PM Updated 1/10/2006 7:45
Astronomers may have reason for Milky Way's
Vergano, USA TODAY
WASHINGTON — A
mysterious lumpiness in the Milky Way Galaxy, home to our own solar system,
might be caused by the gravitational pull of passing galaxies, astronomers
rendering of the Milky Way galaxy.
①『Galaxies are islands
of stars in space. Each one is home to tens of millions of stars, including our
own sun, which resides in the outer reaches of the disc-shaped Milky Way. The
Milky Way is shaped just like many others, but it has a warp that has defied
explanation for five decades, says astronomer Evan Levine of the University of
"It's not just that our
galaxy is lopsided in a sense. The fact is that it has a special shape," says
Levine, who spoke Monday at the American Astronomical Society meeting.
Leo Blitz, compares the galaxy's shape to the tipped brim of a fedora. On the
galaxy's northern side, stars and gas bulge more than 16,000 light-years above
the galactic disc. (One light-year equals about 5.9 trillion miles.) In the
southern sky, it dips about 3,200 light-years.
long ago that a smaller pair of passerby galaxies, the Large and Small
Magellanic Clouds, were bending the Milky Way through a tidal pull, much like
the moon raises tides on Earth. But those two small galaxies do not weigh
enough to have that kind of pull, so astronomers ruled them out as a reason.
③『But those same
galaxies are indeed behind the warping, Levine says. Decades ago, astronomers
did not know that a ring of "dark matter," 10 times heavier than the normal
matter that makes up stars and planets, surrounds our galaxy. Astronomers
disagree on what dark matter is, but most see it as a collection of exotic
particles that give off very little light.
Analysis by the two
astronomers reveals that the nearby galaxies churn up a wake in that
dark-matter ring, "plowing through them like a boat," Blitz says. In turn, the
gravitational pull of that wake twists the shape of our galaxy.
Other galaxies show
similarly warped structures, Levine says. 』
dwarf galaxies and dark matter distort galaxies helps astronomers understand
how such structures arise in the universe and perhaps answer fundamental
questions about the origins of stars and planets.
The Milky Way's warping
is a well-known phenomenon, says astronomer Robert Lupton of Princeton
University. He is part of the Sloan Digital Sky Survey effort, an astronomical
atlas of galaxies. His team found another lump in our galaxy, the remains of
another dwarf galaxy. But those lumpy remains are much farther out.