This composite color-image shows the brightest galaxies in four groups located about 4 billion light-years away. The galaxies are ordered in increasing stellar mass. The brightest galaxies in group 1 and 2 both have obvious bright, gravitationally bound companions. The inset in this image obtained with the Hubble Space Telescope shows that the brightest galaxy in group 3 has also a double nucleus. Thus, these galaxies are currently in the process of merging.