2008/06/26 by Kostas Kleidis, K. Kleidis, A. Kuiroukidis +5
Physics and Astronomy · #Anisotropy #Astrophysics #Black Holes and Theoretical Physics #Classical mechanics #Cosmology and Gravitation Theories #Friedmann–Lemaître–Robertson–Walker metric #Gravitation #Gravitational collapse #Instability #Isotropy #Magnetic field #Mechanics #Physics #Quantum mechanics #Solar and Space Plasma Dynamics #Universe #astro-ph
paper · pdf · doi:10.1142/s0217751x0804127x
published as Int.J.Mod.Phys.A23:4467-4484,2008 · 10 pages RevTex, 4 figures, accepted for publication in the International Journal of Modern Physics A
arxiv created 2008/06/26 · openalex publication_date 2008/11/10 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Gravitational instabilities in a magnetized Friedman–Robertson–Walker (FRW) universe, in which the magnetic field was assumed to be too weak to destroy the isotropy of the model, are known and have been studied in the past. Accordingly, it became evident that the external magnetic field disfavors the perturbations' growth, suppressing the corresponding rate by an amount proportional to its strength. However, the spatial isotropy of the FRW universe is not compatible with the presence of large-scale magnetic fields. Therefore, in this paper we use the general-relativistic version of the (linearized) perturbed magnetohydrodynamic equations with and without resistivity, to discuss a generalized Jeans criterion and the potential formation of density condensations within a class of homogeneous and anisotropically expanding, self-gravitating, magnetized fluids in curved space–time. We find that, for a wide variety of anisotropic cosmological models, gravitomagnetic instabilities can lead to subhorizontal, magnetized condensations. In the nonresistive case, the power spectrum of the unstable cosmological perturbations suggests that most of the power is concentrated on large scales (small k), very close to the horizon. On the other hand, in a resistive medium, the critical wave-numbers so obtained, exhibit a delicate dependence on resistivity, resulting in the reduction of the corresponding Jeans lengths to smaller scales (well bellow the horizon) than the nonresistive ones, while increasing the range of cosmological models which admit such an instability.