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lecture15 - Cinco de Mayo The Sun nuclear fusion(producing...

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Cinco de Mayo! The Sun! nuclear fusion (producing energy) energy transport in the sun hydrostatic equilibrium sun’s atmosphere
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Midterm Info Will be returned to your slots either today or Wednesday note that the scantrons will have the correct answer if you got it wrong and you have your exam! Curve will be emailed at that time.
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Sun’s Energy Sun’s luminosity: 3.90 x 10 26 W (recall: 1 Watt = 1 Joule/sec) What can produce this much energy? And for so long? the Earth is 4.56 Gyr old, so the sun must also be at least that old! Current gravitational contraction? that only produces energy for about 25 Myr Chemical energy? energy yield too low need to use up too many atoms to maintain the sun’s luminosity would only produce energy for about 10,000 years for the sun.
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Nuclear Power A result of Einstein’s special theory of relativity: Mass can be converted into energy: E = mc 2 E: energy (J) m: mass (kg) c: speed of light (m/s) A small amount of mass is converted to a lot of energy
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Nuclear Fusion in the Sun Center of the sun: central density: 1.6 x 10 5 kg/m 3 central temperature: 1.55 x 10 7 K yo ho it’s hot Atoms are completely ionized here so just a bunch of protons (H nuclei) and alpha particles (He nuclei) running around Center of the sun is hot and dense enough for nuclear fusion R < 0.25 R SUN Note: 94% of the Sun’s mass is in R < 0.5 R SUN
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Proton-Proton Chain Step 1: p + p D + ν + e + p: proton D: Deuterium nucleus (1 proton + 1 neutron) ( 2 H) ν : neutrino e + : positron (anti-electron) In this step, energy is released: in the neutrino
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