The
ring-like swirls of dust filling the Andromeda galaxy stand out
colorfully in this new image from the Herschel Space Observatory, a
European Space Agency mission with important NASA participation.
The glow seen here comes from the longer-wavelength, or far, end of the
infrared spectrum, giving astronomers the chance to identify the very
coldest dust in our galactic neighbor. These light wavelengths span from
250 to 500 microns, which are a quarter to half of a millimeter in
size. Herschel's ability to detect the light allows astronomers to see
clouds of dust at temperatures of only a few tens of degrees above
absolute zero. These clouds are dark and opaque at shorter wavelengths.
The Herschel view also highlights spokes of dust between the concentric
rings.
The colors in this image have been enhanced to make them
easier to see, but they do reflect real variations in the data. The
very coldest clouds are brightest in the longest wavelengths, and
colored red here, while the warmer ones take on a bluish tinge.
These data, together with those from other observatories, reveal that
other dust properties, beyond just temperature, are affecting the
infrared color of the image. Clumping of dust grains, or growth of icy
mantles on the grains towards the outskirts of the galaxy, appear to
contribute to these subtle color variations.
These observations
were made by Herschel's spectral and photometric imaging receiver
(SPIRE) instrument. The data were processed as part of a project to
improve methods for assembling mosaics from SPIRE observations. Light
with a wavelength of 250 microns is rendered as blue, 350-micron is
green, and 500-micron light is red. Color saturation has been enhanced
to bring out the small differences at these wavelengths.
Image credit: ESA/NASA/JPL-Caltech/NHSC
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