Ancient proto-supercluster COSMOS-z3.1-A: a 5,000 Milky Way–mass giant from the early universe

Astronomers using deep imaging and spectroscopy identified COSMOS-z3.1-A as the earliest and most distant protocluster, seen when the Universe was about 2.1 billion years old and containing roughly 5,000 times the Milky Way’s mass. The object is a proto-supercluster that will merge into a giant cluster, with 3D mapping showing dense, clumpy subregions at the intersections of the cosmic web, illustrating bottom-up structure formation. The study, part of the ODIN survey, also highlights COSMOS-z3.1-C as another dense protocluster and anticipates evolving into masses surpassing the Coma Cluster; future surveys like the Vera Rubin Observatory’s LSST will help find more such ancient giants.