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##### Chapter 9 The Main Sequence

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**Chapter 9**The Main Sequence**Hydrostatic equilibrium: negative feedback loop**• If core T drops, • fusion rate drops, • core contracts • heats up • If core heats up, • fusion rate rises • core expands • cools down**Main sequence stars are modeled as concentric spherical**shells in hydrostatic equilibrium Mass element dm Constant density Inward force = outward force**Binding energy holds a nucleus together:BE = total mass of**each individual nucleon - mass of nucleus**The Coulomb barrier:**1 in 1085 particles has the energy to cross it**Wave function**Probability distribution**Gamow Peak:**energy region where the reaction is more likely to take place Can’t tunnel through Coulomb barrier Few particles**Solar neutrino problem:**Early searches for solar neutrinos only found ~1/3 the expected number of neutrinos**Solar neutrino problem:**Early searches for solar neutrinos only found ~1/3 the expected number of neutrinos Neutrinos apparently can change form. According to nuclear physics theory, this means they must have mass! “flavor oscillation”**Super-Kamiokande in Japan.**• 1 km underground (in a mine) • 11,000 light-detectors in/around a pool of water • Neutrino can (rarely) interact with a proton • A particle is produced that moves faster than the speed of light in water • Causes an optical “sonic boom”