Mestel cooling gives for white dwarfs of the same core composition and envelope opacity

PHYSICS · Subjective · Fermi University Physics · Astrophysics & Cosmology · Stellar structure, energy generation and evolution · Stellar death and compact objects

Stars from the Inside, Ch White dwarfs: the relativistic polytrope, the Chandrasekhar mass and a cooling clock

Problem

Mestel cooling gives tcool∝M5/7L−5/7t_{\rm cool} \propto M^{5/7}L^{-5/7} for white dwarfs of the same core composition and envelope opacity. Mestel's law puts a 0.6 M⊙0.6\,M_\odot carbon-oxygen white dwarf at L=1.0×10−4 L⊙L = 1.0\times10^{-4}\,L_\odot after a cooling time of 4.4 Gyr4.4\,\mathrm{Gyr}. Use this to estimate the cooling age of a 1.0 M⊙1.0\,M_\odot carbon-oxygen white dwarf observed at L=1.0×10−3 L⊙L = 1.0\times10^{-3}\,L_\odot.

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