Astronomers from the University of Cambridge have used the James Webb Space Telescope (JWST) to study the structure and movement of over 250 young galaxies that formed between 800 million and 1.5 billion years after the Big Bang. Their analysis reveals that these early galaxies were significantly more chaotic than those observed in the present universe.
The research team, led by Lola Danhaive from Cambridge’s Kavli Institute for Cosmology, observed that most of these ancient galaxies were turbulent and ‘clumpy’, lacking the smooth rotating disks seen in mature galaxies like the Milky Way. “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 Danhaive. “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.”
The findings, published in the Monthly Notices of the Royal Astronomical Society, indicate that as the universe evolved, galaxies gradually became more stable and orderly. However, during their early stages, intense star formation and gravitational instabilities caused significant turbulence within these systems.
Danhaive developed new software to analyze data collected using JWST’s NIRCam instrument in ‘grism mode’, which detects faint light from ionized hydrogen gas in distant galaxies. By combining this data with images from other JWST surveys, the team measured gas movement within each galaxy.
“Previous results suggested massive, well-ordered disks forming very early on, which didn’t fit our models,” said Dr Sandro Tacchella from the Kavli Institute and 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.”
Danhaive added: “This work helps bridge the gap between the epoch of reionisation and the so-called cosmic noon, when star formation peaked. 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.”
The study demonstrates JWST’s ability to examine galaxy dynamics at a scale previously unattainable. Future research will seek to integrate these findings with data on cold gas and dust for a more complete understanding of early galaxy development.
“This is just the beginning,” Tacchella said. “With more data, we’ll be able to track how these turbulent systems grew up and became the graceful spirals we see today.”
The project received support from organizations including the Royal Society, European Union, and Science and Technology Facilities Council (STFC). The JWST is a collaboration between NASA, ESA, and the Canadian Space Agency (CSA). Data for this research was gathered as part of the JWST Advanced Deep Extragalactic Survey (JADES). Sandro Tacchella is a Fellow at St Edmund’s College, Cambridge; Lola Danhaive is pursuing her PhD in Data Intensive Science at Cambridge.
Reference:
A. Lola Danhaive et al. ‘The dawn of disks: unveiling the turbulent ionised gas kinematics of the galaxy population at z 4-6 with JWST/NIRCam grism spectroscopy.’ Monthly Notices of the Royal Astronomical Society (2025). DOI: 10.1093/mnras/staf1540