JWST reveals largest-ever cosmic megastructure map

Astronomers using the James Webb Space Telescope have produced the most detailed map yet of the cosmic web, the filament-and-void structure that links galaxies across the universe. The result comes from COSMOS-Web, the largest General Observer program selected for Webb, and traces large-scale structure across 13.7 billion years of cosmic history. Researchers led by the University of California, Riverside said the map follows the galaxy network back to when the universe was about 1 billion years old. The work was published in *The Astrophysical Journal*. ### What exactly did Webb map here? The new map reconstructs the cosmic web, the large-scale framework in which galaxies and galaxy clusters sit. In the researchers’ description, that framework consists of dense filaments and sheets surrounding vast, relatively empty voids. Bright regions in the visualization mark denser clusters and filaments, while darker regions show the voids between them. (phys.org) Hossein Hatamnia of UC Riverside, the study’s lead author, said COSMOS-Web was designed to provide the “wide, deep view” needed to see that structure. The survey used Webb’s infrared sensitivity to detect faint, distant galaxies that earlier observatories could not capture as effectively, allowing the team to trace the network farther back in time. (rit.edu) ### Why is COSMOS-Web different from earlier deep-space maps? COSMOS-Web covers a contiguous sky area of about 0.6 square degrees, roughly the size of three full moons, according to the collaboration and the study materials. That scale matters because many earlier flagship deep-field images reached extreme depth over much smaller patches of sky. COSMOS-Web was built to combine depth with width, reducing the risk that a small field would give a distorted view of how matter is distributed. (phys.org) The COSMOS collaboration said in June 2025 that it had publicly released imaging and a catalog of nearly 800,000 galaxies spanning nearly all of cosmic time. The newer large-scale-structure paper uses a subset of that broader field to reconstruct how galaxies trace the web across cosmic history. ### How far back does the map go? (phys.org) The study says the reconstruction reaches up to redshift about 7, corresponding to a universe less than 1 billion years old. In the published visualization, the present day sits at one end of the map, and moving outward places galaxies by cosmic time, extending across nearly 14 billion years. (physics.ucsb.edu) The team applied a weighted kernel density estimation method to roughly 160,000 galaxies with robust photometric redshifts, according to the paper abstract. That let the researchers infer where denser environments and emptier regions sit across different eras of the universe. ### What did the researchers say they found? The paper says stellar mass correlates positively with density at all redshifts examined, meaning denser regions tended to host more massive galaxies. (rit.edu) The authors also reported that environment appears to shape galaxy evolution differently over time: dense regions enhanced early mass assembly, while at later times low-mass galaxies in denser environments showed more suppressed star formation. (iopscience.iop.org) Jeyhan Kartaltepe of Rochester Institute of Technology, a COSMOS co-leader and study co-author, said the data produced “an exquisite three-dimensional view” of the universe from shortly after the Big Bang to today. RIT said the team has also released a high-resolution dark-matter map tied to the same broader effort. ### Where can readers find the data and paper? (iopscience.iop.org) The COSMOS collaboration says COSMOS-Web is a 255-hour Webb treasury program and describes it as containing about a million galaxies across cosmic time. The large-scale-structure paper, titled “Large-Scale Structure in COSMOS-Web: Tracing Galaxy Evolution in the Cosmic Web up to z ∼ 7 with the Largest JWST Survey,” is published in *The Astrophysical Journal*. The collaboration’s COSMOS-Web page lists Kartaltepe and Caitlin Casey as the survey’s principal investigators and hosts project information for the public dataset. (rit.edu) (cosmos.astro.caltech.edu)