Gravitational instability in galactic disk: the role of inhomogenities and magnetic field

By means of linear analysis of MHD equations, we study the influence of the global galactic magnetic field on the gravitational instability of a finite thickness gaseous disk. We obtain a dispersion equation for isentropic gaseous disk taking into account both radial and vertical components of the magnetic field, the differential rotation of the gas, and the radial inhomogeneity of the surface density. Combined influence of the magnetic field and the finite gaseous disk thickness suppresses unstable perturbations. In the case of an essentially radially inhomogeneous disk, we predict a complex picture of the interaction of the sound branches of oscillations with gradient oscillations, which has an additional destabilizing effect.