Hubble found 22426 globular clusters scattered between the ~1000 galaxies of the coma cluster.
They have been orphaned from their home galaxy due to galaxy near-collisions inside the traffic-jammed galaxy cluster. Because they are so numerous in the Coma cluster, they are excellent tracers of the entire gravitational field...
Hubble revealed that some globular clusters line up along bridge-like patterns. This is telltale evidence for interactions between galaxies where they gravitationally tug on each other like pulling taffy.