NONLINEAR DYNAMICS OF THE LARGE-SCALE STRUCTURE IN THE UNIVERSE

This paper briefly reviews the nonlinear gravitational dynamics in an expanding universe. The gravitational instability is believed to play a key role in the formation of the large-scale structure of the univer se, amplifying primordial small-amplitude random density fluctuations of Gaussian type and then, at the nonlinear stage, transforming them i nto thin dense pancakes, filaments, and compact clumps of matter. Alth ough there are evidences that the distribution of galaxies and the dis tribution of the underlying mass density are not quite the same, it is widely accepted that they become similar when smoothed with a window of a sufficiently large size. At present the formation of galaxies the mselves is very poorly understood and is not discussed here. We discus s scales in the range roughly from 1 Mpc to 100 Mpc (approximate to 3 x 10(24) - 3 X 10(26) Cm). The lower limit is at least 50 times greate r than the size of the luminous part of a large galaxy, and the upper limit is at least 30 times smaller than the size of the observed unive rse. The problem of the formation of the large-scale structure is one of the key problems in modern cosmology and has too many aspects to me ntion in a short paper. Instead I review only the nonlinear evolution of density inhomogeneities on scales in question, which occured relati vely recently. The paper discusses mainly analytical and semianalytica l methods used in examining the nonlinear gravitational dynamics of th e large-scale structure, though many hints were found in N-body simula tions which have played a very important role in confronting theoretic al models with observations.