Two Types of Magnetohydrodynamic Sheath Jets

TL;DR

This paper proposes a magnetohydrodynamic model explaining the formation of double-layered astrophysical jets, identifying two solution types that correspond to different galaxy classifications and describing their physical characteristics.

Contribution

It introduces a novel MHD framework that explains the formation of spine-sheath jet structures and distinguishes two solution types linked to galaxy classifications.

Findings

Two main MHD solution types for sheath jets are identified.

One type describes marginally bound jets with decreasing temperature.

The other describes isothermal jets accelerated by MHD forces.

Abstract

Recent observations of astrophysical jets emanating from various galactic nuclei strongly suggest that a double layered structure, or a spine-sheath structure, is likely to be their common feature. We propose that such a sheath jet structure can be formed magnetohydrodynamically within a valley of the magnetic pressures, which is formed between the peaks due to the poloidal and toroidal components, with the centrifugal force acting on the rotating sheath plasma is balanced by the hoop stress of the toroidal field. The poloidal field concentrated near the polar axis is maintained by a converging plasma flow toward the jet region, and the toroidal field is developed outside the jet cone owing to the poloidal current circulating through the jet. Under such situations, the set of magnetohydrodynamic (MHD) equations allows two main types of solutions, at least, in the region far from the footpoint. The first type solution describes the jets of marginally bound nature. This type is realized when the jet temperature decreases like viral one, and neither the pressure-gradient nor the MHD forces, which are both determined consistently, cannot completely overcome the gravity even at infinity. The second type is realized under an isothermal situation, and the gravity is cancelled exactly by the pressure-gradient force. Hence, the jets of this type are accelerated purely by the MHD force. It is suggested also that these two types correspond, respectively, to the jets from type I and II radio galaxies in the Fanaroff-Riley classification.