3D Magneto-Hydrodynamic Simulations of Parker Instability with Cosmic Rays

TL;DR

This paper uses 3D magneto-hydrodynamic simulations to explore how cosmic rays influence Parker instability in the interstellar medium, revealing that cosmic-ray diffusion accelerates instability growth and affects cloud formation.

Contribution

It introduces the first detailed 3D MHD simulation of Parker instability incorporating cosmic-ray diffusion effects in the ISM.

Findings

Cosmic-ray diffusion increases the growth rate of Parker instability.

Cosmic rays enhance dense cloud formation in the ISM.

Cloud shapes depend on initial perturbation conditions.

Abstract

This study investigates Parker instability in an interstellar medium (ISM) near the Galactic plane using three-dimensional magneto-hydrodynamic simulations. Parker instability arises from the presence of a magnetic field in a plasma, wherein the magnetic buoyant pressure expels the gas and cause the gas to move along the field lines. The process is thought to induce the formation of giant molecular clouds in the Galaxy. In this study, the effects of cosmic-ray (CR) diffusion are examined. The ISM at equilibrium is assumed to comprise a plasma fluid and a CR fluid at various temperatures, with a uniform magnetic field passing through it in the azimuthal direction of the Galactic disk. After a small perturbation, the unstable gas aggregates at the footpoint of the magnetic fields and forms dense blobs. The growth rate of the instability increases with the strength of the CR diffusion. The formation of dense clouds is enhanced by the effect of cosmic rays (CRs), whereas the shape of the clouds depends sensitively on the initial conditions of perturbation.