An O-type main-sequence star has mass and radius

PHYSICS · Subjective · Fermi University Physics · Astrophysics & Cosmology · Radiation, radiative transfer and stellar atmospheres · Stellar structure, energy generation and evolution

Stars from the Inside, Ch Energy transport and the complete stellar model

Problem

An O-type main-sequence star has mass M=20 M⊙M = 20\,M_\odot and radius R=8.0 R⊙R = 8.0\,R_\odot. Its photospheric opacity is dominated by electron scattering, κˉR=0.034 m2 kg−1\bar\kappa_R = 0.034\,\mathrm{m^2\,kg^{-1}} (appropriate to hydrogen mass fraction X=0.7X=0.7). Using the surface gravity g=GM/R2g = GM/R^2 and the grey-atmosphere result Pph=23g/κˉRP_{\rm ph} = \tfrac{2}{3}g/\bar\kappa_R, find the photospheric pressure.

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