Astronomers at the University of California, Riverside announced on May 11 that they have produced the most detailed map of the cosmic web ever made, using NASA's James Webb Space Telescope to chart 164,000 galaxies across 13.7 billion years of cosmic history — giving physicists, for the first time, a high-resolution observational test bed for competing theories of dark matter and early galaxy formation.
The paper, titled "Large-Scale Structure in COSMOS-Web: Tracing Galaxy Evolution in the Cosmic Web up to z ∼ 7 with the Largest JWST Survey" and published May 6 in The Astrophysical Journal, appeared in the same week the team released its full data catalogue — 164,000 galaxies, a density map, and an animation of the cosmic web evolving over billions of years — to the public, giving researchers worldwide immediate access to the raw material behind the findings.
A Map That Outpaces What Hubble Could See
The map is built on COSMOS-Web, the largest General Observer programme ever approved for JWST. The survey covers a contiguous patch of sky roughly the area of three full Moons and was designed specifically to exploit JWST's infrared instruments, which detect faint, dust-obscured galaxies invisible to visible-light predecessors. Lead author Hossein Hatamnia, a graduate student at UCR and Carnegie Observatories, described the telescope's core advantage: each galaxy can be placed into the correct slice of cosmic time because JWST measures distances with far greater precision than Hubble did, sharpening the map's resolution across every era it covers.
Professor Bahram Mobasher, a distinguished professor of physics and astronomy at UCR and Hatamnia's doctoral supervisor, noted that large-scale structures previously appearing as single objects in Hubble data now resolve into multiple distinct components in the JWST map. A side-by-side comparison shown at a COSMOS collaboration meeting in May 2025 drew spontaneous applause from scientists who had spent careers working with Hubble.
"What used to look like a single structure now resolves into many, and details that were smoothed away before are now clearly visible."
— Prof. Bahram Mobasher, UC Riverside, co-author
What the Cosmic Web Is and Why Its Structure Tests Dark Matter
The cosmic web is the universe's large-scale architecture: a network of dark-matter filaments and gas sheets that encloses vast, nearly empty voids, with galaxies clustering at the densest intersections. It cannot be observed directly because dark matter emits no light; researchers infer its structure from the galaxies that form preferentially along its strands.
Understanding the web is central to two of the deepest unresolved questions in physics: how dark matter is distributed across the universe, and how the first galaxies formed from the void. Theorists have built computer simulations predicting the web's structure for decades, but until now the observational data were too shallow and too coarse to test those models rigorously. The COSMOS-Web map changes that: it reaches back to when the universe was less than one billion years old, an era previously inaccessible to wide-field surveys, and does so at sufficient resolution to distinguish between competing theoretical predictions about filament thickness and cluster mass.
Dark Matter Map Confirms the Filament Network
A complementary study published in Nature Astronomy in January 2026, led by Diana Scognamiglio at NASA's Jet Propulsion Laboratory, used the same JWST dataset to map dark matter through gravitational lensing — the subtle distortion that massive, invisible structures imprint on the shapes of background galaxies. Scognamiglio described the result as seeing the universe's invisible backbone with a new pair of glasses.
"This is the largest dark matter map we've made with Webb, and it's twice as sharp as any dark matter map made by other observatories," Scognamiglio said. The dark matter map aligns tightly with the galaxy filaments detected in the Hatamnia study, providing the most direct visualisation yet of the invisible scaffolding on which visible structure is built.
Galaxy Environment Shapes Mass and Star Formation
The Hatamnia paper also delivers the first statistically robust dataset for studying how a galaxy's position in the web — whether in a void, a filament, or a dense cluster — shapes its evolution over cosmic time. The analysis finds that stellar mass correlates positively with local density at all redshifts examined. For quiescent galaxies, that correlation is strongest at redshifts below 2.5; at higher redshifts, between approximately 2.5 and 5.5, the relationship is confined to extreme overdense environments, consistent with early mass assembly in protoclusters. Researchers are already mining the 164,000-galaxy catalogue for correlations between environment and properties such as star-formation rate and central black hole activity.
Publicly Released Data Opens the Map to Global Research
In keeping with the COSMOS collaboration's tradition of open science, the team has released the full data package publicly — the large-scale structure pipeline, the galaxy catalogue, and the density map — alongside the paper. Mobasher said that also includes a video showing the cosmic web evolving across billions of years. The dataset is expected to anchor galaxy-evolution studies for years, and will serve as a reference against which next-generation cosmological simulations can be tested.
If the simulations and the observed map disagree at sufficient precision, the discrepancy could point toward new physics — or toward revisions in our understanding of how dark matter behaves on the largest scales. Future surveys by ESA's Euclid satellite and NASA's Nancy Grace Roman Space Telescope will apply comparable weak-lensing methods across much larger sky areas, extending the work from a detailed regional study toward a global map of the cosmic web.
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