Galactic collisions show where dark matter goes
This new image of super-cluster Abell 2744 captures the wreckage of a collision between four smaller galaxy clusters. New data let astronomers map the positions of three different kinds of matter in the system, which may offer clues to how dark matter behaves when it smacks into ordinary matter.
The cluster, nicknamed “Pandora’s Cluster” for its bizarre complexity, is as massive as 1.8 quadrillion suns and contains trillions of stars. Only about 5 percent of that mass is made up of galaxies that glow in visible light.
The rest of the mass is gas (20 percent, shown here in pink) that’s so hot it’s only observable through the X-rays it emits, and dark matter (75 percent, blue), which is utterly invisible.
To figure out dark matter’s location, astronomers looked for the telltale stretching of galaxies located far behind the cluster. Huge masses warp the shape of space-time in their vicinity and bend the path of light, a phenomenon called gravitational lensing. By carefully plotting how galaxies in the background are distorted, astronomers can map where the invisible mass of dark matter lies.