Time-dependent magnetohydrodynamic self-similar extragalactic jets

TL;DR

This paper models extragalactic jets using time-dependent magnetohydrodynamic equations, revealing a natural formation of collimated polar lobes and embedded plasmoids consistent with radio observations.

Contribution

It introduces a self-similar MHD model for jets that explains magnetic lobe structures and embedded plasmoids in a finite plasma pressure regime.

Findings

Polar lobe dominates in intensity and collimation.

Embedded secondary plasmoids with alternating magnetic fields.

Model aligns with observed radio intensity islands.

Abstract

Extragalactic jets are visualized as dynamic erruptive events modelled by time-dependent magnetohydrodynamic (MHD) equations. The jet structure comes through the temporally self-similar solutions in two-dimensional axisymmetric spherical geometry. The two-dimensional magnetic field is solved in the finite plasma pressure regime, or finite $\beta$ regime, and it is described by an equation where plasma pressure plays the role of an eigenvalue. This allows a structure of magnetic lobes in space, among which the polar axis lobe is strongly peaked in intensity and collimated in angular spread comparing to the others. For this reason, the polar lobe overwhelmes the other lobes, and a jet structure arises in the polar direction naturally. Furthermore, within each magnetic lobe in space, there are small secondary regions with closed two-dimensional field lines embedded along this primary lobe. In these embedded magnetic toroids, plasma pressure and mass density are much higher accordingly. These are termed as secondary plasmoids. The magnetic field lines in these secondary plasmoids circle in alternating sequence such that adjacent plasmoids have opposite field lines. In particular, along the polar primary lobe, such periodic plasmoid structure happens to be compatible with radio observations where islands of high radio intensities are mapped.