Astronomer's Accidental Discovery Challenges Models of Early Universe

An accidental discovery by a team of astronomers has upended existing theories about how galaxies formed in the early universe.

The discovery, led by the "Cosmic Web" research group and international collaborators, revealed a disk galaxy with a red glow that is far larger than current models predicted for such an early cosmic time.

The galaxy, now dubbed "Big Wheel," was identified using data from the James Webb Space Telescope (JWST), in an observation campaign that originally had different scientific goals.

The research team, which included astronomers from the University of Milano-Bicocca in Italy and Swinburne University of Technology in Australia, found that this giant disk galaxy existed a mere two billion years after the Big Bang.

"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," Dr. Themiya Nanayakkara, a galaxy spectral modeling expert and a member of the JWST observational team, said in a statement.

The discovery of "Big Wheel" came as a surprise to researchers. The JWST observations were originally targeting a different region of the sky, but the spectral data revealed a previously unnoticed massive disk galaxy, one that was significantly larger than models had anticipated for that time period.

Using data from two of JWST's advanced instruments—the Near-Infrared Camera (NIRCam) and the Near-Infrared Spectrograph (NIRSpec)—the team was able to determine key features of the galaxy, including its redshift, morphology and kinematic structure.

Further spectroscopic analyses confirmed that "Big Wheel" is a disk shape that rotates like a spiral galaxy, similar to our own galaxy, the Milky Way.

"This galaxy, dubbed the 'Big Wheel,' has an optical radius of around 10 kiloparsecs, which is at least three times as large as what is predicted by current cosmological simulations," Nanayakkara said.

The surprising size of "Big Wheel" presents a significant challenge to current astrophysical models, which suggest that large disk galaxies could not have had enough time to form and stabilize so early in the universe's history.

The motion at which "Big Wheel" rotates also confirms that it is not merely a chaotic merger of smaller structures but a fully developed rotating disk—something that was also thought to have been rare in the early universe.

The galaxy appears to reside in a highly over-dense environment, a factor that researchers believe may have been crucial in its unexpected formation. The team speculates that this dense cosmic environment might have created the necessary conditions for such a large disk to take shape much earlier than previously thought.

"Environments of this kind are known to host frequent galaxy encounters, mergers, and gas flows," Nanayakkara explained. "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."

Why This Matters

The discovery challenges the assumption that early galaxies formed primarily through chaotic, disruptive mergers.

Instead, it suggests that certain stable conditions might have been present to allow disk galaxies to grow in a more orderly fashion and maintain their rotational structure.

Finding "Big Wheel" represents a breakthrough in understanding galaxy formation. Until now, astronomers believed that most galaxies from this early period were smaller and irregular in shape.

The discovery now raises new and exciting questions about the processes that shaped the universe's first galaxies.

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Reference

Wang, W., Cantalupo, S., Pensabene, A., et al. (2025). A giant disk galaxy two billion years after the Big Bang. Nature Astronomy. https://doi.org/10.1038/s41550-025-02500-2