Chapter 9 The Main Sequence

Four fundamental forces of nature All four forces have to do with the Sun

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

Quantum tunneling

energy region where the reaction is more likely to take place Gamow Peak: energy region where the reaction is more likely to take place Can’t tunnel through Coulomb barrier From http://nu.phys.laurentian.ca/~fleurot/fusionrate/ The Gamow peak is the product of the Maxwell-Boltzmann distribution with the tunnelling probability of the nuclei through their Coulomb barrier. This is the energy region where the reaction is more likely to take place: at higher energies, the number of particles becomes insignificant while at lower energies the tunnelling through the Coulomb barrier makes the reaction improbable. The dimension of the Maxwell-Boltzmann distribution and of the Gamow peak is keV-1, while the tunnelling probability is dimensionless. Few particles

Another view of Gamow peak

One of 3 branches of proton-proton chain

CNO cycle: C, N O atoms act as catalysts

T-dependence of pp chain and CNO cycle

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”