May 17, 2001 CLEVELAND -- Circulating the Milky Way is a stream of stars that has wound itself around the galaxy like a strand of spaghetti.
A consortium of researchers from three continents -- called the "Spaghetti Collaboration" -- found new evidence suggesting the existence of three more star streams in the outer galaxy.
"It is exciting news to know that there are star streams in the outer galaxy, and things are messier, more beautiful, and more dynamic than originally thought," says Heather Morrison, an astronomer at Case Western Reserve University.
She works with collaborators from CWRU (Jiayang Sun, associative professor of statistics), Massachusetts Institute of Technology (John Arabadjis), the University of Michigan (Mario Mateo), the Max Planck Institute in Germany (Amina Helmi), the Mt. Stromlo Observatory in Australia (Ken Freeman and John Norris), and the Steward Observatory (Paul Harding and Ed Olszewski). Their National Science Foundation-funded project is called "Mapping the Galactic Halo."
The spaghetti stream stretches from 60 degrees above the night horizon in June to 45 degrees below the horizon line, explains Morrison. "It covers a lot of the sky," she says.
Since 1994 astronomers have known there is a new dwarf galaxy in the Milky Way's neighborhood. The astronomers found the Sagittarius Dwarf on the far side of the Milky Way. Because it is hidden behind the dust and stars that fill the galaxy's disk, it was difficult for astronomers to see the small galaxy, which is one-hundredth the mass of the Milky Way. It is on the far edge of our galaxy's disk, which is shaped like a Mexican tortilla, says Morrison.
Astronomers believe that the Sagittarius Dwarf was "slurped up" by gravitational forces of the Milky Way at its formation 10-15 billion years ago. As the Milky Way's gravitational tidal forces continue to pull on the dwarf galaxy, it begins to stretch it out in a tidal force that leaves behind a tidal tail. As it continues to orbit the galaxy, it continues to leave strings of stars in its wake.
When astronomers started plotting the movement of the stars, Morrison says they found "a clump of stars moving together like a football team" at the same speed and distance from the Milky Way's center. They also found evidence for three other clumps at different distances and speeds, she adds.
"The Sagittarius Dwarf is a wimpy galaxy. Astronomers had to look hard to find it," says Morrison. The dwarf galaxy is approximately 75,000 light years from earth. It is the first of several small neighborhood galaxies in line to be "gobbled up" by the large Milky Way. The Large and Small Magellanic Clouds will have a similar destiny in the future.
"The star streams are important. They will help astronomers determine the mass of the Milky Way and the strength of its gravitational force," says Morrison. Some day that information may prove helpful as future residents of the Milky Way many billion of years in the future will see our galaxy meet the Andromeda Galaxy at a spectacular dinner party.
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