Free Astronomy Magazine September-October 2025

28 SEPTEMBER-OCTOBER 2025 ASTRO PUBLISHING by NASA/ESA/CSA Abigail Major & Hannah Braun Webb digs into structural origins of disk galaxies P resent-day disk galaxies often contain a thick, star-filled outer disk and an embedded thin disk of stars. For instance, our own Milky Way galaxy’s thick disk is approxi- mately 3,000 light- years in height, and its thin disk is roughly 1,000 light- years thick. How and why does this dual disk struc- ture form? By ana- lyzing archival data from multiple obser- vational programs by NASA’s James Webb Space Tele- scope, a team of as- tronomers is closer to answers, as well as understand- ing the origins of disk galaxies in general. The team carefully identi- fied, visually verified, and analyzed a statistical sample of 111 edge-on disk galaxies at various periods — up to 11 billion years ago (or ap- proximately 2.8 billion years after “This unique measurement of the thickness of the disks at high red- shift, or at times in the early uni- verse, is a benchmark for theoretical study that was only possible with Webb,” said Takafumi Tsukui, lead author of the paper and a re- searcher at the Australian National the big bang). This is the first time scientists have investigated thick- and thin-disk structures spanning such vast distances, bridging the gap between observers probing the early universe and galactic archae- ologists seeking to understand our own galaxy’s history.