COSMOS-Web represents the largest contiguous field surveyed during JWST's first cycle, requiring 270.3 hours of observation time (slightly more than the planned 255 hours due to overhead differences)1. The ambitious program maps a contiguous 0.6 square degrees of sky (roughly the size of three full moons) with NIRCam imaging in four filters (F115W, F150W, F277W, and F444W) and 0.2 square degrees with MIRI in parallel23. Observations were conducted across three main epochs due to JWST's limited viewing windows of the COSMOS field: January 2023, April-May 2023, and December 2023-January 20241.

The survey's exceptional depth and breadth have revealed remarkable details previously invisible to other observatories, including:

• Low-surface-brightness extended halos around massive galaxies4

• Numerous candidate galaxy clusters and protoclusters4

• Gravitational lenses capturing light from distant background objects43

• Complex morphologies of galaxies previously thought to be compact objects3

• Imaging depths reaching 26.7–28.3 AB magnitude (5σ in 0.15" apertures)1

The COSMOS-Web field catalog represents an unprecedented achievement in extragalactic astronomy, documenting nearly 800,000 galaxies across cosmic history. This ambitious undertaking required innovative technological developments and extensive teamwork to process the massive dataset collected by JWST's advanced instruments.1 The catalog is designed for accessibility, with the team releasing not only the raw data but also polished imagery, an interactive viewer, and detailed galaxy parameters to enable further scientific discoveries by astronomers worldwide.21

Unlike previous deep field images like the Hubble Ultra Deep Field (which captured about 10,000 galaxies), the COSMOS-Web field is dramatically larger in scale. As UCSB physics professor Caitlin Casey noted, "If you had a printout of the Hubble Ultra Deep Field on a standard piece of paper, our image would be slightly larger than a 13-foot by 13-foot-wide mural, at the same depth."34 The catalog's comprehensive nature allows astronomers to study not just individual distant galaxies but also their broader cosmic environments, revealing the dense regions and voids that structured the early universe and providing crucial context for understanding galaxy formation and evolution.54

The COSMOS-Web observations are fundamentally challenging our understanding of the early universe. The discovery of massive, well-formed galaxies in the cosmic dawn era contradicts standard cosmological models that predict smaller, less developed structures in the universe's infancy12. One particularly striking example is the identification of galaxies larger than the Milky Way from when the universe was only 800 million years old, which directly conflicts with current formation theories1. Additionally, the clarity of signals from distant galaxies like GS-z13-1 suggests they may originate from the theorized first generation of Population III stars, composed primarily of hydrogen and helium2.

These findings join other mounting challenges to the standard cosmological model, including discrepancies in measurements of the universe's expansion rate when using different methods, inconsistencies in how cosmic structures have clumped together over time, and problems with the universe's apparent uniformity despite insufficient time for light to have traveled between distant regions (the "horizon problem")345. As JWST continues to peer deeper into space, revealing increasingly larger structures that would have had insufficient time to form under current Big Bang timeline constraints, cosmologists are being forced to reconsider fundamental aspects of early universe physics65. These discoveries highlight how advanced observational tools are reshaping our cosmic understanding, pushing theoretical physics into exciting new territory.