Astronomers find “spaghetti” twirling around in galaxy
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” — made this discovery in early January, finding new evidence
suggesting the existence of three more star streams in the outer galaxy.
Days later, Case Western Reserve University astronomer Heather Morrison
announced the group’s findings during a presentation to more than 2,000
scientists at the joint annual meeting of American Astronomical Society
and the American Association of Physics Teachers in San Diego.
Morrison will talk about the new discoveries during a CWRU Physics
Colloquium at 4:30 p.m. Thursday, February 1 in 301 Rockefeller Hall.
“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 Morrison.
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.
