This infrared view, captured by Spitzer Space Telescope, clearly outlines the spiral arms of Messier 31, the Andromeda Galaxy. The arms are filled with infrared-emitting gas and dust that give birth to new stars. Many newborn stars in the arms are bright and massive, so they help outline a galaxy's spiral arms. [NASA/JPL-Caltech/K. Gordon (University of Arizona)]
Find out more in our radio program entitled Spiral Arms.