Galactic Time Machine: NASA’s Webb Reveals 12 Billion Years of Galaxy Evolution

A sweeping cosmic census from the James Webb Space Telescope has unveiled nearly 1,700 galaxy groups—marking the deepest and largest survey of its kind.

Peering back 12 billion years, this research opens a window into the chaotic youth of the universe, revealing how galaxies evolved from irregular, star-forming structures to the majestic spirals and ellipticals we see today. These galaxy “families” merge, interact, and grow in complexity, influenced by dark matter and colossal black holes. Scientists are now tracing their growth across eons to understand how the universe’s grand architecture came to be.

Time Travel Through the Cosmos

An international team of astronomers has made a groundbreaking discovery using the James Webb Space Telescope (JWST): the largest sample of galaxy groups ever detected. This new cosmic catalog, compiled from a region of the sky known as COSMOS-Web, offers an exciting and detailed look into how galaxies form, grow, and cluster across the vast history of the universe.

These new observations take us on a journey through time, revealing galaxies as they appeared between 12 billion and 1 billion years ago. The study, published on May 19 in Astronomy and Astrophysics, includes nearly 1,700 galaxy groups. One striking image (see image at top of page) from the research, featuring a galaxy cluster over 6 billion light years away, was recently selected as the European Space Agency’s “Picture of the Month.”

Record-Breaking Discovery of Proto-Clusters

“We’re able to actually observe some of the first galaxies formed in the universe,” says Ghassem Gozaliasl of Aalto University, and head of the galaxy groups detection team who led the study. “We detected 1,678 galaxy groups or proto-clusters – the largest and deepest sample of galaxy groups ever detected – with the James Webb Space Telescope. With this sample, we can study the evolution of galaxies in groups over the past 12 billion years of cosmic time.”

The James Webb Space Telescope, which began operations in 2022, is the most powerful space telescope ever built. Its remarkable resolution and sensitivity let scientists observe the faintest galaxies ever recorded—some of them a billion times dimmer than what the human eye can see. And because light takes time to travel across space, these distant galaxies offer a direct look into the early universe, showing us how galaxies looked and behaved billions of years ago.

Dark Matter, Black Holes, and Galactic Evolution

Galaxy groups and clusters are rich environments filled with dark matter, hot gas, and massive central galaxies that often host supermassive black holes, explains Gozaliasl. “The complex interactions between these components play a crucial role in shaping the life cycles of galaxies and driving the evolution of the groups and clusters themselves. By uncovering a more complete history of these cosmic structures, we can better understand how these processes have influenced the formation and growth of both massive galaxies and the largest structures in the universe.”

Galaxies aren’t scattered evenly throughout the universe. Instead, they cluster in dense regions connected by filaments and walls, forming a vast structure known as the cosmic web. Truly isolated galaxies are rare — most reside in galaxy groups, which typically contain anywhere from three to a few dozen galaxies, or in larger galaxy clusters, which can include hundreds or even thousands of galaxies bound together by gravity. Our own Milky Way is part of a small galaxy group known as the Local Group, which includes the Andromeda Galaxy and dozens of smaller galaxies.

Galactic Families and Their Transformations

“Like humans, galaxies come together and make families,” explains Gozaliasl. “Groups and clusters are really important, because within them galaxies can interact and merge together, resulting in the transformation of galaxy structure and morphology. Studying these environments also helps us understand the role of dark matter, feedback from supermassive black holes, and the thermal history of the hot gas that fills the space between galaxies.”

Because the new catalog includes observations that span from one billion to twelve billion years ago, scientists can compare some of the earliest structures in the universe with relatively modern ones to learn more about galaxy groups and how they evolve. Studying the history of galaxy groups can also help astronomers understand how the giant, brightest group galaxies (BGGs) at their centres form through repeated mergers — an area explored in depth across several of Gozaliasl’s recent publications.

From Chaotic Beginnings to Galactic Order

“When we look very deep into the universe, the galaxies have more irregular shapes and are forming many stars. Closer to our time, star formation is what we refer to as ‘quenched’ – the galaxies have more symmetric structures, like elliptical or spiral galaxies. It’s really exciting to see the shapes changing over cosmic time. We can start to address so many questions about what happened in the universe and how galaxies evolved,” says Gozaliasl.

Reference: “The COSMOS-Web deep galaxy group catalog up to z = 3.7” by Greta Toni, Ghassem Gozaliasl, Matteo Maturi, Lauro Moscardini, Alexis Finoguenov, Gianluca Castignani, Fabrizio Gentile, Kaija Virolainen, Caitlin M. Casey, Jeyhan S. Kartaltepe, Hollis B. Akins, Natalie Allen, Rafael C. Arango-Toro, Arif Babul, Malte Brinch, Nicole E. Drakos, Andreas L. Faisst, Maximilien Franco, Richard E. Griffiths, Santosh Harish, Günther Hasinger, Olivier Ilbert, Shuowen Jin, Ali Ahmad Khostovan, Anton M. Koekemoer, Maarit Korpi-Lagg, Rebecca L. Larson, Jitrapon Lertprasertpong, Daizhong Liu, Georgios Magdis, Richard Massey, Henry Joy McCracken, Jed McKinney, Louise Paquereau, Jason Rhodes, Brant E. Robertson, Mark Sargent, Marko Shuntov, Masayuki Tanaka, Sina Taamoli, Elmo Tempel, Sune Toft, Eleni Vardoulaki and Lilan Yang, 19 May 2025, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202553759

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