2.25 billion light years away lies Galaxy Cluster Abell 1689, a region of the universe thick with dark matter. Each dot and swirl you see in this image is not a star, but a galaxy, 100 billion stars each.
What is so special about this far away cluster is the amount of globular clusters surrounding these galaxies. Globular clusters are old stars that orbit outside the main region of a galaxy and are thought to be leftovers from galaxy formation. The Milky Way is thought to have about 150 of these regions, but Abell is thought to have 160,000. Why is a good question and it seems to be linked to dark matter. According to NASA:
"The research team found that the globular clusters are intimately intertwined with dark matter. "In our study of Abell 1689, we show how the relationship between globular clusters and dark matter depends on the distance from the galaxy cluster's center," explained team member Karla Alamo-Martinez of the Center for Radio Astronomy and Astrophysics of the National Autonomous University of Mexico in Morelia. "In other words, if you know how many globular clusters are within a certain distance, we can give you an estimate of the amount of dark matter."
From Hubblesite and io9