The Influence Of Viscosity On The Truncation Of Accretion Disk Around Black Holes

In this thesis I briefly introduce the definitions, classification, some observational characteristics of different black hole accretion models. We focus on the disk corona model, and get some new results.The thesis is composed of 3 chapters. Chapter 1 is on the accretion model and observational characteristics. Spherically symmetric accretion, standard thin disk, SLE disk, advection dominated accretion flow(ADAF), Slim disk, and combined models (such as "thin disk + ADAF" , "thin disk + Slim" and "thin disk + SLE") are introduced. We also compare the models. In the spherically symmetric accretion model, the mass is accreted to the accretor directly, and the angular momentum of gas can be negligibly small. In the SSD(standard thin disk) model, the angular momentum of gas cannot be neglected, and the mass flow is accreted via a geometrically thin and optically thick disk. The SLE disk is different from SSD, and has a geometrically thick, gas pressure dominated structure. ADAF and Slim disk are both non-geometrically-thin, non-Kepler-rotated. But ADAF is optical thin, Slim disk is optical thick. We also introduce the relation between spectral states and accretion rate. Spectral states as high state, low state, intermediate state, quiescent state, and very high state are mentioned.Chapter 2 is about the disk-corona model. We show the general feature of the physics of frictionally heated corona. Starting with the five equations of viscous hydrodynamics, we deduced theγ-component of the equation of motion, theρ- component of the equation of motion, the z-component of the equation of motion, mass-conservation, and energy-conservation equations. We also introduce the four ordinary differential equations, the approximation, the structure of corona, the equilibrium between the corona and disk, the coronal structure changing with the distance from the black hole.In chapter 3, We use the disk-corona model (Meyer et al. 2000b) to investigate how the viscosity affects the truncation of disk in black hole binaries and low-luminosity AGN (LLAGN), and high/low state transition in AGN and black hole binaries. Previous studies show that the corona structure may depend strongly on the value of viscosity. Now we give our calculation results of changed viscosity coefficient, For a given black hole mass M = 10⁸M_☉, we calculate the coronal structure for a series of viscous coefficients. By comparing the results with a 10M_☉black hole, we find that they are nearly the same (scaled in Eddington accretion rate and Schwarzchild radius). We give analytical fitted formulae for the relation between the mass evaporation rate and viscosityα: M//M_EDD≈1.080α^3.35; and for the relation between the truncation radius and the viscosity:R/R_s≈36.11α^-194. From the relations we find that, the evaporation rate increases withα, and the radius of the maximal evaporation rate decreases withα. This may explain why the spectral transits in different accretion rate. If the accretion rate is larger than maximum evaporation rate, the disk may extend to the last stable orbit, and the system will be in soft state. If the accretion rate is less than maximum evaporation rate, the mass in the inner zone of the disk will be depleted by evaporation. And the ADAF is dominated. The system will be in hard state. We also apply these results to a few balck hole binaries such as XTE J1118+480, GX 339-4, and AGN, NGC 4636.