Milky Way Still Ringing Like A Bell After 100 Million Year Old Collision

By Chelsea Whyte on June 30, 2012 12:30 AM EDT

milky way
In the night sky, the Milky Way looks serene. But scientists have measured the stars that make up the disc of our galaxy and they are reverberating like a ringing bell. (Photo: Creative Commons: madmiked)

Our home galaxy, the Milky Way, is still reverberating after a cosmic crash by a small galaxy or massive dark matter structure that happened 100 million years ago.

Observations of 300,000 nearby Milky way stars by the Sloan Digital Sky Survey showed researchers that the positions of these stars were not as regular are previously thought. The Sloan Digital Sky Survey (SDSS) found that while stars in the disk of the Milky Way orbit the center of the galaxy at a rapid 136 miles per second, they also move up and down at a speed of about 12-18 miles per second.

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"We clearly observe unexpected differences in the Milky Way's stellar distribution above and below the Galaxy's mid-plane having the appearance of a vertical wave - something that nobody has seen before," said Queen's University physicist Larry Widrow, lead researcher on the project, according to Space Ref.

"Our part of the Milky Way is ringing like a bell," said Brian Yanny, of the Department of Energy's Fermilab, according to Symmetry Magazine. "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."

There are more than 20 known visible satellite galaxies that circle the center of the Milky Way, with masses ranging from one million to one billion solar masses. And with six times as much dark matter in the universe as ordinary, visible matter, there may also be invisible satellites made of dark matter.

Computer simulations indicate that over the next 100 million years or so, our galaxy will "stop ringing" and the vertical motions of stars in the solar neighborhood will revert back to their equilibrium orbits - unless we get hit again.

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