The dynamics of internal working surfaces in MHD jets

TL;DR

This paper develops an analytic model to understand how toroidal magnetic fields influence internal working surfaces in radiative jets, revealing magnetic dominance over gas pressure and effects like axial pinching or broadening.

Contribution

The paper introduces a novel analytic model for magnetic effects on internal working surfaces in jets, validated by numerical simulations.

Findings

Magnetic forces dominate over gas pressure within jet working surfaces.

Magnetic fields can cause axial pinching or broadening of the internal structures.

Model predictions are confirmed by axisymmetric numerical simulations.

Abstract

The dynamical effects of magnetic fields in models of radiative, Herbig-Haro (HH) jets have been studied in a number of papers. For example, magnetized, radiative jets from variable sources have been studied with axisymmetric and 3D numerical simulations. In this paper, we present an analytic model describing the effect of a toroidal magnetic field on the internal working surfaces that result from a variability in the ejection velocity. We find that for parameters appropriate for HH jets the forces associated with the magnetic field dominate over the gas pressure force within the working surfaces. Depending on the ram pressure radial cross section of the jet, the magnetic field can produce a strong axial pinch, or, alternatively, a broadening of the internal working surfaces. We check the validity of the analytic model with axisymmetric numerical simulations of variable, magnetized jets.