对等温、有磁薄吸积盘脉动不稳定性的多因素影响

Multi-Factor Influences on the Pulsational Instability of Isothermal Thin Accretion Disks with Magnetic Fields

本文从磁流体动力学方程组出发，用微扰法得出等温有磁薄吸积盘径向脉动不稳定性的色散方程，详细讨论了磁场、径向粘滞力和因果性修正的α型粘滞对吸积盘不稳定性的影响．我们的结论是：磁场是一种在全盘区域起作用的非稳因素，它能影响粘滞模式的不稳定性和两种声波模式（O－mode和Ⅰ－mode）的增长率．径向粘滞力是一种在全盘区域起作用的致稳因素，它主要影响两种声波模式的不稳定性．α型粘滞的因果性修正主要在盘内区起作用，它对吸积盘的不稳定性影响较为复杂：对粘滞模式和无磁盘的Ⅰ-mode，它表现为致稳因素，而对O－mode和有磁盘的两种声波模式，则表现为非稳因素．

Starting from MHD, the dispersion equation of the pulsational instability of isothermal thin accretion disks with magnetic fields is derived by using the perturbation method. The multi-factor influences of magnetic fields, radial viscous forces and the causally modified α-viscosity on the instability of the disk are discussed in details. We find that the magnetic field is an unstable factor acting on the whole disk, which affects the instability of viscous modes and the growth rate of the two acoustic modes (O-mode and Ⅰ-mode). Radial viscous force is a stability factor acting on the whole disk, affecting the instability of the two acoustic modes. The causally modified α-viscosity acts mainly on the inner disk and its influences on the instability is complicated: It acts as a stabilizing factor for viscous modes and Ⅰ-mode of disk without magnetic fields, but acts as an unstable factor for O-mode and Ⅰ-mode of the disk with magnetic fields.