Radiation Drag Effects in Black Hole Outflows from Super-critical Accretion Disks via Special Relativistic Radiation Magnetohydrodynamics Simulations

TL;DR

This study uses special relativistic radiation magnetohydrodynamics simulations to analyze super-critical accretion disk outflows, revealing how radiation drag limits outflow velocity and influences collimation and energy distribution.

Contribution

First detailed simulation showing radiation drag's role in limiting outflow speed and shaping outflow structure in super-critical accretion disks.

Findings

Outflow velocity saturates around 0.3-0.4c due to radiation drag.

Total kinetic and photon luminosities are approximately equal to the Eddington luminosity.

Slower outflows carry most of the kinetic energy, with velocity regulated by force balance.

Abstract

By performing 2.5-dimensional special relativistic radiation magnetohydrodynamics simulations, we study the super-critical accretion disks and the outflows launched via the radiation force. We find that the outflow is accelerated by the radiation flux force, but the radiation drag force prevents the outflow velocity from increasing. The outflow velocity saturates around 30-40% of the light speed around the rotation axis, since then the flux force balances with the drag force. Our simulations show that the outflow velocity is kept nearly constant in the regime of \dot{M}_{BH} ~ 100-1000 L_{Edd}/c^2, where \dot{M}_{BH} is the mass accretion rate, L_{Edd} is the Eddington luminosity, and c is the light speed. Such a faster outflow is surrounded by a slower outflow of ~ 0.1c. This velocity is also determined by force balance between the radiation flux force and the radiation drag. The radiation drag works to collimate the slower outflow in cooperation with the Lorentz force, although the faster outflow is mainly collimated by the Lorentz force. The kinetic energy is carried by the slower outflow rather than by the faster outflow. The total kinetic luminosity of the outflow as well as the photon luminosity is ~ L_{Edd}, almost independent of the mass accretion rate.