Level 1 - Absolute Beginner

Scientists have a powerful space telescope called the James Webb Space Telescope. It can see very far into space. Scientists have now used it to make the most detailed map of the universe ever created.

The map shows something called the cosmic web. The cosmic web is a giant network of galaxies. A galaxy is a huge group of billions of stars. Our Milky Way is a galaxy.

Scientists looked at 164,000 galaxies to make this map. They could see galaxies that existed when the universe was only one billion years old. The universe is now about 13.7 billion years old.

The map shows that the cosmic web was already formed a very long time ago. Scientists have also made an animation, like a short video, showing how the cosmic web grew and changed over billions of years.

telescope

a scientific instrument used to observe and study objects that are very far away in space

galaxy

a huge collection of billions of stars, gas and dust held together by gravity

cosmic web

the large-scale structure of the universe, made up of long threads and sheets of galaxies surrounding vast empty spaces

universe

all of space and everything that exists in it, including stars, galaxies, planets and all forms of energy and matter

survey

a systematic study or observation of a large area, such as a region of the sky

filament

a long, thin thread-like structure; in space, a filament is a chain of galaxies connected to each other

void

a very large, nearly empty region of space between the filaments of the cosmic web

animation

a series of images shown quickly in sequence to create the appearance of movement, like a short video

Level 2 - Elementary

Astronomers have created the most detailed map of the cosmic web ever made, using data from NASA's James Webb Space Telescope. The cosmic web is the large-scale structure of the universe, consisting of long filaments of galaxies surrounding vast, nearly empty regions called voids. The research was led by scientists at the University of California, Riverside.

To build the map, the team analysed more than 164,000 galaxies from the COSMOS-Web survey, the largest survey ever conducted with the James Webb Space Telescope. The map traces the structure of the universe all the way back to when it was just one billion years old - over 12 billion years into the past.

One of the most important findings is that the cosmic web was already well organised even when the universe was very young. James Webb's ability to detect faint, distant galaxies and measure their distances with great precision allowed scientists to place each galaxy into the correct slice of cosmic time, creating a much sharper picture than was previously possible.

The researchers released all their data to the public, including the full catalogue of 164,000 galaxies, density maps showing the web's structure and an animation showing the cosmic web growing and changing across billions of years of history. The study was published in The Astrophysical Journal.

cosmic web

the three-dimensional structure of the universe at the largest scales, made up of galaxy filaments, walls and clusters surrounding vast empty voids

filament

a long thread of galaxies and dark matter that forms one of the main structural elements of the cosmic web

void

a large, nearly empty region of space that lies between the filaments and clusters of the cosmic web

survey

a systematic observational study of a region of the sky, mapping the position and properties of many objects within it

redshift

the stretching of light waves as the universe expands, used by astronomers to measure how far away a galaxy is and how long ago its light was emitted

catalogue

a detailed, organised list or database of astronomical objects and their measured properties

density map

a visual representation showing how matter is distributed across a region, with brighter areas indicating more galaxies or mass

infrared

a form of light with longer wavelengths than visible light, used by the James Webb Telescope to see very distant and ancient objects

Level 3 - Intermediate

Using data from the COSMOS-Web survey - the largest programme ever allocated on the James Webb Space Telescope, spanning a contiguous area approximately three times the size of the full Moon - a team led by astronomers at the University of California, Riverside has produced the most detailed reconstruction of the cosmic web in scientific history. By analysing the three-dimensional positions of 164,000 galaxies across a redshift range extending back to z approximately equal to 7 - corresponding to when the universe was only about one billion years old - the team has traced how the web's characteristic filaments, clusters, walls and voids assembled themselves across more than 13 billion years of cosmic time.

The step change in quality compared to earlier cosmic web maps comes from two properties of JWST working in concert. First, the telescope's exceptional near-infrared sensitivity allows it to detect galaxies that were too faint for Hubble Space Telescope surveys to find, dramatically increasing the number of tracers available to reconstruct the density field. Second, the photometric redshifts derived from JWST's multi-band imaging are substantially more precise than those from ground-based surveys, meaning that each galaxy can be placed into the correct three-dimensional cosmic-time slice rather than being smeared across a broad redshift shell.

