Disk Heating and Stellar Migration in Galaxies

We show that a typical star is unlikely to migrate from its galacto-centric radius of birth by more than about 5% over its lifetime. Radial migration, or a secular change in a star’s angular momentum, is caused by stochastic scattering by spiral waves and by dense gas complexes. The expected change in angular momentum is related to the radial action acquired by the star from these processes and is consequently limited by the measured radial velocity dispersion within the disk. Our conclusion conflicts with recent claims that the solar system was formed some 2 kpc interior to its present position, which were advanced to account for abundance anomalies in the Sun and solar system dust in the context of a well-mixed and steadily polluting ISM. We suggest that abundance variations in nearby stars reflect intrinsic scatter in the metallicity of the ISM at any one galacto-centric radius and time.