“While a star is on the main sequence, it makes only helium. A star leaves the main sequence when it exhausts the supply of available hydrogen in its core. The post-main sequence fate of the star, and the range of elements produced, depends on the mass of the star. The lowest mass M stars, roughly below .2 Solar masses, are well mixed and can always bring hydrogen from outer layers to the core to sustain fusion. Such stars become gradually more luminous over trillions of years as they convert their hydrogen into helium, until they exhaust their fuel and fade away as white dwarf stars. White dwarf stars are no longer producing energy by fusion. Because of contraction, their surface temperatures are high (hence their bluish-white colour), but they have low luminosity because they are very small. White dwarfs are a common form of stellar remnant. All white dwarfs eventually cool down and go dark, but this process takes many times the current age of the Universe.” Stellar EvolutionWhite DwarfMain Sequence Book:Planetary Systems: A Very Short Introduction Source: Planetary Systems: A Very Short Introduction