Astronomy Picture of the Day
February 08, 2013
This image was taken by the Herschel Space Observatory and it shows our closest neighboring spiral galaxy – Andromeda, also known as M31. This galaxy is located about 2.5-million light-years from Earth and is about 200,000 light-years across.
This image depicts our large friend in infrared and is, obviously, in false color. Here, you can see the dust lanes in some amazing detail. Contrary to ‘common sense’ the redder regions show cooler gas and dust whereas the bluer regions are hotter. The dust in the outer regions of Andromeda is cooler because stars are more spars and the outer regions of a galaxy tend to be cooler because they are far away from the more crowded core. That brings me to me second explanation, regions near the center of the galaxy tend to be hotter because it’s more compact and there tend to me more stars.
In this image, you can also see regions of star formation scattered throughout the galaxy.