The Milky Way was built up over billions of years, partly from smaller galaxies that it absorbed. Stars born at different times and places differ in chemical make-up and in the way they orbit the Galaxy, and many of these differences persist for most of a star's life. Galactic archaeology measures these properties, and ages where possible, for large samples of stars, then sorts the stars into the populations that record how the Galaxy was put together.
Loading 160,000 stars
160,000 red giants from Gaia DR3 within five kiloparsecs of the Sun, with a ring every kiloparsec.
Data: red giants of Andrae, Rix and Chandra 2023 with metallicities from Ardern-Arentsen et al. 2025, from Gaia Data Release 3.
Using the second Gaia data release, Helmi and colleagues showed in 2018 that the inner stellar halo is dominated by debris from one galaxy, Gaia-Enceladus, whose merger with the Milky Way ESA dates to about 10 billion years ago. Ages can come from asteroseismology. Combining Kepler oscillations with APOGEE spectra for almost 5,400 red giants, Miglio and colleagues (2021) found that the nearly 400 alpha-rich giants of the chemically defined thick disc are about 11 billion years old, with 95 per cent of them formed within about 1.5 billion years.
Where I come in
I started my PhD at IA and the University of Porto in September 2022, on machine learning for Galactic archaeology. My 2025 paper in Astronomy and Astrophysics tested a method based on UMAP and HDBSCAN that separates thin-disc, thick-disc, halo and accreted stars by age, chemistry and motion, using synthetic Gaia samples built from the FIRE-2 simulations. Since February 2026 I have developed the machine-learning pipelines of ArqueoGal, an FCT exploratory project led by Tiago L. Campante.