Using this method the astronomers were able to study a much larger area of the cluster than in previous studies of distant clusters. The cluster was observed with the 10m W. M. Keck Telescope on Hawaii February 1998 to determine which galaxies are members of the cluster. In most cases we see two galaxies very close together, with distorted morphologies. The distortions in the morphologies are the result of huge tidal forces that are caused by the gravitational interaction of the merging galaxies. Among the distortions seen in the distant mergers are asymmetries, and streams of stars being pulled out of the galaxies.
Galaxies consist largely of dark matter.
When galaxies approach each other they are slowed down by the gravitational pull of the dark matter. Computer simulations show that low velocity encounters of galaxies lead to their merger, thereby forming a new, larger galaxy. Large tidal forces act on the galaxies as a result of the gravitational interaction. These forces can pull streams of stars from the galaxies. Such asymmetric star streams can be seen in some of the mergers observed with the Hubble Space Telescope.