Galactic survey reveals a new look for the Milky Way (Forwarded)

University of Wisconsin-Madison

August 16, 2005

Galactic survey reveals a new look for the Milky Way
By Terry Devitt, trdevitt @ wisc.edu

With the help of NASA's Spitzer Space Telescope, astronomers have
conducted the most comprehensive structural analysis of our galaxy and
have found tantalizing new evidence that the Milky Way is much different
from your ordinary spiral galaxy.

The survey using the orbiting infrared telescope provides the fine details
of a long central bar feature that distinguishes the Milky Way from more
pedestrian spiral galaxies.

"This is the best evidence ever for this long central bar in our galaxy,"
says Ed Churchwell, a UW-Madison professor of astronomy and a senior
author of a paper describing the new work in an upcoming edition of
Astrophysical Journal Letters, a leading astronomy journal.

Using the orbiting infrared telescope, the group of astronomers surveyed
some 30 million stars in the plane of the galaxy in an effort to build a
detailed portrait of the inner regions of the Milky Way. The task,
according to Churchwell, is like trying to describe the boundaries of a
forest from a vantage point deep within the woods: "This is hard to do
from within the galaxy."

Spitzer's capabilities, however, helped the astronomers cut through
obscuring clouds of interstellar dust to gather infrared starlight from
tens of millions of stars at the center of the galaxy. The new survey
gives the most detailed picture to date of the inner regions of the Milky
Way.

"We're observing at wavelengths where the galaxy is more transparent, and
we're bringing tens of millions of objects into the equation," says Robert
Benjamin, the lead author of the new study and a professor of physics at
the University of Wisconsin-Whitewater.

The possibility that the Milky Way Galaxy has a long stellar bar through
its center has long been considered by astronomers, and such phenomena are
not unheard of in galactic taxonomy. They are clearly evident in other
galaxies, and it is a structural characteristic that adds definition
beyond the swirling arms of typical spiral galaxies.

The new study provides the best estimates for the size and orientation of
the bar, which are far different from previous estimates.

It shows a bar, consisting of relatively old and red stars, spanning the
center of the galaxy roughly 27,000 light years in length -- 7,000 light
years longer than previously believed. It also shows that the bar is
oriented at about a 45-degree angle relative to a line joining the sun and
the center of the galaxy.

Previously, astronomers debated whether a presumed central feature of the
galaxy would be a bar structure or a central ellipse -- or both. The new
research, the Wisconsin astronomers say, clearly shows a bar-like
structure.

"To date, this is the best evidence for a long bar in our galaxy,"
Benjamin asserts. "It's hard to argue with this data."

The Spitzer Space Telescope was lofted into orbit in August of 2003. It
consists of a telescope and three science instruments, including the
Infrared Array Camera, the primary instrument used for the new survey,
known as GLIMPSE for Galactic Legacy Mid-Plane Survey Extraordinaire.

NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif., manages the
Spitzer Space Telescope mission for NASA's Science Mission Directorate,
Washington, D.C. Science operations are conducted at the Spitzer Science
Center in Pasadena. JPL is a division of the California Institute of
Technology.

IMAGE CAPTION:
[http://www.news.wisc.edu/news/images...laxy_sun05.jpg (33KB)]
The Milky Way, it turns out, is no ordinary spiral galaxy. According to a
massive new survey of stars at the heart of the galaxy by Wisconsin
astronomers, including professor of astonomy Edward Churchwell and
professor of physics Robert Benjamin, the Milky Way has a definitive bar
feature -- some 27,000 light years in length -- that distinguishes it from
pedestrian spiral galaxies, as shown in this artist's rendering. The
survey, conducted using NASA's Spitzer Space Telescope, sampled light from
an estimated 30 million stars in the plane of the galaxy in an effort to
build a detailed portrait of the inner regions of the Milky Way.
Illustration courtesy: NASA/JPL-Caltech/R. Hurt (SSC/Caltech)