Red giant million kelvin) and establishes hydrostatic equilibrium. Over its main sequence life, the star slowly converts the hydrogen in the core into helium; its main-sequence life ends when nearly all the hydrogen in the core has been fused. For the Sun, the main-sequence lifetime is approximately 10 billion years. More-massive stars burn disproportionately faster and so have a shorter lifetime than less massive stars. When the star exhausts the hydrogen fuel in its core, nuclear reactions can no longer continue and so the core begins to contract due to its own gravity. This brings additional hydrogen into a zone where the
Water gas of the carbon dioxide formed when carbon monoxide reacts with water. Water gas Water gas is a mixture of carbon monoxide and hydrogen produced from synthesis gas. Synthesis gas is a useful product, but requires careful handling due to its flammability and the risk of carbon monoxide poisoning. The water-gas shift reaction can be used to reduce the carbon monoxide while producing additional hydrogen, resulting in water gas. Synthesis gas is made by passing steam over a red-hot carbon fuel such as coke: The reaction is endothermic, so the fuel must be continually re-heated to keep the reaction going. In