Top row:

1000 stars (test particles) are uniformly distributed on  a circle at a radius near an Outer Lindblad Resonance (OLR) (left) and close to the Corotation radius (CR) (right). Orbits are integrated in a logarithmic potential (flat rotation curve as in the Milky Way) and a perturbation from a spiral arm moving with an angular velocity placing the given radius near the indicated resonance. You can see that orbits are regular when only one spiral set is present.

Bottom row:

Same as the top row but including perturbations from two spiral waves moving with different angular velocities (or pattern speeds). The pattern speeds are chosen to place the ring of stars close to the Outer Lindblad Resonance of the 4-armed spiral and the Corotation of the 2-armed spiral at the same time (left panel) or close to the Inner Lindblad Resonance of the 4-armed spiral and the Corotation of the 2-armed spiral (right panel).

When two perturbations are present at the same time, the dynamics is stochastic and a net migration inward is seen for the OLR+CR, while a net migration outward is found for the OLR+CR combination. Multiple spirals are always seen in numerical simulations and inferred from observations, suggesting that resonance overlap effects are taking place in all disk galaxies.

Click here to see how radial migration affects the disk thickness.

Click here to see how radial migration can be linked to a chemo-kinematic relation in the Milky Way.