The Milky Way in motion: gauging stellar trajectories that shape the Galactic thin disc

TL;DR

This study investigates the orbital evolution of stars in the Milky Way's thin disc, revealing that most stars undergo churning, with migration patterns influenced by chemical composition and Galactic structures.

Contribution

The paper introduces refined chemical-evolution models and applies a generalized additive model to estimate stellar birth radii, distinguishing between churning and blurring mechanisms in stellar migration.

Findings

Approximately 75% of stars exhibit churning-driven migration.

Metal-rich stars tend to migrate outward, while metal-poor stars migrate inward.

Migration patterns vary with chemical groups, indicating interactions with Galactic structures.

Abstract

As stars traverse the Milky Way, their orbits evolve through perturbations that alter their orbital radii. These changes arise from two mechanisms: churning, which modifies angular momentum, and blurring, which induces eccentric orbits without major angular momentum change. To assess whether churning or blurring dominates the dynamical evolution of Gaia-ESO stars, we refine Galactic chemical-evolution models by constructing finer grids that span a wider age range. Using a generalised additive model (GAM), we estimate stellar birth radii beyond the limits of binned metallicity models and compare them with dynamical parameters derived from Gaia parallaxes and proper motions, and Galpy. Our metallicity-stratified sample, grouped through hierarchical clustering of 21 chemical abundances, reveals clear migratory signatures: metal-rich stars formed in the inner disc preferentially move outwards, while more metal-poor stars formed at larger radii tend to migrate inwards. About 75% of stars show signs of churning, while the remainder are largely undisturbed or shaped by blurring. These patterns vary among chemical groups, likely reflecting interactions with the Galactic bar and spiral arms.