PHYSICS · Multi-part · Fermi University Physics · Nuclear Physics · Astrophysics & Cosmology · Stellar structure, energy generation and evolution
Stars from the Inside, Ch Thermonuclear energy generation: reaction rates, burning stages and the elements they make
Problem
Helium ignites at T=1.0×108K in two helium cores, one at density ρ=1.0×106kgm−3 and one at ρ=1.0×109kgm−3, both with μe=2. Triple alpha there has ν≈40.
((a)) Use Chapter 5's degeneracy boundary, Tdeg≈1.2×103(ρ/μe)2/3K with ρ in kgm−3, to decide whether the electrons in each core are degenerate.
((b)) Decide for each core whether the burning regulates itself or runs away, and say what the large ν does in each case.
((c)) For the core that regulates itself, find the fractional fall in temperature that undoes a 10 per cent excess in ϵ.