Changes of angular momentum and entropy induced by jeans-unstable density waves in stellar disks of flat galaxies

The gravitationally (Jeans-) unstable stellar disks of highly flattened galaxies are considered using a kinetic approach. The model differs from previous work in the inclusion of the terms both with complex conjugates of perturbed equilibrium parameters and with local gradients of equilibrium parameters of the system under study, in addition to the differential rotation and azimuthal gravitational forces. For the first time in galactic dynamics, it is shown that the almost aperiodically growing spiral gravity perturbations (e.g., those produced by a spontaneous perturbation or a satellite system) remove angular momentum from the main domain of the spatially inhomogeneous disk between the inner and outer Lindblad resonances. As a result, the bulk of angular momentum is transferred outward, while the bulk of mass is transported inward. In good conformity with observations, this process leads to the core-dominated exponential-like mass density profile in the disk galaxies, together with the buildup of an extended outer envelope. The coarse-grained entropy of the galactic disk in the main domain is increased by the appearance of density waves, and irreversible phenomena in the stellar system are thereby developed. The latter is a consequence of the nonresonant "heating" of the disk, that is, secular growth of the peculiar kinetic energy and mass redistribution, by growing Jeans-unstable density waves.