Hydrostatic Equilibrium

Balance between gravityAttractive force between all matter - one of the four fundamental forces. and gas pressure. In the case of a starSelf-luminous object held together by its own self-gravity. Often refers to those objects which generate energy from nuclear reactions occurring at their cores, but may also be applied to stellar remnants such as neutron stars., gravity originates in mutual gravitational attraction of the entire mass of the star. Gas pressure is produced by nuclear reactions that heat the star’s gas. Any change in the internal temperature of a star results in a change in its diameter: if a star cools, it will contract; if it grows hotter, it will expand. The same concepts apply to the gaseous atmospheres of planets.