The elegant spiral galaxy Andromeda, named after the mythical Greek princess known for her beauty, also known as Messier 31, lies 2 million light-years away, and is the closest large galaxy to our own Milky Way. It is estimated to have up to one trillion stars, whereas the Milky Way contains hundreds of billions. Recent evidence suggests Andromeda's overall mass may in fact be less than the mass of the Milky Way, when dark matter is included.
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.
In both views, warmer dust is highlighted in the central regions by different colors. New stars are being born in this central, crowded hub, and throughout the galaxy's rings in dusty knots. Spokes of dust can also be seen between the rings. One view, seen at www.jpl.nasa.gov/spaceimages/details.php?id=PIA16682 , is a mosaic of data from Herschel's Photodetecting Array Camera and Spectrometer (PACS) and spectral and photometric imaging receiver (SPIRE).
The second view, seen at www.jpl.nasa.gov/spaceimages/details.php?id=PIA16681 , shows data from only the SPIRE instrument, which captures the longest of wavelengths detectable by Herschel.
The Daily Galaxy via NASA
Image Credit: ESA/Herschel/PACS & SPIRE Consortium, O. Krause, HSC, H. Linz