Relativistic Radiation Hydrodynamical Accretion Disk Winds

TL;DR

This paper develops a fully relativistic radiation hydrodynamics model to study accretion disk winds, revealing how wind speed and type depend on disk luminosity and radiative flux, with winds reaching relativistic speeds.

Contribution

It introduces a novel relativistic radiative hydrodynamics framework to analyze accretion disk winds, including the effects of relativistic speeds and gravitational fields.

Findings

Transonic winds pass through saddle points with speeds up to 0.8c.

Luminous disks produce always supersonic winds reaching near light speed.

Critical points and wind behavior depend on normalized radiative flux and enthalpy.

Abstract

Accretion disk winds browing off perpendicular to a luminous disk are examined in the framework of fully special relativistic radiation hydrodynamics. The wind is assumed to be steady, vertical, and isothermal. %and the gravitational fields is approximated by a pseudo-Newtonian potential. Using a velocity-dependent variable Eddington factor, we can solve the rigorous equations of relativistic radiative hydrodynamics, and can obtain radiatively driven winds accelerated up to the {\it relativistic} speed. For less luminous cases, disk winds are transonic types passing through saddle type critical points, and the final speed of winds increases as the disk flux and/or the isothermal sound speed increase. For luminous cases, on the other hand, disk winds are always supersonic, since critical points disappear due to the characteristic nature of the disk gravitational fields. The boundary between the transonic and supersonic types is located at around $\hat{F}_{\rm c} \sim 0.1 (\epsilon+p)/(\rho c^2)/\gamma_{\rm c}$, where $\hat{F}_{\rm c}$ is the radiative flux at the critical point normalized by the local Eddington luminosity, $(\epsilon+p)/(\rho c^2)$ is the enthalpy of the gas divided by the rest mass energy, and $\gamma_{\rm c}$ is the Lorentz factor of the wind velocity at the critical point. In the transonic winds, the final speed becomes 0.4--0.8$c$ for typical parameters, while it can reach $\sim c$ in the supersonic winds.