A white dwarf accretor has mass and radius .

PHYSICS · Multi-part · Fermi University Physics · Astrophysics & Cosmology · Stellar death and compact objects · Stellar death and compact objects

Stars from the Inside, Ch Accretion power: mass transfer, discs and the weighing of black holes

Problem

A white dwarf accretor has mass M=1.0 M⊙M = 1.0\,M_\odot and radius R=5000 kmR = 5000\,\mathrm{km}. ((a)) Compute the accretion efficiency η=GM/(Rc2)\eta = GM/(Rc^2), the fraction of the rest-mass energy of accreted matter radiated as it settles onto the surface. ((b)) Using LEdd=4πGMmpc/σTL_{\rm Edd} = 4\pi GMm_pc/\sigma_T (Thomson-scattering opacity, one proton per electron), compute the Eddington luminosity. ((c)) Hence compute the Eddington accretion rate M˙Edd=LEdd/(ηc2)\dot M_{\rm Edd} = L_{\rm Edd}/(\eta c^2), in M⊙ yr−1M_\odot\,\mathrm{yr^{-1}}.

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