Interstellar clouds, infrared image. The two dark nebulae (upper left and upper right) are dense clouds of dust that harbour embryonic stars (red). A particularly large one, 20-50 times the size of the Sun, is seen in the middle of the snake shaped nebula. When the embryonic stars accumulate enough dust and gas, their nuclear reactions ignite. Their radiation ionises the surrounding gas (red/yellow area, lower right), which is then sculpted by their stellar winds. The supernova remnant (red, left) is the remains of a star that exploded, sending out matter and energy outwards in all directions, giving it a spherical shape. Image taken by NASA's Spitzer telescope.