From Symmetry/Breaking: “Scientists Discover that Milky Way Was Struck Some 100 Million Years Ago, Still Rings Like a Bell”
June 28, 2012 | 11:24 am
“Our galaxy, the Milky Way, is a large spiral galaxy surrounded by dozens of smaller satellite galaxies. Scientists have long theorized that occasionally these satellites will pass through the disk of the Milky Way, perturbing both the satellite and the disk. A team of astronomers from Canada and the United States have discovered what may well be the smoking gun of such an encounter, one that occurred close to our position in the galaxy and relatively recently, at least in the cosmological sense.
Stars in the disk of the Milky Way move up and down at a speed of about 20-30 kilometers per second while orbiting the center of the galaxy at a brisk 220 kilometers per second. Image: Fermilab
‘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,’ said Larry Widrow, professor at Queen’s University in Canada. ‘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.’
The discovery is based on observations of some 300,000 nearby Milky Way stars by the Sloan Digital Sky Survey. Stars in the disk of the Milky Way move up and down at a speed of about 20-30 kilometers per second while orbiting the center of the galaxy at a brisk 220 kilometers per second. Widrow and his four collaborators from the University of Kentucky, the University of Chicago and Fermi National Accelerator Laboratory have found that the positions and motions of these nearby stars weren’t quite as regular as previously thought.”
The results have been published in The Astrophysical Journal Letters.
See the full article here.