Dynamical evolution in galactic disks

摘要: The dynamical structure of a galactic disk is changed by fluctuations in its gravitational potential field. orbits stars are deflected, changing the velocity dispersion and angular-momentum distribution. We derive an expression for induced changes phase-space distribution function, finding them to be second order perturbing potential, form diffusion phase space. evaluate our result model transient spiral. radial-velocity increases response steady sequence perturbations as t/sup 1/2/, low stars, declining towards 1/5/ radial excursions become large comparison spatial wavelength spirals. waves also transport angular momentum, allowing more centrally concentrated. In equilibrium wave amplitude controlled rate cooling disk, and, inasmuch gas gives rise star formation, heating time scale may similar star-formation scale. Spiral then rearrange out gas. Our predictions good agreement with age/velocity-dispersion relation observed N-body experiments,more » we conclude that recurrent spirals naturally account solar neighborhood stars.« less