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a branch of stellar astronomy that studies the regularities in the motions of stars in the gravitational field of a stellar system and, consequently, the evolution of stellar systems.
The methods of analytic mechanics and statistical physics are combined in stellar dynamics. The means of analytic mechanics alone are insufficient, since the number of stars in stellar systems (excluding multiple stars) is great. Although galaxies contain, in addition to stars, some dust and gas (the motion of which is determined not only by gravitational forces but also by forces of light pressure as well as by forces from the magnetic field of the stellar system), the principal problem of stellar dynamics is the study of the motions of stars, since it is in stars that most of the matter of galaxies is concentrated. The basic types of stellar systems studied in stellar dynamics are galaxies, particularly the Milky Way Galaxy. Globular and open clusters, multiple stars, and clusters of galaxies are also investigated.
An important problem of stellar dynamics in the mid-20th century is the problem of relaxation, which is linked to the investigation of the possible paths that the evolution of stellar systems can take from certain initial states to the state characterized by the stellar velocity distribution observable in the present era. The problem of spiral and ring structures in galaxies occupies an important place in the investigations of stellar dynamics.