infall velocity

The infall velocity is the velocity with which an object falls toward the center of a region of gravitational influence. For example, the infall velocity of an object 1,800 astronomical units (AU) away from a star of one solar mass, in the absence of other factors, is about 0.5 kilometers per second. On a larger scale, galaxies and even clusters of galaxies may be drawn toward enormous concentrations of mass. Our own Local Group has an infall velocity of about 350 kilometers per second toward the Virgo Cluster.