Astronomy Colloquium

The Milky Way can indeed serve as a Galaxy model organism to tell us which physical processes shape the current structure and stellar content of galaxies: what sets the overall radial profile of the disk, which the present-day orbital of any star, and how much formation memory does the Milky Way's disk retain?  We can now draw on global Galactic stellar surveys that constrain orbits, abundances and ages. I will show how modelling these data now shows that global radial orbit migration is a very strong effect that decisively shapes the structure of the Milky Way's disk. If the Milky Way is typical in this respect this explains why galaxy disk profiles are exponential. And I will sketch how Gaia is about to tell us in far  more detail the mechanisms that drive this orbit evolution.