Seed fields for galactic dynamos by the magnetorotational instabilities

Abstract

A linear but global numerical model for the magnetorotational instability (MRI) in disk geometry is considered to estimate the instability parameters for galaxies. Similarity rules suggested by a local analysis are applied to reveal a universal behavior approached by the results of global calculations for large magnetic Prandtl numbers. The findings are used to estimate the MRI characteristics for galaxies with their very large magnetic Prandtl numbers which cannot be attained in any numerical simulations. The resulting minimum field for the instability, Bmin 10-25 G, is small compared to any seed fields currently discussed. The growth times of MRI are estimated to be on the order of the rotation period of the inner rigidly-rotating core, i.e. ~100 Myr. Global MRI excites preferentially the magnetic field modes of quadrupolar symmetry.

6 pages, 4 figures, Astron. Astrophys. (acc.)

References in corpus (1)

• Critical Magnetic Prandtl Number for Small-Scale Dynamo

Cited by in corpus (23)

• What is Driving the HI Velocity Dispersion?
• Simulations of magnetic fields in isolated disk galaxies
• Evolution of magnetic fields in galaxies and future observational tests with the Square Kilometre Array
• Magnetised winds in dwarf galaxies
• On the First Generation of Stars
• A three-phase amplification of the cosmic magnetic field in galaxies
• Stability and instability of hydromagnetic Taylor-Couette flows
• Toward a hybrid dynamo model for the Milky Way
• Global Three-Dimensional MHD Simulations of Galactic Gaseous Disks: I. Amplification of Mean Magnetic Fields in Axisymmetric Gravitational Potential
• The influence of the Hall effect on the global stability of cool protostellar disks
• The Weak Field Limit of the Magnetorotational Instability
• Dissipative and nonaxisymmetric standard-MRI in Kepler disks
• Nonlinear Galactic Dynamos and the Magnetic Pitch Angle
• Discussion of the Electromotive Force Terms in the Model of Parker-unstable Galactic Disks with Cosmic Rays and Shear
• The Origin of Magnetic Fields in Galaxies: Observational Tests with the Square Kilometre Array
• The angular momentum transport by standard MRI in quasi-Kepler cylindric Taylor-Couette flows
• Astrophysics in 2005
• Strong turbulence and magnetic coherent structures in the interstellar medium
• Global MRI with Braginskii viscosity in a galactic profile
• Parametric Modulation of Dynamo Waves
• Supernova-driven interstellar turbulence and the galactic dynamo
• Extragalactic magnetism with SOFIA (SALSA Legacy Program) -- IV: Program overview and first results on the polarization fraction
• Supernova origin of galactic turbulence revealed by superbubbles