Over the past several thousand years, astronomy has seen remarkable progress. Since the 1600s, when simple refracting telescopes were first used to study the sky, technological progress has now enabled astronomers to observe objects billions of light years away. By capturing light that has travelled across the universe for billions of years, scientists can effectively observe the universe’s past and produce images of the early universe. Studying the universe in this dynamic period of its history allows scientists to understand how the universe around us – its stars, galaxies, and abundant astronomical phenomena – came to be.  

The Cosmic Evolution Survey (C.O.S.M.O.S.) collaboration, an international team of over 200 scientists, is at the forefront of efforts to study the early universe. Last month, the team released the C.O.S.M.O.S. 2025 galaxy catalog, a rich collection of many physical parameters of over 700,000 galaxies located in a region of the sky called the C.O.S.M.O.S. field. The catalog was built using 37 multiwavelength images from both ground and space observatories, including the James Webb Space Telescope (JWST), allowing astronomers to study more galaxies and phenomena in this region than ever before. 

Dr. Caitlin Casey, an observational astronomer, has recently joined the physics department at UC Santa Barbara. She co-leads the C.O.S.M.O.S. collaboration — a project distinguished by its deep exploration of the C.O.S.M.O.S. field. This field has proved to be a uniquely rich and largely unobstructed region of the sky, ideal for deep space observation. As Casey explains, “It’s large enough to capture the biggest structures in the universe out to the earliest of times.” The C.O.S.M.O.S. field in particular was chosen due to its precise position away from the centre of our galaxy and the plane of the ecliptic. This enables observatories to take images unpolluted by light sources from our own galaxy. Additionally, its location near the celestial equator means it is visible to both hemispheres, including recent cutting-edge telescopes in Chile. 

The C.O.S.M.O.S. 2025 catalog comes from images collected from observatories across the world, as well as past images taken of the region. The recent addition of JWST data adds unique insight. “We’re able to detect so many galaxies simply because of the remarkable depth of JWST images,” Casey adds. “It is kind of the crown jewel of this new data release.”

JWST’s design enables it to provide sharper deep fields than ever captured before. Its 6.5 meter primary mirror means it can collect far more light than previous telescopes like the Hubble Space Telescope. Just as advantageous is the specific range of wavelengths at which JWST operates, which is key to studies of the early universe. Due to the expansion of the universe, light from these distant young galaxies has been red shifted. These light rays have also lost more energy as they have traversed greater distances in space to reach us. JWST is tuned to detect just the right range of wavelengths such that it is sensitive to light from some of the earliest galaxies ever seen. 

According to Casey, JWST is now revealing the most distant objects that have ever been found — in particular, galaxies that formed when the universe was only 1-2% of its current age. “We’re finally able to see that moment in time because we’re that much more sensitive to infrared wavelengths,” she explains. 

Collecting data from telescopes — which, in its rawest form, is a series of images resulting from several exposures taken over the same region of sky — is only the first of many steps required to draw useful scientific conclusions. 

“We process the image first, and that’s a very detailed process,” Casey explains. “When you take a photo with your phone, the sun may cause some glare or there could be dust on the lens and you would use photoshop to make it look better. We try to do that through a more scientific approach of understanding which pixels are affected by light scattering, masking it and removing it.”

Over the past few years, the C.O.S.M.O.S. collaboration has used supercomputers to process a rich set of images from a variety of observatories’ data on the region. The individual photos were then stitched together to create a large collection that effectively captures the entire cosmos field.

Scientists then apply software to the collection that is capable of identifying and classifying each individual object, as well as determining its brightness and other useful physical parameters. Specifically for galaxies, Casey elaborates, the software identifies “how far away the galaxy is, how massive it is and what its properties are.” 

The results have been compiled by the C.O.S.M.O.S. collaboration into catalogs that are publicly available for scientists around the world to access and analyse. Sharing this largely new and unexplored data has significant benefits, as inviting a large community of researchers increases the chances of spotting anomalies, plotting trends, or making discoveries that could be overlooked by a single team. 

The public is encouraged to explore the data. As Casey explains, “The whole idea of releasing it to the public is that our team is not thinking of every possible way to analyse this data, and we really want to encourage the public to use it broadly.” 

Analysis of this data has already revealed new and interesting results. Directly from the C.O.S.M.O.S.-Web survey data, far more galaxies have been discovered within the first few billion years than expected. Further, these galaxies are brighter and more massive than cosmological models predicted. 

“From studies of the star formation process everywhere else in the cosmos, we know it’s not a particularly efficient process,” Casey explains, “but we see stars too massive to form in such a short period of time, unless the star formation process was much more efficient in these early times.” This surprising result may change scientists’ understanding of galaxy and star formation in the early stages of the universe. 

Scientists are sifting through the C.O.S.M.O.S. 2025 in pursuit of open questions about the universe, such as exploring the detailed substructure of galaxies, how the evolution of galaxies is affected by their surrounding cosmic environment, gravitational lensing and the detection of dark matter in this region of space. 

At UCSB, undergraduate and graduate students in Casey’s lab are also actively engaging with the data set, pursuing projects that range from exploring the distribution of galaxies on a large scale to studying the epoch of reionization — a phase of the early universe that lasted around 1.2 million years — by looking closely at galaxies during this time period specifically. A graduate student in the lab is studying supermassive black holes in the field. “JWST has revealed a really interesting and abundant population of [supermassive black holes] in the early universe … it’s not well understood how supermassive black holes form,” Casey notes. 

One undergraduate researcher, Tomas Forney, is working on probabilistic models to analyse light sources in the field. “What’s exciting is getting to work with data from such a revolutionary tool as the James Webb telescope ” he says, noting that the accessibility of the data makes it possible to apply data analysis techniques as an undergraduate. 

As the C.O.S.M.O.S. collaboration moves forward, its focus remains precise. By devoting attention to a single patch of sky, researchers are able to uncover universal truths about the early universe and galaxy formation at this early time. This deep field survey, now a highly collaborative international effort, continues to shape our understanding of the early universe, the processes that led to the universe we see today, and ultimately our place within it.