AbstractThe dynamical instability of motions is studied numerically for the triplets of stars and galaxies. The models of equal-mass components which are in rest initially, are investigated. The divergence of initially near by trajectories close to exponential one is observed in the configurational as well as the phase space. The characteristic time of such divergenee is less for the configurations which are initially hierarchical. The presence of significant dark matter distributed over the whole volume of system speeds up the rate of stochastisation considerably.

The character of the galaxy motions in three observed samples of galaxy triplets-is studied using data on the radial velocities and relative positions of the components in the plane of the sky. These three samples are very different with respect to the compactness of the triplets. We demonstrate an isotropic distribution of the velocities of the components for the 45 triplets from the list of Karachentseva et al. that are probably physically associated, as well as for the 50 triplets-from the Catalogue of Southern Galaxy Groups. For the 40 triplets from the galaxy groups of Huchra & Geller, both isotropic systems and collapsing (or expanding) systems are possible. The isotropic distribution of velocities suggests virialized systems, possibly with large amounts of dark matter.