2008/01/01 by C. Cremaschini, A. Beklemishev, J. Miller +2 · 5 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Curvature #Dust and Plasma Wave Phenomena #Gravitation #Gravitational field #Magnetic field #Magnetohydrodynamics #Neutron star #Plasma #Rotational symmetry #Toroid #Toroidal and poloidal #astro-ph
paper · pdf · doi:10.1063/1.3076440
published in AIP conference proceedings, 1067-1072 (American Institute of Physics)
openalex publication_date 2008/01/01 · arxiv created 2008/06/27 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The consistent theoretical description of gravitational Hall‐MHD (G‐Hall‐MHD) equilibria is of fundamental importance for understanding the phenomenology of accretion disks (AD) around compact objects (black holes, neutron stars, etc.). The very existence of these equilibria is actually suggested by observations, which show evidence of quiescent, and essentially non‐relativistic, AD plasmas close to compact stars, thus indicating that accretion disks may be characterized by slowly varying EM and fluid fields. These (EM) fields, in particular the electric field, may locally be extremely intense, so that AD plasmas are likely to be locally non‐neutral and therefore characterized by the presence of Hall currents. This suggests therefore that such equilibria should be described in the framework of the Hall‐MHD theory. In addition, for the description of equilibria occurring close to compact stars, the effect of space‐time curvature is expected to become significant. Extending previous approaches, holding for non‐rotating plasmas or based on specialized single‐species model equilibria which ignore the effect of space‐time curvature, the purpose of this work is the formulation of a generalized Grad‐Shafranov (GGS) equation suitable for the investigation of G‐Hall‐MHD equilibria in AD’s where non‐relativistic plasmas are present. For this purpose the equilibria are assumed to be generated by a strong axisymmetric stellar magnetic field and by the gravitating plasma characterizing the AD. Basic features of the theoretical model adopted include: the assumptions of finite plasma rotation, two‐species fluid fields, divergence‐free electric current density and (primarily) toroidal plasma current. As a consequence, an equilibrium equation is obtained from Ampere’s law for the poloidal magnetic flux function. In this paper an approximate solution method is proposed for the GGS equation, permitting the systematic construction of approximate analytical solutions near the equatorial plane of the AD.