Credit: NASA/JPL-Caltech

This newly-processed infrared image of the Andromeda galaxy uses data from NASA’s now-retired Spitzer Space Telescope to show off the disk of stars and clouds of dust that fill our Milky Way Galaxy’s largest neighbor. The image spans a wide swath of sky nearly 3.8 degrees across, which is close to the width of eight full moons stacked side-by-side.

Infrared light provides a powerful tool for studying how new generations of stars are being formed in galaxies like Andromeda. Dust clouds in visible light are only seen as they block the light of background stars, but light up at longer infrared wavelengths.

The dust clouds in Andromeda form a ring running through the pancake-like disk of stars, along which we can see many areas in which new stars are being formed. However, arcs of dust found near the center of the galaxy provide a hint of the supermassive black hole that lies here.

In this image, starlight glows at wavelengths of 3.6 & 4.5 microns, blended in colors of blue and cyan. Dust dominates at 8 microns, tracing the glow of polycyclic aromatic hydrocarbons that light up under the illumination of the surrounding stars. The thermal glow of dust at 24 microns is added in as green, blending with the red dust channel to produce orange-yellow highlights at the hottest dust clouds associated with newly-forming stars.

Data from NASA’s Wide-field Infrared Space Explorer (WISE) fills in the areas not mapped by Spitzer, mostly containing foreground stars in the Milky Way.