The magnetohydrodynamic instability of current-carrying jets

TL;DR

This paper analyzes the stability of astrophysical jets with complex magnetic fields, revealing that such jets are inherently unstable to non-axisymmetric perturbations regardless of the magnetic field strength configuration.

Contribution

It provides a linear stability analysis of jets with combined azimuthal and axial magnetic fields, showing persistent instability across different field strength ratios.

Findings

Jets are always unstable to non-axisymmetric perturbations.

Instability occurs for all azimuthal wave numbers when axial field is weaker.

Growth rates saturate at low azimuthal wave numbers for weaker axial fields.

Abstract

Magnetohydrodynamic instabilities can be responsible for the formation of structures with various scales in astrophysical jets. We consider the stability properties of jets containing both the azimuthal and axial field of subthermal strength. A magnetic field with complex topology in jets is suggested by theoretical models and is consistent with recent observations. Stability is discussed by means of a linear analysis of the ideal magnetohydrodynamic equations. We argue that in azimuthal and axial magnetic fields the jet is always unstable to non-axisymmetric perturbations. Stabilization does not occur even if the strengths of these field components are comparable. If the axial field is weaker than the azimuthal one, instability occurs for perturbations with any azimuthal wave number $m$, and the growth rate reaches a saturation value for low values of $m$. If the axial field is stronger than the toroidal one, the instability shows for perturbations with relatively high $m$.