On the Structure of Advective Accretion Disks at High Luminosity

Global solutions of optically thick advective accretion disks around blackholes are constructed. The solutions are obtained by solving numerically a setof ordinary differential equations corresponding to a steady axisymmetricgeometrically thin disk. We pay special attention to consistently satisfy theregularity conditions at singular points of the equations. For this reason weanalytically expand a solution at the singular point, and use coefficients ofthe expansion in our iterative numerical procedure. We obtain consistenttransonic solutions in a wide range of values of the viscosity parameter alphaand mass acretion rate. We compare two different form of viscosity: one takesthe shear stress to be proportional to the pressure, while the other uses theangular velocity gradient-dependent stress. We find that there are two singular points in solutions corresponding to thepressure-proportional shear stress. The inner singular point locates close tothe last stable orbit around black hole. This point changes its type from asaddle to node depending on values of alpha and accretion rate. The outersingular point locates at larger radius and is always of a saddle-type. Weargue that, contrary to the previous investigations, a nodal-type innersingular point does not introduce multiple solutions. Only one integral curve,which corresponds to the unique global solution, passes simultaneously theinner and outer singular points independently of the type of inner singularpoint. Solutions with the angular velocity gradient-dependent shear stress haveone singular point which is always of a saddle-type and corresponds to theunique global solution. The structure of accretion disks corresponding to bothviscosities are similar.Comment: 20 pages, 6 figures, submitted to Ap