The James Webb Space Telescope (JWST) has observed that galaxies form in two main stages: a chaotic thick disk followed by a calmer, thin disk. This pattern was identified in 111 edge-on galaxies, including those from 10 billion light-years away.
The research, led by Takafumi Tsukui, shows that the Milky Way's layered structure is part of a broader galactic trend. The thin disk, home to younger stars, forms within the older, thick disk, which contains more primitive stars.
JWST's sharp vision allowed astronomers to identify these disks in distant galaxies, confirming the two-stage formation process. The study, published in the journal Monthly Notices of the Royal Astronomical Society on June 26, 2025, estimates the thin disk formation time for Milky Way-sized galaxies to be around 8 billion years ago.