Jet launching from accretion discs in the local approximation

TL;DR

This paper investigates jet launching mechanisms from accretion discs using local approximation models, highlighting how magnetic field strength influences mass loss rates and potential burst ejections.

Contribution

It introduces a simplified model and numerical simulations for jet launching in the local approximation, emphasizing the role of magnetic field strength and inclination.

Findings

Mass loss rate decreases rapidly with increasing magnetic field strength.

Quasi-steady solutions exist for strong poloidal magnetic fields suppressing MRI.

Rapid ejection bursts may occur if the magnetic field is appropriately configured.

Abstract

The acceleration of an outflow along inclined magnetic field lines emanating from an accretion disc can be studied in the local approximation, as employed in the computational model known as the shearing box. By including the slow magnetosonic point within the computational domain, the rate of mass loss in the outflow can be calculated. The accretion rates of mass and magnetic flux can also be determined, although some effects of cylindrical geometry are omitted. We formulate a simple model for the study of this problem and present the results of one-dimensional numerical simulations and supporting calculations. Quasi-steady solutions are obtained for relatively strong poloidal magnetic fields for which the magnetorotational instability is suppressed. In this regime the rate of mass loss decreases extremely rapidly with increasing field strength, or with decreasing surface density or temperature. If the poloidal magnetic field in an accretion disc can locally achieve an appropriate strength and inclination then a rapid burst of ejection may occur. For weaker fields it may be possible to study the launching process in parallel with the magnetorotational instability, but this will require three-dimensional simulations.