Herschel Image of M31
This image, taken at far-infrared wavelengths by ESA's Herschel Space Observatory, shows the Andromeda galaxy, also known as M31, the nearest major galaxy to the Milky Way.
Due to its proximity to us, Andromeda is ideally suited for investigations of star formation and evolution on the global scale of an entire galaxy similar to our own Milky Way with a degree of detail that cannot be achieved through observations of other, more distant galaxies.
Observing the Universe at far-infrared and submillimetre wavelengths, Herschel is sensitive to the cold material that represents a window on the early phases of the formation of stars.
The data collected by Herschel in the far-infrared domain probe the cold dust component of the interstellar medium (ISM), the mixture of (mostly) gas and dust from which new stars originate in galaxies. The dust, heated by young and massive stars as they form, shines brightly in the wavelength range explored by Herschel and traces the overall distribution of the ISM, revealing its intricate structure. The image highlights how the mixture of dust and gas in M31 exhibits a complex pattern organised in spiral arms and at least five concentric rings. In addition, a series of other smaller-scale features, such as bright arcs and dark “holes”, disclose regions where the star formation activity appears to be more or less intense. The large rings of dust that encircle the centre of the galaxy may be the result of a smaller galaxy having collided with Andromeda some time in the past.
The image shown here, the most detailed ever obtained of M31 at a far-infrared wavelength of 250 micron (500 times longer than that of yellow light), was taken with the SPIRE instrument on board Herschel, and is based on a total observing time of 18 hours. The field of view of the image shown is 1.5x2 degrees, although a larger area was actually observed.
The image was obtained during Christmas 2010.