Milky Way flutters as it spins

As the Milky Way spirals around a central, supermassive black hole, the galaxy may also flutter like a flag from top to bottom.

Astronomers led by Mary Williams of the Leibniz Institute for Astrophysics in Potsdam, Germany, tracked stars in the suburbs of the solar system and found that the stars sway in and out along the galaxy’s north-south axis. The team describes the motion in a paper accepted for publication in the Monthly Notices of the Royal Astronomical Society.

What’s causing the Milky Way’s flutter is unclear, but the astronomers suggest the motion could come from the movement of the galaxy’s spiral arms or from a collision with a smaller galaxy, both of which would influence scientists’ model of how the galaxy moves.