This Spitzer Space Telescope photograph shows the Serpens South star cluster – a relatively dense group of 50 young stars, 35 of which are protostars just beginning to form. Tints of green in the image represent hot hydrogen gas excited when high-speed jets of gas ejected by infant stars collide with the cool gas in the surrounding cloud. Wisps of red in the background are organic molecules called polycyclic aromatic hydrocarbons (PAHs). Credit: NASA/JPL-Caltech/L. Allen (Harvard-Smithsonian CfA) & Gould's Belt Legacy Team