... Still, the detailed information available from clusters of galaxies like Abell 1689 gives hope that one day full solutions will be found that will not only fully reveal the dark matter in clusters , but also reveal the amounts of dark energy in the universe needed to lie along the line of sight to the distant arcs . ... Publications with keywords: abell 1689 - galaxy cluster - dark matter . Publications with words: abell 1689 - galaxy cluster - dark matter . ... The Hercules Cluster of Galaxies . ...