利用反常粘滞研究吸积盘的脉动不稳定性

Study of pulsational instability of accretion disks with anomalous viscosity

从磁流体动力学方程组出发,用微扰法得出含反常粘滞、反常阻抗、环向磁场和垂向磁场的吸积盘的色散方程。在弱磁场情况下,数值计算结果表明盘内区存在1种不稳定的单调模式和3种稳定的单调模式,磁场对单调不稳定性表现为非稳因素。随着磁场的增强,单调模式消失,盘内出现4种轴对称振荡模式,其中两种振荡模式是脉动稳定的,环向磁场对其表现为非稳因素,垂向磁场对其表现为致稳因素;另两种振荡模式在波数比较小时是不稳定的,随着波数的增大,这两种模式也是脉动稳定的,环向磁场和垂向磁场分别对他们表现为致稳因素和非稳因素。

Starting from the equations of magnetohydrodynamics, the dispersion equation of accretion disks including a- nomalous viscosity, anomalous resistivity, azimuthal magnetic field and vertical magnetic field is derived from the pertur- bation method. It is numerically shown that there exist one monotonous mode of instability and three monotonous modes of stability in the inner disk region if the magnetic field is weak, and the magnetic field acts as a factors of instability for the monotonous mode of instability. The monotonous modes diminish and there are four modes of oscillations in the disks when the magnetic fields strengthen. Two of them are always pulsationally stable, and the azimuthal magnetic field acts as a factor of instability, while the vertical magnetic field is the stabilizing factor. The other two modes are in- stable if the wave number is small, and they become stable when the wave number increases. The azimuthal magnetic field and vertical magnetic field act as factors of stability and instability, respectively.