Angular momentum transport by thermal emission in black hole accretion disks

摘要

We calculate the amount of angular momentum that thermal photons carry out of a viscous black hole accretion disk, due to the strong Doppler shift imparted to them by the high orbital velocity of the radiating disk material. While thermal emission can not drive accretion on its own, we show that along with disk heating it does nonetheless result in a loss of specific angular momentum, thereby contributing to an otherwise viscosity-driven accretion flow. In particular, we show that the fraction of the angular momentum that is lost to thermal emission at a radius r in a standard, multi-color disk is ∼0.4r_s/r, where r_s is the Schwarzschild radius of the black hole. We briefly highlight the key similarties between this effect and the closely related Poynting-Robertson effect (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)