Chapter 9 The Main Sequence Four fundamental forces

Chapter 9 The Main Sequence

Four fundamental forces of nature

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

Gamow Peak: energy region where the reaction is more likely to take place Can’t tunnel through Coulomb barrier 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”