Vorticity production and survival in viscous and magnetized cosmologies

Abstract

We study the role of viscosity and the effects of a magnetic field on a rotating, self-gravitating fluid, using Newtonian theory and adopting the ideal magnetohydrodynamic approximation. Our results confirm that viscosity can generate vorticity in inhomogeneous environments, while the magnetic tension can produce vorticity even in the absence of fluid pressure and density gradients. Linearizing our equations around an Einstein-de Sitter cosmology, we find that viscosity adds to the diluting effect of the universal expansion. Typically, however, the dissipative viscous effects are confined to relatively small scales. We also identify the characteristic length bellow which the viscous dissipation is strong and beyond which viscosity is essentially negligible. In contrast, magnetism seems to favor cosmic rotation. The magnetic presence is found to slow down the standard decay-rate of linear vortices, thus leading to universes with more residual rotation than generally anticipated.

Minor changes. References added and updated. Published version

References in corpus (6)

• Mach Number Dependence of Turbulent Magnetic Field Amplification: Solenoidal versus Compressive Flows
• Turbulence from localized random expansion waves
• Cosmological magnetic fields from nonlinear effects
• Vorticity production through rotation, shear and baroclinicity
• Can cosmological perturbations produce early universe vorticity?
• Newtonian nonlinear hydrodynamics and magnetohydrodynamics

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