Galactic split provides clue to dark matter mystery
Separation of stars from invisible mass suggests existence of self-interacting particles

GALACTIC SMASH-UP The many galaxies of the cluster Abell 3827 appear in this Hubble Space Telescope photograph. The center of the cluster contains four colliding galaxies (yellow blobs). The bluish circle around the galaxies is the light from a more distant galaxy bending around the cluster’s center due to gravity from both stars and dark matter.
ESO