Astrophysics Suck The Study Of The Accretion Disk

Since about 200 years ago, astrophysicists have studied the accretion disks in the universe, they thought that disks are ubiquitous in astrophysics. Until recently, this deduction was testified by the observations. The study on accretion disks is very important in astrophysics. In this thesis , we will discuss two problems on accretion disks. One is using anomalous viscosity to discuss the stationary vertical structure of a thin disk around a black hole, the other is the wave excitation in a disk by external potential.It is well known that the astrophysical accretion disks are hydrodynamic disks with anomalous viscosity, the viscosity of matter in disks results in a factor of more amplification to the microscopic viscosity. Using the anomalous viscosity (Li &Zhang 2002), we discuss the stationary vertical structure of a thin disk around a black hole. These stationary vertical structures, including distributions of the pressure, temperature, radiative energy flux, mass density and radial velocities are examined. It is shown that the consideration of anomalous viscosity is necessary and the result is well conformed with the α standard prescription. It also proved that the anomalous viscosity is valid.The excitation of waves in disks by an external potential can translate augular momentum. Goldreich and Tremaine in 1979 and Ward in 1986 studied density wave excitation by an external potential in a 2D disk. In this paper, we will study the wave excitation in a 3D disk by external potentials, based on the formalism developed recently by Tanaka, Takeuchi and Ward in 2002. By taking advantage of Fourier-Hermite expansion, a second-order differential equation for a distinct mode is attained. Then, following the standard technique used by Goldreich and Tremaine in 1979, the simplified equations are solved and analytic expressions for the waves excited at various locations and associated augular momentum transfer rate are manifested. It is noted that when we draw it back to 2D conditions, our result is the same as that for the 2D non-self-gravitating case.