The Two-faced Whirlpool Galaxy
01.13.11

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These images by NASA's Hubble Space Telescope show off two
dramatically different face-on views of the spiral galaxy M51,
dubbed the Whirlpool Galaxy.
The image at left, taken in visible light, highlights the
attributes of a typical spiral galaxy, including graceful, curving
arms, pink star-forming regions, and brilliant blue strands of
star clusters.
In the image at right, most of the starlight has been removed,
revealing the Whirlpool's skeletal dust structure, as seen in
near-infrared light. This new image is the sharpest view of the
dense dust in M51. The narrow lanes of dust revealed by
Hubble reflect the galaxy's moniker, the Whirlpool Galaxy, as if
they were swirling toward the galaxy's core.
To map the galaxy's dust structure, researchers collected the
galaxy's starlight by combining images taken in visible and
near-infrared light. The visible-light image captured only some
of the light; the rest was obscured by dust. The near-infrared
view, however, revealed more starlight because near-infrared
light penetrates dust. The researchers then subtracted the total
amount of starlight from both images to see the galaxy's dust
structure.
The red color in the near-infrared image traces the dust, which
is punctuated by hundreds of tiny clumps of stars, each about
65 light-years wide. These stars have never been seen before.
The star clusters cannot be seen in visible light because dense
dust enshrouds them. The image reveals details as small as 35
light-years across.
Astronomers expected to see large dust clouds, ranging from
about 100 light-years to more than 300 light-years wide.
Instead, most of the dust is tied up in smooth and diffuse dust
lanes. An encounter with another galaxy may have prevented
giant clouds from forming.
Probing a galaxy's dust structure serves as an important
diagnostic tool for astronomers, providing invaluable
information on how the gas and dust collapse to form stars.
Although Hubble is providing incisive views of the internal
structure of galaxies such as M51, the planned James Webb
Space Telescope (JWST) is expected to produce even crisper images.
Researchers constructed the image by combining visible-light
exposures from Jan. 18 to 22, 2005, with the Advanced
Camera for Surveys (ACS), and near-infrared light pictures
taken in December 2005 with the Near Infrared Camera and
Multi-Object Spectrometer (NICMOS).
Credit for the NICMOS image: NASA, ESA, M. Regan and B.
Whitmore (STScI), and R. Chandar (University of Toledo)
Credit for the ACS image: NASA, ESA, S. Beckwith (STScI), and
the Hubble Heritage Team (STScI/AURA)
Image files and more information about M51 are available on:
http://hubblesite.org/news/2011/03
http://www.nasa.gov/hubble
The Hubble Space Telescope is a project of international cooperation between
NASA and the European Space Agency. NASA's Goddard Space Flight Center manages
the telescope. The Space Telescope Science Institute (STScI) conducts Hubble
science operations. STScI is operated for NASA by the Association of
Universities for Research in Astronomy, Inc., in Washington, D.C.
Ray Villard/Donna Weaver
Space Telescope Science Institute, Baltimore, Md.
410-338-4514/410-338-4493
villard@stsci.edu/dweaver@stsci.edu
Michael Regan
Space Telescope Science Institute, Baltimore, Md.
410-338-4769
mregan@stsci.edu