The dynamical effects of the bar on the Galactic thin and thick disks

The Milky Way is our Galaxy, the home to the Earth and the Sun. Most of the stars in the Milky Way move on trajectories that are almost circular and are organized in a flattened structure called “thin disk”. A smaller fraction of stars have different trajectories, more elongated orbits and extend in a wide stratum called “thick disk”. The stars in the thin and thick disks travel also at different speeds. As many galaxies, the Milky Way has a stellar bar in its center and spiral arms formed by stars, gas and dust. The bar and the spiral arms influence the velocity of the stars in the Milky Way. In particular, we find that the effect of the bar is to induce the appearance of two groups of stars near the Sun: one moves inwards and another one moves outwards in the Milky Way. These groups exist for both disks. We classify the stars’ orbits with a technique that calculates the times they need to rotate in the Milky Way. In particular, we expect a similar fraction of the stars in the thin and thick disks that have an orbit strongly modified by the bar. Recent observations show how those stars that are closer to the Milky Way center tend to move outwards faster than those located at larger distances. Our predictions on the effect of the bar on the stars of the thin and thick disks agree with these observations.