Observers investigate a nearby galaxy cluster merger - Observations confirm that early-universe quasar neighborhoods are densely populated with companion galaxies - Dark matter ghosts its way through powerful (and messy) collision of galaxy clusters - Galaxy clusters could be used as dark matter colliders to understand nature of invisible particles, say scientists - Researchers explore an old galactic open cluster - Hubble peers at pair of closely interacting galaxies - Nasa's latest image shows galaxies in 'cosmic interaction' - Daily Telescope: A shiny cluster of stars in a nearby galaxy - Exploring galaxy groups and clusters and their brightest galaxies within the cosmic web - Huge set of galaxies is set to form largest cluster in known universe