Our Milky Way galaxy appears to have flipped 90 degrees long ago. But why?

An image of the Milky Way with a bunch of yellow arrows going toward and through it.

The Milky Way's spiral disk may have flipped over by 90 degrees, in turn altering the solar system's orbit around the center of the galaxy.

Spiral galaxies such as the Milky Way have two main, visible, structural components: a disk that encapsulates most of its stars, gas and the central black hole, and a more diffuse halo of older stars that encapsulates the disk.