A neutron star 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 neutron star accretor has mass

M = 1.4\,M_\odot

and radius

R = 11\,\mathrm{km}

. ((a)) Compute the accretion efficiency

\eta = GM/(Rc^2)

. ((b)) Compute the Eddington luminosity

L_{\rm Edd} = 4\pi GMm_pc/\sigma_T

. ((c)) Compute the Eddington accretion rate

\dot M_{\rm Edd} = L_{\rm Edd}/(\eta c^2)

M_\odot\,\mathrm{yr^{-1}}

, and say in one sentence why it is smaller than the white dwarf value of

7.5\times10^{-6}\,M_\odot\,\mathrm{yr^{-1}}

for the same Eddington luminosity scaling.