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Like early explorers mapping the continents of our globe, astronomers are
busy charting the spiral structure of our galaxy, the Milky Way. Using
infrared images from NASA's Spitzer Space Telescope, scientists have
discovered that the Milky Way's elegant spiral structure is dominated by
just two arms wrapping off the ends of a central bar of stars. Previously,
our galaxy was thought to possess four major arms.
This artist's concept illustrates the new view of the Milky Way, along
with other findings presented at the 212th American Astronomical Society
meeting in St. Louis, Mo. The galaxy's two major arms (Scutum-Centaurus
and Perseus) can be seen attached to the ends of a thick central bar,
while the two now-demoted minor arms (Norma and Sagittarius) are less
distinct and located between the major arms. The major arms consist of the
highest densities of both young and old stars; the minor arms are
primarily filled with gas and pockets of star-forming activity.
The artist's concept also includes a new spiral arm, called the "Far-3
kiloparsec arm," discovered via a radio-telescope survey of gas in the
Milky Way. This arm is shorter than the two major arms and lies along the
bar of the galaxy.
Our sun lies near a small, partial arm called the Orion Arm, or Orion
Spur, located between the Sagittarius and Perseus arms.
