An international team has discovered a giant spiral disk galaxy in the early cosmos which is three times larger than similar galaxies of the same epoch.
Galactic disks are flat, rotating structures filled with stars, gas, and dust that orbit the central core. The solar system orbits within the Milky Way’s disk.
Swinburne University of Technology is the only Australian research institution behind this global investigation, published in Nature Astronomy, of the new James Webb Space Telescope (JWST) and other telescope observations.
Swinburne galaxy spectral modeling expert Dr. Themiya Nanayakkara was a part of the international team that planned the JWST observations and discovered this exceptional galaxy.
“When and how galaxy disks form has been an outstanding puzzle,” he says. “Seeing a massive, well-ordered disk galaxy when the universe was just 2.4 billion years old forces us to rethink how rapidly and efficiently nature can build cosmic structures.
“This galaxy not only challenges our existing models of early formation but also hints that dense, gas-rich environments may be the cradle for the universe’s earliest giants.”
These observations were targeted towards a specific region of the sky, which hosts a bright quasar at redshift z=3.25. The galaxy is seen as it was 11 billion years ago, or 2 billion years after the Big Bang.
Using the new JWST data from two onboard instruments, NIRCam and NIRSpec, Dr. Nanayakkara and the team identified galaxies within this over-dense structure and analyzed their redshifts, morphology, and kinematics, all of which are needed for the identification of galaxy disks.
Composite false-color images of the Big Wheel galaxy at z = 3.245. © Nature Astronomy (2025). DOI: 10.1038/s41550-025-02500-2
“Our observations led to the serendipitous discovery of a surprisingly large disk galaxy in our field,” he says. “This galaxy, dubbed the ‘Big Wheel’ has an optical radius of around 10 kpc, which is at least three times as large as what is predicted by current cosmological simulations.”
Further kinematics analysis based on the NIRSpec data confirmed that the galaxy contains a disk rotating at around 300 km/s. It is larger than any other kinematically confirmed disks found at similar early epochs, and yet is comparable to the size of today’s most massive disks.
Dr. Nanayakkara says the disk lives in a highly over-dense environment, hinting that such an environment might have favorable physical conditions for early disk formation.
“Given the lack of comparable galaxies to the Big Wheel in current cosmological simulations, these favorable physical conditions are likely not fully captured yet in current galaxy formation models. Specifically, environments of this kind are known to host frequent galaxy encounters, mergers and gas flows.
“Therefore, in order to have a disk form early and grow quickly, galaxy mergers in this environment must have been non-destructive and oriented in particular directions. Alternatively, gas inflows must have carried angular momentum that largely co-rotated with the galaxy disk.”
Previous studies revealed that the quasar is embedded in a large-scale structure called a proto-galaxy cluster, which has a high concentration of galaxies, gas, and black holes, indicating an exceptionally over-dense environment.
This study paves the way to studying this over-dense environment, which remains a relatively under-explored territory, Dr. Nanayakkara says.
“With more targeted observations, we could build a statistical sample of giant disks in the early universe and open up a new window on the study of early phases of galaxy formation.”
More information:
Weichen Wang et al, A giant disk galaxy two billion years after the Big Bang, Nature Astronomy (2025). DOI: 10.1038/s41550-025-02500-2
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Swinburne University of Technology
Citation:
A ‘surprisingly large’ disk galaxy discovered in the early universe (2025, March 17)
