The phrase "massive galaxies" refers to extremely large and heavy collections of stars, planets, and other celestial objects that exist in space. Full definition
In fact, the colors represent dark matter, galaxies and hot gas formed from the collision of massive galaxy clusters. (livescience.com)
Without a significant source of heat, the most massive galaxies in the universe would be forming stars at extreme rates that far exceed observations. (sciencedaily.com)
The discovery could help astronomers understand how the most massive galaxies in the universe are built. (sciencenews.org)