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Lookup NU author(s): Dr Devika Tharakkal, Professor Anvar ShukurovORCiD, Dr Fred Gent, Dr Graeme Sarson, Andrew Snodin
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
We study the linear properties, nonlinear saturation and a steady, strongly nonlinear state of the Parker instabilityin galaxies. We consider magnetic buoyancy and its consequences with and without cosmic rays. Cosmic rays aredescribed using the fluid approximation with anisotropic, non-Fickian diffusion. To avoid unphysical constraintson the instability (such as boundary conditions often used to specify an unstable background state), nonideal MHDequations are solved for deviations from a background state representing an unstable magnetohydrostatic equilibrium.We consider isothermal gas and neglect rotation. The linear evolution of the instability is in broad agreement withearlier analytical and numerical models; but we show that most of the simplifying assumptions of the earlier workdo not hold, such that they provide only a qualitative rather than quantitative picture. In its nonlinear stage theinstability has significantly altered the background state from its initial state. Vertical distributions of both magneticfield and cosmic rays are much wider, the gas layer is thinner, and the energy densities of both magnetic field andcosmic rays are much reduced. The spatial structure of the nonlinear state differs from that of any linear modes. Atransient gas outflow is driven by the weakly nonlinear instability as it approaches saturation.
Author(s): Tharakkal D, Shukurov A, Gent FA, Sarson GR, Snodin AP, Rodrigues LFS
Publication type: Article
Publication status: Published
Journal: Monthly Notices of the Royal Astronomical Society
Year: 2023
Volume: 525
Issue: 4
Pages: 5597-5613
Print publication date: 01/11/2023
Online publication date: 31/08/2023
Acceptance date: 22/08/2023
Date deposited: 13/06/2024
ISSN (print): 0035-8711
ISSN (electronic): 1365-2966
Publisher: Oxford University Press
URL: https://doi.org/10.1093/mnras/stad2610
DOI: 10.1093/mnras/stad2610
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