A model for quasi-spherical magnetized accretion flow

Abstract

Abstract.A model for axisymmetric magnetized accretion flow is proposed. The dominant mechanism of energy dissipation is assumed to be the magnetic diffusivity due to turbulence in the accretion flow. In analogy to the advection-dominated accretion flow (ADAF) solutions, a constant fraction of the resistively dissipated energy is stored in the accreting gas and the rest is radiated. We first introduce the general self-similar solutions which describe a resistive and nonrotating flow with purely poloidal magnetic field. The radial dependence of physical quantities is identical to that in viscous ADAF solutions. Although the main focus of this study is on nonrotating magnetized accretion flow, for rotating flow with both poloidal and toroidal components of magnetic field we find a radial scaling of solutions similar to the nonrotating case. We show that the accretion and the rotation velocities are both below the Keplerian rate, irrespective of the amount of cooling. We show that the set of equations is reduced to one second order differential equation for a nonrotating flow. The geometrical shape of the disk changes depending on the fraction of the resistively dissipated energy which is stored in the accreting gas. However, there is a hot low-density gas above the disk in almost all cases. The net accretion rate is calculated for a set of illustrative parameters.

Self-Similar Solutions for Viscous and Resistive Advection Dominated Accretion Flows

“…Consequently, the role of the magnetic fields on ADAFs has been analyzed in detail by a number of investigators (Bisnovatyi-kogan & Lovelace 2001;Akizuki & Fukue 2006, hereafter AF06;Shadmehri 2004, hereafter Sh04; Ghanbari et al, 2007;Bu, Yung, & Xie 2009;Khesali & Faghei 2009, hereafter KF09). The existence of the toroidal magnetic field has been proven in the outer regions of the discs of young stellar objects (YSOs; Aitken et al 1993;Wright et al 1993) and in the Galactic center Chuss et al 2003).…”

Self-similar structure of magnetized advection-dominated accretion flows and convection-dominated accretion flows

“…The effects of a magnetic field on the disc were also studied (see Balbus & Hawley 1998; Kaburaki 2000; Shadmehri 2004; Meier 2005; Shadmehri & Khajenabi 2005, hereafter SK0; Akizuki & Fukue 2006; Shadmehri & Khajenabi 2006, hereafter SK06; Ghanbari, Salehi & Abbassi 2007). Balbus & Hawley (1998) discussed the MHD turbulence initiated by magnetorotational instability (MRI) and its effects on the angular momentum transportation.…”

A Class of Self‐Gravitating, Magnetized Accretion Disks

“…We assume that the magnitude of is comparable to that of the turbulent viscosity (e.g., Bisnovatyi-Kogan & Ruzmaikin 1976;Shadmehri 2004). Exactly in analogy to the prescription for , we are using a similar form for the magnetic diffusivity ,…”

“…However, these studies neglected the possible effects of magnetic fields. Many authors tried to construct models for a magnetized disk either in a phenomenological way based on some physical considerations (e.g., Shvartsman 1971;Lovelace et al 1994;Kaburaki 2000;Shadmehri 2004;Shadmehri & Khajenabi 2005) (2000) suggested that recent papers discussing advection-dominated accretion flow (ADAF) as a possible solution for astrophysical accretion should be treated with caution, particularly because of our ignorance surrounding the magnetic field. Models of magnetized accretion disks with externally imposed large-scale vertical magnetic field and anomalous magnetic field due to enhanced turbulent diffusion have also been studied (see, e.g., Campbell 2000;Ogilvie & Livio 2001).…”