Disk galaxies, like our own Milky Way galaxy, commonly consist of both a thick and thin disk of stars — each with different features, including stellar population and movement. Three major theoretical scenarios have been proposed to explain the formation mechanisms and timing of thick and thin disks.

A team of astronomers has recently investigated the structure of disk galaxies by sifting through multiple surveys from NASA’s James Webb Space Telescope. This extensive sample includes over 100 edge-on disk galaxies up to roughly 11 billion years ago. The team’s analysis aligns with one of the three scenarios, suggesting that thick stellar disk formation occurs first, and thin stellar disk formation follows. When this happens in a galaxy’s formation history depends on the galaxy’s mass.