onto the giant branch Low-mass stars still on the main sequence Turn-off point HR Diagram of a Star Cluster
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Estimating the Age of a Cluster The lower on the MS the turn-off point, the older the cluster
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This note was uploaded on 11/22/2011 for the course PHY 121 taught by Professor Weinstein during the Fall '08 term at SUNY Buffalo.

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CH10 - Chapter 10 The Deaths of Stars Evidence that Stars...

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