James Webb maps largest cosmic web

On May 17, Live Science drew broad attention to a result that had entered the literature days earlier: astronomers using the James Webb Space Telescope had produced what they describe as the most detailed map yet of the universe’s cosmic web. The underlying study, published in 2026 in *The Astrophysical Journal*, reconstructs the large-scale structure of the universe across roughly 13.7 billion years of cosmic history. The work uses COSMOS-Web, the largest survey carried out with JWST so far, to trace how galaxies cluster into filaments, nodes and voids rather than sitting in space at random. Hossein Hatamnia of the University of California, Riverside, led the study. ### What exactly did the team map? The paper says the team reconstructed the universe’s large-scale structure using 160,000 galaxies with robust photometric redshifts from the COSMOS-Web program. In practice, that means the researchers used galaxy positions and distances to infer the web-like arrangement of denser and emptier regions across cosmic time. The cosmic web is the large-scale framework in which galaxies and galaxy clusters sit along filaments and sheets, with vast voids in between. University statements describing the result said the new map shows those dense filaments and clusters in bright regions and the sparse voids in darker ones, extending back to when the universe was less than 1 billion years old. ### Why was JWST able to do this when earlier telescopes struggled? (iopscience.iop.org) COSMOS-Web was designed as a wide, deep JWST survey, covering a contiguous sky area about the size of three full moons, according to the University of California, Riverside and Phys.org summaries based on the team’s release. That combination matters because earlier maps could identify galaxies individually but blurred the larger architecture they formed together. (phys.org) JWST’s infrared sensitivity let the team detect faint, distant galaxies that were difficult to capture with earlier observatories. Hatamnia said in the university release that “JWST has completely changed our view of the universe,” adding that COSMOS-Web was built to provide the “wide, deep view” needed to see the cosmic web. ### How far back does the map go? The study traces structure up to redshift about 7, which corresponds to a period when the universe was roughly 1 billion years old. (phys.org) The paper says COSMOS-Web reaches 80% mass completeness at about log M*/M☉ ~ 8.7 at z ~ 7, giving the team a way to examine how environment and galaxy growth were linked deep into the early universe. Rochester Institute of Technology, whose faculty were among the co-authors, said the reconstruction follows galaxies across nearly 14 billion years of cosmic history. Jeyhan Kartaltepe, an RIT professor and COSMOS co-leader, said the survey produced “an exquisite three-dimensional view” of the universe from the early period after the Big Bang to today. ### What did the researchers say they learned from the map? (iopscience.iop.org) The paper reports that stellar mass correlates positively with denser environments across all redshifts the team studied. It also says the relationship between star formation and environment changes with time: for quiescent galaxies, star-formation rates decline with density at lower redshift and reverse at higher redshift, while star-forming galaxies show a mild positive correlation up to about redshift 5.5. (rit.edu) The authors wrote that these results show large-scale structure shaping galaxy evolution by boosting early mass assembly in dense regions and later suppressing star formation in lower-mass systems. That interpretation comes directly from the paper’s abstract and from institutional summaries released with the study. ### Is this the same as the recent JWST dark matter map? A separate 2026 paper in *Nature Astronomy* used COSMOS-Web weak-lensing data to produce an ultra-high-resolution map of dark matter over the same field. (arxiv.org) That result traced mass directly through gravitational lensing, while the new *Astrophysical Journal* paper reconstructs the cosmic web from the observed distribution of galaxies and their inferred environments. The COSMOS-Web collaboration has presented the two results as complementary. RIT said the team released both the large-scale structure reconstruction and one of the most detailed high-resolution dark matter maps yet produced from the same survey effort. ### Where does the project go from here? The COSMOS-Web survey completed its observations in May 2024, according to an American Astronomical Society abstract describing the project’s data release timeline. (nature.com) The large-scale structure paper is now part of a broader stream of COSMOS-Web results, with public data products and follow-on analyses continuing to come out through the collaboration and AAS journals. (baas.aas.org) (rit.edu)