Anomalous Viscosity Of The Magnetized Accretion Disk Structure And Stability

It is well known that the astrophysical accretion disks are hydrodynamic disks with anomalous viscosity, the viscosity of the matter in disks results in a factor of more than 108 amplification to the microscopic viscosity. The anomalous viscosity has disturbed the astrophysicists for a long time, until recently it is resolved by Li X. . In this thesis, using the new model of anomalous viscosity, we discuss the structure of magnetized thin accretion disks, the magnetic instability in the accretion disks and the effect of the anomalous dissipation on magnetic rotating instability. To investigate these problems, the thesis consists of three chapters.In chapter one. magnetohydrodynamic processes in thin accretion disks involving magnetic viscosity are investigated. These stationary structures, including distributions of the surface mass density, temperature, velocity and magnetic fields of a disk around a young stellar object, are numerically examined. It is shown that the consideration of anomalous viscosity is necessary for the validity of the distribution. For example, the surface density is a decreasing function of radius because of it and there is a strange increasing part in the distribution of the density if it is ignored. In particular the distribution of effective temperature is a smoothlydecreasing function of radius with power index q = -1/2, corresponding to theobserved radiation flux density, provided that the magnetic fields are suitably chosen.In chapter two, using the new model of anomalous viscosity, we investigate the magnetic instability in the accretion disks and give the dispersion formula. On the basis of the dispersion relation obtained, it is numerically shown that the instability condition of viscous accretion disk is well consistent with that of the ideal accretion disk, namely there would be magneto-rotational instability in the presence of avertical weak magnetic field. For a given distance r from the center of the disk, the growth rate in the anomalous case deviates from the ideal case more greatly when the vertical magnetic field is smaller: the large viscosity limits to the instability; In the two cases, the distributions of growth rate with wave number k approach each other when the magnetic field increases: it greatly represses the effect of viscosity.In chapter three, on the basis of the new anomalous magnetic Prandtl number in accretion disks, we study the effect of dissipation on magnetic instability of Keplerian disks. By analyzing numerically the disks around a young stellar object (YSO) and a black hole, we can obtain: the dissipation can not be neglected as a magnetic field is in small threshold value; in Keplerian disks, the magnetic field is smaller, the dissipation caused by anomalous viscosity and anomalous resistivity deviates from the ideal more greatly; the dissipative effects on magnetic instability become smaller as the radius r becomes larger.