Large spiral galaxies, like the Milky Way, were thought to take billions of years to form. In the Universe’s first billion years, galaxies were expected to be small and chaotic. However, the James Webb Space Telescope (JWST) shows a different story.
Its deep infrared images reveal surprisingly large and well-formed galaxies much earlier than expected, causing astronomers to rethink how and when they formed in the early Universe.
Using data from the James Webb Space Telescope (JWST), an international team led by the University of Geneva (UNIGE) has discovered a massive, Milky Way-like spiral galaxy—Zhúlóng —that formed just 1 billion years after the Big Bang.
Besides being an ultra-massive system, this spiral galaxy, seen at a redshift of 5.2, has a remarkably mature structure, a central old bulge, a large star-forming disk, and well-defined spiral arms.
Zhúlóng means ‘Torch Dragon’ in Chinese mythology. In the myth, Zhúlóng is a mighty red solar dragon who controls day and night by opening and closing its eyes. Each time its eyes open, light floods the world, creating day, and when they close, darkness falls, bringing night. This symbolizes the flow of light and the passage of cosmic time.
The galaxy stands out because it resembles the Milky Way in shape, size, and stellar mass. Its disk is over 60,000 light-years wide, similar to ours, and contains more than 100 billion solar masses of stars.
This makes it one of the best examples of a Milky Way-like galaxy found so early in the Universe, raising new questions about how such large, well-formed spiral galaxies could have formed so soon after the Big Bang.
This discovery highlights how the JWST changes our understanding of the early Universe. Future observations from JWST and the Atacama Large Millimeter Array (ALMA) will help confirm the galaxy’s properties and reveal more about its formation.
As new wide-area surveys by JWST continue, astronomers expect to find more galaxies like this, providing fresh insights into the complex processes that shaped galaxies in the early Universe.
Journal Reference:
- Mengyuan Xiao, Xhristina Williams, Pascal Oesch et al. PANORAMIC: Discovery of an ultra-massive grand-design spiral galaxy at z ∼ 5.2. Astronomy & Astrophysics. DOI: 10.1051/0004-6361/202453487
