Some dynamical effects of the cosmological constant

Newton's law gets modified in the presence of a cosmological constant by a small repulsive term (antigravity) that is proportional to the distance. As suming a value of the cosmological constant consistent with the recent SnIa data (Lambda similar or equal to 10(-52) m(-2)), we investigate the signif icance of this term on various astrophysical scales. We find that on galact ic scales or smaller (less than a few tens of kpc), the dynamical effects o f the vacuum energy are negligible by several orders of magnitude. On scale s of 1 Mpc or larger however we find that the vacuum energy can significant ly affect the dynamics. For example we show that the velocity data in the l ocal group of galaxies correspond to galactic masses increased by 35% in th e presence of vacuum energy. The effect is even more important on larger lo w density systems like clusters of galaxies or superclusters.