AI and the World's Hard Problems · Astronomy & space · arXiv · 2026-10-23
Impact of Gaia-Sausage-Enceladus merger revealed by a single cosmic clock: thick-to-thin disc transition, gas disc shrinking and bar formation
Whether the Milky Way's bar formed in connection with the Gaia-Sausage-Enceladus (GSE) merger has been unresolved, because the two epochs were dated with different stellar tracers. The researchers recalibrated the Mira period-age relation onto the APOGEE red-giant age scale and fit Gaia DR3 proper motions of 2394 Mira variables. This places the nuclear disc's star-formation peak at 8.5 to 10.5 billion years ago, overlapping with the GSE-induced starburst, the thick-to-thin disc transition and gas-disc contraction, which suggests GSE may have seeded bar formation.