As we've discussed in class, there are deviations from the Hubble flow of galaxies known as peculiar velocities. At late times in the Universe's history these peculiar motions are due purely to gravitaional accelerations from asymmetric mass distributions on relatively small scales. The Local Group of galaxies sits at the edge of what is known as the Local Supercluster (see Figure 3) which is dominated by the Virgo cluster. The Local Group is being gravitationally pulled toward the Virgo cluster, this is called the Virgocentric infall.
Figure 3: The distribution of 2175 bright galaxies, out to roughly 50 Mpc. The Local Supercluster extends to the right, with the Milky Way (at center) located near the edge of the supercluster. The plane of the Milky Way bisects the ``empty'' slices; galaxies within the slices are hidden from view by Galactic dust and gas (the zone of avoidance). (Figure from Tully, Ap. J., 257, 389, 1982.)
What time would we want to use? Write in terms of G, the total mass of the Local Supercluster, M, the distance to the cluster, d, and your expression for time.
where is the cosmological density parameter. After completing Problem #3 of this assignment come back to this part and tell me why this expression kinda makes sense. Use and the previous values for , and distance, and also include your previous expression for g. Calculate the mass of the Local Supercluster (in solar masses) assuming that our motion relative to the cluster is not strongly disturbed by the tidal fields of more distant mass concentrations.