The Nature of Small-Scale Perturbation Modes in a Nonstationary Self-Gravitating Disk

In this work, we investigate the nature of gravitational instability of small-scale perturbation modes during the early nonstationary stages of the evolution of disk-like galaxies. To this end, we study the gravitational instability of small-scale horizontal perturbation modes, such as $(m;N)=(12;20)$, $(14;20)$, $(16;20)$, and $(18;20)$, in the framework of a nonlinear nonstationary anisotropic model of a self-gravitating disk. The corresponding nonstationary analogues of the dispersion equation for these perturbation modes are derived, and their numerical analysis is performed. The results are presented in the form of critical dependences of the initial virial ratio on the disk rotation parameter. The nature of the instability of small-scale perturbation modes in a nonlinear nonstationary self-gravitating disk is determined, and a comparative analysis of their instability increments is carried out.