Relaxation and stability of the disk of our Galaxy

Abstract

From the observed random velocities of 269 stars of spectral type F the relation for the increase of the velocity dispersion upon age σ∼tα is obtained. Both the value α=0.2–0.3 for star’s velocities in the plane of our Galaxy and the value α=0.4–0.6 in vertical direction are determined.Oscillations and stability of stellar‐giant molecular clouds disk of the Galaxy with account taken on binary collisions are considered. Kinetic equation with a model Bhatnagar‐Gross‐Krook collisional integral and the Poisson equation are the basis for our investigation. A dispersion relation is derived to describe the dynamics of small perturbations in the plane of a differentially rotating disk. It is shown: In parts of a colliding two‐component system that are at the boundary of gravitational stability (Jeans’ stability) a specific dissipative instability may grow. As a result, this dissipative instability can increase the dispersion of the random velocities of stars, as the observations have shown.