However, the universe did not evolve out of one even fog. Rather, the universe assembled along an unseen scaffold. Recent observations made using the recently launched James Webb Space Telescope are now revealing this scaffold throughout most of the history of the cosmos.
In a paper in the Monthly Notices of the Royal Astronomical Society, a team from the University of California, Riverside created a map tracing the development of the cosmic web during 13.7 billion years based on the newly released data from the COSMOS-Web survey. The dataset features the locations of 164,000 galaxies as well as density maps that allow other astronomers to observe changes in the structure of the cosmic web through cosmic history. The survey has a field of view about the size of three full Moons, allowing the team to map both dense galaxy clusters and vast voids between them.
While the term may sound unfamiliar, the cosmic web is simply the largest structure in the universe: strings and walls of matter surrounding enormous underdense areas. This means that galaxies are not distributed randomly. Rather, ordinary matter forms structures according to dark matter’s gravitational layout. As such, more precise maps do more than look nicer; they reveal how galaxies form, how they cluster, and how the environment around them evolves.
“JWST has completely changed our view of the universe, and COSMOS-Web was designed from the start to give us the wide, deep view we need to see the cosmic web,” explained Hossein Hatamnia, the lead author of the study. “For the first time we can study the evolution of galaxies in cluster and filamentary structures across cosmic time, all the way from when the universe was a billion years old up to the nearby universe, from when the universe was a billion years old to today.”
The improvement compared to earlier observations made using the Hubble Space Telescope goes beyond incremental. For starters, the sensitivity of Webb’s infrared sensors allowed it to find dimmer galaxies not spotted by older observatories, while its ability to measure distances sorted these galaxies into much cleaner timelines. Furthermore, Bahram Mobasher, the co-author of the study, highlighted how a single feature visible in older images separated into several separate structures thanks to Webb’s higher-resolution imaging capabilities. In another recent research project conducted using JWST, dark matter and normal matter were found to overlap on larger scales, further supporting the hypothesis that galaxies follow an unseen structure.
In fact, it has now become possible to witness the cosmic web at unexpectedly early times. First of all, Webb observed an ancient ten-galaxy string located only 830 million years after the Big Bang with one end anchored to a quasar. Similarly, in another study of early cosmic structures, a 1,050,000 light-year-long filament stretching back 11.7 billion years was identified. These discoveries show how, as part of the cosmic web, filaments acted as highways through which ordinary matter flowed, allowing galaxies to grow.
“The jump in depth and resolution is truly significant, and we can now see the cosmic web at a time when the universe was only a few hundred million years old, an era that was essentially out of reach before JWST,” said Mobasher. What makes this map so important beyond its technical characteristics is the fact that this study made its entire dataset publicly available. By doing so, the team created an open-source resource that will help future astronomers to study the development of galaxies and their evolution.