Cosmic impact left Milky Way 'ringing'

KINGSTON, Ontario, June 28 (UPI) -- U.S. and Canadian astronomers say our Milky Way galaxy was struck by another galaxy or some large cosmic structure eons ago the left it "ringing like a bell."

Our Milky Way is a large spiral galaxy surrounded by dozens of smaller satellite galaxies, and astronomers have long suspected that occasionally these satellites will pass through the disk our home galaxy.

Now astronomers writing in The Astrophysical Journal Letters report observing what they consider strong proof of such a close encounter in the motions of some 300,000 Milky Way stars that are not as predictable and regular as they should be.

"We have found evidence that our Milky Way had an encounter with a small galaxy or massive dark matter structure perhaps as recently as 100 million years ago," Larry Widrow of Queen's University in Canada said.

"We clearly observe unexpected differences in the Milky Way's stellar distribution above and below the Galaxy's midplane that have the appearance of a vertical wave -- something that nobody has seen before."

Computer simulations suggest the observations are telling us something about recent events in the history of our galaxy, astronomers say.

"Our part of the Milky Way is ringing like a bell," as an aftereffect of some sort of cosmic entanglement, Brian Yanny of the U.s. Department of Energy's Fermilab said.

"But we have not been able to identify the celestial object that passed through the Milky Way. It could have been one of the small satellite galaxies that move around the center of our galaxy, or an invisible structure such as a dark matter halo."

Astronomers say their simulations suggest over the next 100 million years or so, our galaxy will "stop ringing" as the stars in the solar neighborhood revert back to their equilibrium orbits -- unless we get hit again.