The X-shaped Bulge of the Milky Way revealed by WISE

Understand

The Milky Way bulge has a boxy/peanut morphology and an X-shaped structure.

• This X-shape has been revealed by the `split in the red clump' from star counts along the line of sight toward the bulge, measured from photometric surveys.
• This boxy, X-shaped bulge morphology is not unique to the Milky Way and such bulges are observed in other barred spiral galaxies.
• N-body simulations show that boxy and X-shaped bulges are formed from the disk via dynamical instabilities.