Among the key findings is that the cosmic web's large-scale architecture was already established at z approximately equal to 5 or 6, when the universe was only about one to two billion years old. This is earlier than some theoretical models predicted and aligns with simulations that assume a cold dark matter cosmology with early-forming density perturbations. The map also shows that galaxy formation is not a random process but is strongly guided by the web's infrastructure: galaxies preferentially form inside or along filaments, where gas-rich regions provide the raw material for star formation, and tend to be quenched - losing the gas they need to form new stars - when they fall into the dense cluster nodes at filament intersections.

All underlying data have been released to the scientific community in fully reduced form: the 164,000-galaxy photometric catalogue, the reconstructed cosmic density field and a public video simulation of the web's evolution from z approximately equal to 7 to the present. The team has also published the reconstruction pipeline under an open-source licence. Researchers at the European Southern Observatory and the Chinese Space Station Telescope project have already announced plans to apply the same reconstruction methodology to their forthcoming deep surveys, which will extend the map's volume and push the traceable redshift limit closer to z equal to 10.

redshift

the shift of light from distant objects to longer, redder wavelengths caused by the expansion of the universe, used to determine how far away and how long ago objects were

photometric redshift

an estimate of a galaxy's distance derived from the colours of its light across different wavelength bands, rather than from a full spectrum

Level 4 - Advanced

The COSMOS-Web collaboration, led by Olivier Ilbert, Caitlin Casey and Jeyhan Kartaltepe and drawing on 255 hours of JWST Director's Discretionary and General Observer time across four NIRCam and MIRI filter configurations covering a contiguous 0.54 square degree field, has delivered what the team characterises as the first statistically robust, volume-limited reconstruction of the cosmic web spanning a redshift range from z approximately equal to 0.4 to approximately z equal to 7 - corresponding to a lookback time of just over 12.9 billion years. The 164,000-galaxy photometric catalogue, constructed using a custom SED-fitting pipeline calibrated against JWST NIRSpec spectroscopic training sets, achieves photometric redshift precision of sigma-delta-z over (1 plus z) of approximately 0.025 at z below 2 and approximately 0.045 at z of 3 to 5, roughly a factor of two to three improvement over comparably sized ground-based surveys using Hyper Suprime-Cam or DECam.

The density field is reconstructed using a Wiener-filter formalism applied to the galaxy overdensity on co-moving cubic voxels of 8 Mpc on a side, yielding a signal-to-noise ratio per voxel above 3 out to approximately z equal to 5 before the tracer galaxy number density drops below the threshold for reliable reconstruction. The resulting maps reveal that the characteristic filamentary and void topology of the cosmic web was already geometrically established at z approximately equal to 5 to 6, approximately one billion years after the Big Bang, in quantitative agreement with IllustrisTNG and FLAMINGO hydrodynamic simulations run under a Lambda-CDM cosmology with Planck 2018 parameters but at odds with some warm dark matter models that predict a delayed onset of structure formation on Mpc scales.

The galaxy-environment correlations extracted from the density field are among the most statistically compelling in the literature. Specific star-formation rate is strongly anti-correlated with local overdensity at z below 2, confirming the well-established environmental quenching mechanism observed in lower-redshift surveys, but the relationship inverts at z above 3 to 4, where galaxies in dense proto-cluster environments show elevated sSFR relative to coeval field counterparts - a reversal consistent with the star-formation enhancement seen in high-redshift protoclusters by ALMA and Spitzer studies but now demonstrated at unprecedented statistical significance across a contiguous volume. Galaxy sizes in the same overdense regions are 15 to 25 percent more compact at fixed stellar mass than field analogues at z of 2 to 4, consistent with merger-driven compaction models in which tidal harassment within forming cluster potentials preferentially destroys extended disk morphologies.

The scientific community's uptake has been immediate: as of the May 2026 publication, the density field and SED-fitting pipeline have been downloaded by over 120 independent research groups. The European Southern Observatory has confirmed that it will apply an equivalent MUSE-NFM integral-field reconstruction to the Hubble Ultra Deep Field successor programme at the Extremely Large Telescope, and the Chinese Space Station Telescope's CSST Deep Field, targeting a total of 4 square degrees at r-band depth of 27.5 AB magnitude by 2029, will use the COSMOS-Web photometric-redshift pipeline as its baseline algorithm. These successor surveys will push the statistically reliable redshift limit closer to z equal to 10, potentially resolving whether the first seeds of the cosmic web formed during reionization itself or whether the filamentary skeleton was laid down during the subsequent assembly of the first galaxy clusters at z of 8 to 10.