The James Webb Space Telescope has identified a “bulge fossil fragment” in the Milky Way’s core, offering fresh clues about galaxy assembly. Researchers focused on Terzan 5, a dense stellar region long obscured by dust, and combined new Webb data with archival Hubble images to reassess its nature. The observations captured infrared spectra that pierce the dust, revealing the cluster’s complex composition.

Analysis revealed Terzan 5 is not a simple globular cluster; instead it hosts at least four stellar populations spanning ages from 12.5 billion to 2.5 billion years. Two ancient groups formed 12.5 Gyr and 4.7 Gyr ago, while younger cohorts emerged 3.8 Gyr and 2.5 Gyr ago, indicating multiple star‑formation bursts. Such a layered history challenges the traditional view of bulge formation as a single, rapid collapse.

University of Bologna lead Francesco R. Ferraro calls Terzan 5 a “bulge fossil fragment,” a relic of the primordial clumps that merged to build the galactic bulge. Co‑author Barbara Lanzoni links the finding to simulations where early‑universe gas disks fragmented, migrated inward, and coalesced. The study, published in Astronomy & Astrophysics, reshapes how astronomers trace the Milky Way’s formative phases significantly.