The stars on the rim of the galaxy are going for a ride. They’re bobbing up and down like the horses on a merry-go-round. They’re also rippling outward, away from the center of the Milky Way.

The Milky Way consists of a thin disk of stars and gas that spans a hundred thousand light-years or more. For decades, we’ve known that the rim of the disk is warped like the brim of a wide hat. It’s bent upward on one edge, and downward on the opposite edge.

A recent study found that stars on those edges are moving along a big wave. Astronomers looked at the locations and motions of more than 20,000 bright young stars logged by the Gaia space telescope. The stars are as much as 45,000 light-years from the galactic center.

Gaia found that the stars are bobbing up and down as much as a thousand light-years above or below the plane of the galaxy. And they appear to be sliding outward at thousands of miles per hour.

The wave might have been created by a close approach of a smaller galaxy hundreds of millions of years ago. Its gravity disturbed the tranquility of the Milky Way’s outer precincts – sending the stars there for a ride.

Under dark skies, the Milky Way is in good view tonight. In early evening, it extends along the body of Cygnus, the swan, in the west-northwest; through M-shaped Cassiopeia, higher in the sky; then down between Orion and the twins of Gemini, in the east-southeast.

Script by Damond Benningfield