It's Complicated: Revising Dark Matter's Relationship with Galaxy Groups

Galaxy clusters, containing thousands of individual galaxies, are some of the largest celestial objects in the heavens. In a new study, scientists show that the relationship between galaxy clusters and dark matter — the mysterious stuff that accounts for 80% of the mass in the universe — is more complex than previously thought. Dark matter exerts a gravitational force that prevents galaxies in these clusters from flying off into space, holding the clusters together.