This combination of photos made available by NASA shows the spiral galaxy Messier 81 (M81) viewed in two different types of infrared wavelengths showing the the light from the stars in the galaxy, left, and the distribution of dust particles without starlight, captured by the Spitzer Space Telescope. The dust particles are composed of silicates (chemically similar to beach sand), carbonaceous grains and polycyclic aromatic hydrocarbons and trace the gas distribution in the galaxy.