Three-Dimensional Evolution of the Parker Instability under a Uniform Gravity

Abstract

Using an isothermal MHD code, we have performed three-dimensional, high-resolution simulations of the Parker instability. The initial equilibrium system is composed of exponentially-decreasing isothermal gas and magnetic field (along the azimuthal direction) under a uniform gravity. The evolution of the instability can be divided into three phases: linear, nonlinear, and relaxed. During the linear phase, the perturbations grow exponentially with a preferred scale along the azimuthal direction but with smallest possible scale along the radial direction, as predicted from linear analyses. During the nonlinear phase, the growth of the instability is saturated and flow motion becomes chaotic. Magnetic reconnection occurs, which allows gas to cross field lines. This, in turn, results in the redistribution of gas and magnetic field. The system approaches a new equilibrium in the relaxed phase, which is different from the one seen in two-dimensional works. The structures formed during the evolution are sheet-like or filamentary, whose shortest dimension is radial. Their maximum density enhancement factor relative to the initial value is less than 2. Since the radial dimension is too small and the density enhancement is too low, it is difficult to regard the Parker instability alone as a viable mechanism for the formation of giant molecular clouds.

8 pages of text, 4 figures (figure 2 in degraded gif format), to appear in The Astrophysical Journal Letters, original quality figures available via anonymous ftp at ftp://ftp.msi.umn.edu/pub/users/twj/parker3d.uu or ftp://canopus.chungnam.ac.kr/ryu/parker3d.uu

References in corpus (1)

• The MHD Kelvin-Helmholtz Instability II: The Roles of Weak and Oblique Fields in Planar Flows

Cited by in corpus (22)

• Theory of Star Formation
• Regulation of Star Formation Rates in Multiphase Galactic Disks: Numerical Tests of the Thermal/Dynamical Equilibrium Model
• The Magnetic Rayleigh-Taylor Instability in Three Dimensions
• Three-Dimensional Simulations of Parker, Magneto-Jeans, and Swing Instabilities in Shearing Galactic Gas Disks
• Luminous and Dark Matter in the Milky Way
• Nonlinear Evolution of the Magnetohydrodynamic Rayleigh-Taylor Instability
• High accretion rates in magnetised Keplerian discs mediated by a Parker instability driven dynamo
• Incorporation of cosmic ray transport into the ZEUS MHD code. Application for studies of Parker instability in the ISM
• Burial of the polar magnetic field of an accreting neutron star. II. Hydromagnetic stability of axisymmetric equilibria
• Angular Momentum in Giant Molecular Clouds. I. The Milky Way
• The Parker Instability in 3-D: Corrugations and Superclouds Along the Carina-Sagittarius Arm
• The Parker Instability in Disk Galaxies
• Three-dimensional Simulations of the Parker Instability in a Uniformly-rotating Disk
• Formation of Interstellar Clouds: Parker Instability with Phase Transitions
• The Parker Instability in a Thick Galactic Gaseous Disk: I. Linear Stability Analysis and Nonlinear Final Equilibria
• The Parker Instability in a Thick Gaseous Disk II: Numerical Simulations in 2D
• The Effect of the Random Magnetic Field Component on the Parker Instability
• Resistive MHD simulations of the Parker instability in galactic disks
• 3D Magneto-Hydrodynamic Simulations of Parker Instability with Cosmic Rays
• Introduction to Faraday tomography and its future prospects
• Parker Instability in a Self-Gravitating Magnetized Gas Disk: I. Linear Stability Analysis
• The Influence of the Gravitational Acceleration on the Supernova-Driven P arker Instability