Nearing the end of its mission, ESA's Herschel Space Observatory has delivered a highly detailed map of extremely cold gas and dust in the iconic Andromeda Galaxy.
We've seen so many images of the grand, stately Andromeda Galaxy (Messier 31) that we sometimes forget that this giant pinwheel is alive with activity and, especially, star formation. But this just-released view, taken by the European Space Agency's Herschel spacecraft, reveals M31 in a new light.
Specifically, the space observatory recorded the galaxy's appearance at far-infrared wavelengths. The longer the wavelength, the colder the matter, and the dark-red lanes in the disk correspond to some of the very coldest dust in the galaxy (only a few tens of degrees above absolute zero). That's where future generations of stars will be born. By contrast, the bluish appearance of M31's central bulge shows that it is somewhat warmer and already dense with older stars.
Located 2½ million light-years away, the Andromeda Galaxy is about 200,000 light-years across (twice the size of our Milky Way Galaxy). Herschel's view reveals at least five concentric rings in its spiral arms. In between these are dark gaps where star-forming regions are absent.
This isn't the first time Herschel's 3.5-meter optics have been directed toward M31. Compare this view with another infrared portrait taken in late December 2010.
Launched in May 2009, the spacecraft was originally known as the Far InfraRed and Submillimetre Telescope (FIRST) but later renamed for Sir William Herschel, who in 1800 discovered infrared radiation. The spacecraft has given astronomers their most detailed views to date of cosmic targets in far-infrared and submillimeter wavelengths (from 60 to 670 microns).
While this wasn't Herschel's first look at the Andromeda Galaxy, it will likely be its last. The spacecraft is about to run out of the liquid helium that chills its optics and detectors. Once the helium is gone, now expected to occur within the next two months, the mission will end.
Here's an ESA website where you can get more information about Herschel and its mission.