Static configurations and nonlinear waves in rotating nonuniform self-gravitating fluids

Abstract

The equilibrium states and low-frequency waves in rotating nonuniform self-gravitating fluids are studied. The effect of a central object is included. Two-dimensional static configurations accounting for self-gravity, external gravity, and nonuniform rotation are considered for three models connecting the pressure with the mass density: thermodynamic equilibrium, polytropic pressure, and constant mass density. Explicit analytical solutions for equilibrium have been found in some cases. The low-frequency waves arising due to the vertical and horizontal fluid inhomogeneities are considered in the linear and nonlinear regimes. The relationship between the background pressure and mass density is supposed to be arbitrary in the wave analysis. It is shown that the waves considered can be unstable in the cases of polytropic pressure and constant mass density. The additional nonlinear term proportional to the product of the pressure and mass density perturbations, which is usually omitted, is kept in our nonlinear equations. There have been found conditions for this term to be important. Stationary nonlinear wave equations having solutions in the form of coherent vortex structures are obtained in a general form. The importance of involving real static configurations in the consideration of wave perturbations is emphasized.