JWST maps cosmic web across 14 billion years

NASA’s James Webb Space Telescope has given astronomers their clearest wide-field view yet of the universe’s large-scale structure, using the COSMOS-Web survey to trace the “cosmic web” across 13.7 billion years of history. Researchers led by the University of California, Riverside said the map follows the distribution of galaxies back to when the universe was less than 1 billion years old. The work draws on COSMOS-Web, the largest JWST survey, which was designed to image a broad patch of sky rather than the narrow “deep field” views more commonly associated with the telescope. The results were described in a paper posted in November 2025 and highlighted in institutional releases in May 2026. ### What exactly did Webb map? The May 2026 releases describe a reconstruction of the cosmic web — the network of dense filaments, sheets, clusters and comparatively empty voids that shapes how galaxies are distributed through space. In the new map, galaxies are placed by distance and cosmic time, creating a three-dimensional view of structure growth from the early universe to the present day. (phys.org) Hossein Hatamnia, a graduate student at UC Riverside and lead author of the study, said COSMOS-Web was built to provide the “wide, deep view” needed to see that structure. The paper says the team used a weighted kernel density estimation method to reconstruct large-scale structure from galaxies with robust photometric redshifts. ### Why was COSMOS-Web able to do this when earlier surveys struggled? (phys.org) COSMOS-Web covers about 0.6 square degrees with JWST’s Near Infrared Camera and about 0.2 square degrees with the Mid-Infrared Instrument in parallel, according to the survey’s official project pages. NASA said when the program was announced that the area is roughly equivalent to three full moons, making it unusually broad for Webb. (phys.org) Caitlin Casey, a co-leader of the program, said in NASA’s 2021 description that the large area lets researchers look for large-scale structures at the dawn of galaxy formation and map dark matter distributions at very early times. The COSMOS-Web team says the survey will contain about a million galaxies across cosmic time, building on the long-running COSMOS field’s multiwavelength data. (cosmos.astro.caltech.edu) ### How far back does the new map reach? The UC Riverside release said the reconstruction traces the network of galaxies “all the way back” to when the universe was 1 billion years old. The paper frames that reach as extending to redshift about 7, which corresponds to the epoch when the universe was still in its first billion years. The arXiv version of the study says the analysis used 160,000 galaxies with robust photometric redshifts. (science.nasa.gov) The same abstract says COSMOS-Web reaches 80% mass completeness at about log(M*/M⊙) 8.7 at redshift 7, which the authors say enables a view of how environment shaped galaxy evolution from reionization to today. ### What did the researchers say they found inside the web? The paper reports that stellar mass correlates positively with environmental density across all redshifts studied. (phys.org) It says that relation is stronger for quiescent galaxies at redshifts below about 2.5, while at higher redshifts the trend is concentrated in extreme overdense regions consistent with early proto-cluster assembly. The authors also reported that star-formation trends vary with environment and epoch. (arxiv.org) In the abstract, they said quiescent galaxies show a negative relation between star-formation rate and density below redshift about 1.2, with that behavior reversing above about 1.8, while star-forming galaxies show a mild positive correlation up to redshift about 5.5. ### Is this a map of dark matter itself? The cosmic web is understood as a structure shaped by dark matter and gas, but the new result is primarily a galaxy-based reconstruction of large-scale structure rather than a direct image of dark matter. (arxiv.org) The COSMOS collaboration has separately released a JWST-based dark matter map of the same field, using gravitational lensing across a 0.54-square-degree region in Sextans. The COSMOS project said in February 2026 that dark matter in that map was inferred from how unseen mass bends light from distant galaxies. That release described dense clumps and filamentary links overlapping with ordinary matter in the same survey field. ### Where can readers see the data next? The COSMOS project says COSMOS-Web data are publicly available, and the team has posted an interactive DR1 viewer that lets users inspect released NIRCam and MIRI images, catalogs and spectroscopic redshift overlays. (phys.org) The survey’s official pages list Jeyhan Kartaltepe and Caitlin Casey as principal contacts for the program. (cosmos2025.iap.fr) (cosmos.astro.caltech.edu)