Astronomers using the James Webb Space Telescope (JWST) have spotted two types of galaxy disks for the first time in galaxies as far back as 10 billion years ago. The discovery reveals that galaxies formed with a thick, chaotic disk before developing the calm, thin disk seen in modern spiral galaxies like the Milky Way.
Until now, scientists couldn’t distinguish the thin edge of a distant galaxy when viewed from the side due to limitations in previous telescopes. However, JWST’s sharp vision enabled researchers to observe 111 images of edge-on galaxies and identify both thick and thin disks.
The study found that more galaxies had a single thick disk in the early universe, while later epochs showed a two-layered structure with an additional thin disk component. This suggests that galaxies formed a thick disk first, followed by the formation of a thin disk within it. In massive galaxies, this thin disk appears to have formed earlier.
Researchers used data from ALMA and ground-based surveys to understand the sequential formation from thick to thin disks and estimated the thin disk formation time for Milky Way-sized galaxies to be around 8 billion years ago. This aligns with the Milky Way’s own formation timeline.
The study provides valuable insights into galaxy formation, shedding light on how galaxies form stars, build up elements essential for life, and evolve into their present shapes. The findings also help answer a key question in astronomy: was our galaxy’s formation typical or unique?
By studying distant galaxies using JWST, researchers can gain a better understanding of disk formation and refine our knowledge of how galaxies evolved over cosmic history.
Source: https://www.sciencedaily.com/releases/2025/06/250629033347.htm