About 10% of the stars in the solar neighborhood belong to a large group that exhibits an oddly distinctive collective motion. Known as the Hercules stream, the group includes stars that are moving away from the center of the galaxy while falling behind the galaxy’s general rotation. The cause of that motion is the subject of a new study by Angeles Pérez-Villegas and her colleagues at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany.

New stars typically condense with other new stars out of the same dense cool region of gas and dust. Because stars are born more or less around the same time, they inherit the motion around the galaxy of their birthplace. The Hercules stream is different. Spectroscopic observations have revealed that it’s made up of stars of widely different ages. Whatever is causing the streaming motion operates across large scales of time and space.

One...

You do not currently have access to this content.