Gravitational stability of a cylindrical plasma with an azimuthal and an axial magnetic field

TL;DR

This paper analyzes how combined axial and azimuthal magnetic fields influence the gravitational stability of filamentary plasma clouds, revealing that strong azimuthal fields can induce instability in large, realistic current-carrying filaments.

Contribution

It introduces an analytic model incorporating azimuthal magnetic fields into the stability analysis of filamentary clouds, providing new insights into their physical mechanisms and stability criteria.

Findings

Azimuthal magnetic fields contribute to the virial equilibrium.

Strong azimuthal fields can cause instability in large filamentary clouds.

The model offers a computationally inexpensive stability guidance.

Abstract

We consider the gravitational stability of a current carrying filamentary cloud in the presence of both axial and azimuthal magnetic fields using a simple analytic model. The azimuthal magnetic field is shown to give rise to a new contribution, dictated by Ampere's law, in the corresponding virial equation for magnetohydrodynamic equilibrium. From this we obtain a computationally inexpensive guidance on the gravitational stability of current carrying filamentary clouds. The approach not only provides a fresh insight into the essential physical mechanisms involved, but also demonstrates clearly that, for sufficiently large and yet astronomically realistic currents, the azimuthal magnetic field can cause filamentary clouds to undergo instability.