On the structure of Accretion Disks with Outflows

TL;DR

This paper develops a hydrodynamic model of accretion disks with outflows, revealing that outflows are common and stronger in slim disks, with disk structures depending on key physical parameters, aligning with recent simulations.

Contribution

It introduces a self-similar, spherical coordinate-based hydrodynamic model to analyze accretion disk structures and outflows, extending previous analytical and numerical studies.

Findings

Outflows are prevalent in various accretion disk types.

Slim disks exhibit stronger outflows due to advection and radiation pressure.

Disk structure varies significantly with input parameters.

Abstract

In order to study the outflows from accretion disks, we solve the set of hydrodynamic equations for accretion disks in the spherical coordinates ($r\theta\phi$) to obtain the explicit structure along the $\theta$ direction. Using self-similar assumptions in the radial direction, we change the equations to a set of ordinary differential equations (ODEs) about the $\theta$-coordinate, which are then solved with symmetrical boundary conditions in the equatorial plane, and the velocity field is obtained. The $\alpha$ viscosity prescription is applied and an advective factor $f$ is used to simplify the energy equation.The results display thinner, quasi-Keplerian disks for Shakura-Sunyaev Disks (SSDs) and thicker, sub-Keplerian disks for Advection Dominated Accretion Flows (ADAFs) and slim disks, which are consistent with previous popular analytical models. However, an inflow region and an outflow region always exist, except when the viscosity parameter $\alpha$ is too large, which supports the results of some recent numerical simulation works. Our results indicate that the outflows should be common in various accretion disks and may be stronger in slim disks, where both advection and radiation pressure are dominant. We also present the structure dependence on the input parameters and discuss their physical meanings. The caveats of this work and possible improvements in the future are discussed.