Like a celestial bully, the Milky Way may have ripped apart a smaller galaxy billions of years ago and scattered its stars into a faint surrounding ring.
A survey scanning the outskirts of the Milky Way has found a belt of stars different in chemistry and in motion from stars within the galaxy, suggesting that they are the remnants of a galactic collision that may have occurred 10 billion years ago.
The ring, about 120,000 light-years across, is shaped like a doughnut with the Milky Way in its center.
"This is something new that we had not expected to find," said Heidi Jo Newberg of Rensselaer Polytechnic Institute in Troy, N.Y.
She and Brian Yanny of the Fermi National Accelerator Laboratory discovered the ring during the Sloan Digital Sky Survey, a project to plot the position and brightness of 100 million celestial objects.
A European team, using different instruments, has confirmed the existence of the ring.