ASTRO
In the literature: open
Relative roles of disk heating and radial migration
In plain words
Older stars in the disk move more randomly and many no longer orbit where they were born. How much of this comes from spiral arms, the bar, gas clouds or passing satellites is not settled.
Precise statement
Quantify the contributions of spiral arms, the bar, giant molecular clouds and satellites to the Milky Way age-velocity dispersion relation ($\sigma \sim t^{\beta}, \beta \sim 0.3 \text{ to } 0.5$) and to radial migration by churning at corotation, and determine the distribution of birth radii versus age, including the Sun's.
What would settle it
Birth-radius reconstruction from chemistry and ages for Gaia and spectroscopic samples, compared with simulations that separate the mechanisms.