2. Thermonuclear runaway in degenerate stars a) (15 points) We discussed in class how main sequence stars undergoing nuclear fusion are stable to small changes in their core temperatures. Explain qualitatively why this is not the case for nuclear fusion taking place in degenerate stars. b) (10 points) The result is a thermonuclear runaway. In white dwarfs, this can occur if 12C fusion is triggered in the core. Calculate the total energy output of the resulting fusion, assuming that the entire mass of a 1Msun white dwarf is synthesized from 12 to 56 Ni, which releases 0.1% of Mc in energy. How does this compare to its gravitational binding energy? Does a Type Ia supernova leave any bound remnant behind? c) (10 points) In stars with MS2MSun, core helium fusion starts under degenerate conditions, resulting in a sudden "flash" of energy release. For a Sun-like star of M 1Msun and R = 1Rsun, what fraction of the total mass can be consumed in 4He fusion (energy release of 6 10-4Mc) without exploding the star?