Accretion Alfvén radius ($r_{\mathrm{Alf}}$)

The accretion Alfvén radius estimates where the magnetic stress of an accreting star competes with inflow stress and disrupts an approximately Keplerian disk. It is distinct from the Alfvén critical radius of an outgoing stellar wind. A dipole and a free-fall pressure estimate give the characteristic $B_{\ast }^{4/7}{\dot{M}}^{-2/7}$ scaling; the numerical coefficient depends on flow geometry, and an inferred radius inside the star is outside the model's domain.