The Sagittarius impact as an architect of spirality and outer rings in the Milky Way

Understand

Like many galaxies of its size, the Milky Way is a disk with prominent spiral arms rooted in a central bar, although our knowledge of its structure and origin is incomplete.

• Traditional attempts to understand the Galaxy's morphology assume that it has been unperturbed by major external forces.
• Here we report simulations of the response of the Milky Way to the infall of the Sagittarius dwarf galaxy (Sgr), which results in the formation of spiral arms, influences the central bar and produces a flared outer disk.
• Two ring-like wrappings emerge towards the Galactic anti-Center in our model that are reminiscent of the low- latitude arcs observed in the same area of the Milky Way.