Star life cycles, illustration

Life cycle of stars, illustration. From top to bottom are brown dwarf, main-sequence (red dwarf), main-sequence (more massive than red dwarfs), and finally giant stars. All begin from a spinning disc of gas and dust called a planetary nebula, hewn from an initially much larger gas cloud. Brown dwarfs simply fade with age, their diameters changing very little. Red dwarfs, once they have left the main-sequence, continually contract and end their existences as white dwarfs. Low-mass stars such as the Sun expand into red giants when they run out of reactive elements, then lose their outer layers to form a planetary nebula, leaving behind a white dwarf, the core of the original star. Finally, giants into red supergiants, then explode as supernovae, leading to the formation of either a black hole or a neutron star., by MARK GARLICK/SCIENCE PHOTO LIBRARY