New James Webb Space Telescope observations indicate that early galaxies shortly after the Big Bang were more chaotic than previous results suggested.
After reviewing over 250 Webb Telescope observations of early galaxies from 800 million to 1.5 billion years after the Big Bang, University of Cambridge researchers discovered a complex and “messy” pattern of unevenness.
Instead of the smooth rotating disks seen in our modern galaxy, the data revealed lumpy, turbulent systems, as revealed in new research published in Monthly Notices of the Royal Astronomical Society.
A Calming Effect
Over time, galaxies have trended toward order and calm according to the Cambridge researchers. Yet in the beginning, amidst frequent powerful events such as star formations and gravitational instabilities, the resultant turbulence contributed to galactic upheaval.
“We don’t just see a few spectacular outliers – this is the first time we’ve been able to look at an entire population at once,” said lead author Lola Danhaive from Cambridge’s Kavli Institute for Cosmology. “We found huge variation: some galaxies are beginning to settle into ordered rotation, but most are still chaotic, with gas puffed up and moving in all directions.”
Grism Mode
To capture these observations, the team utilized the James Webb Space Telescope’s NIRCam by activating the instrument’s grism mode, a setting rarely used by the space observatory.
When Webb collects data about celestial objects, it not only takes high-resolution pictures but also splits light into its component wavelengths using small optical devices known as grisms, or grating prisms. Operating between 2.4 and 5.0 micrometers, these devices enable Webb to perform slitless spectroscopy, which captures the infrared “fingerprints” of stars, exoplanets, and distant galaxies to reveal their chemical makeup.
The NIRCam’s grisms are designed to capture and separate light with a resolving power of around 1,600, meaning that it is capable of providing highly detailed spectral data. However, there are actually two observing “grism modes” that Webb is capable of. One is designed for wide-field spectroscopy, allowing it to study multiple targets at once, while the other is used for time-series observations that monitor single, bright objects (an example might be a transiting exoplanet).
Initially developed to aid in the alignment of the telescope’s mirrors, the grisms now offer a unique tool that, while rarely used, offers a powerful means of studying the composition of alien worlds and the evolution of galaxies across cosmic time.
In their recent research, the team used the grism mode data they obtained and compared it to existing James Webb Space Telescope images using a new algorithm to measure gas movement within individual galaxies.
“Previous results suggested massive, well-ordered disks forming very early on, which didn’t fit our models,” said co-author Dr Sandro Tacchella from the Kavli Institute and the Cavendish Laboratory. “But by looking at hundreds of galaxies with lower stellar masses instead of just one or two, we see the bigger picture, and it’s much more in line with theory. Early galaxies were more turbulent, less stable, and grew up through frequent mergers and bursts of star formation.”
“This work helps bridge the gap between the epoch of reionisation and the so-called cosmic noon, when star formation peaked,” said Danhaive. “It shows how the building blocks of galaxies gradually transitioned from chaotic clumps into ordered structures, and how galaxies such as the Milky Way formed.”
James Webb Space Telescope Results
The work is another example of how the James Webb Space Telescope allows researchers to peer farther out in space and therefore farther back in time. These observations are allowing scientists to observe the galaxy on an entirely new scale, filling in blank spots in the cosmic timeline and providing the evidence to confirm or refute theories of galactic evolution.
In future research, the team plans to piece together the early universe more fully. Their next steps will be to combine this work with cold gas and dust observations in their quest to understand the aftermath of the Big Bang.
“This is just the beginning,” said Tacchella. “With more data, we’ll be able to track how these turbulent systems grew up and became the graceful spirals we see today.”
The paper, “The Dawn of Disks: Unveiling the Turbulent Ionised Gas Kinematics of the Galaxy Population at 𝑧 ∼ 4 − 6 with JWST/NIRCam Grism Spectroscopy,” appeared in Monthly Notices of the Royal Astronomical Society on October 22, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.