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 km/s. 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 km/s toward the Virgo Cluster.