The formation and survival of the Milky Way's oldest stellar disk

Understand

It remains a mystery when our Milky Way first formed a stellar disk component that survived and maintained its disk structure from subsequent galaxy mergers.

• We present a study of the age-dependent structure and star formation rate of the Milky Way's disk using high-alpha stars with significant orbital angular momentum that have precise age determinations.
• Our results show that the radial scale length is nearly independent of age, while the vertical scale height experienced dramatic evolution.
• A disk-like geometry presents even for populations older than 13 Gyr, with the scale height-to-length ratio dropping below 0.5 for populations younger than 12.5 Gyr.