Hydrostatic Equilibrium

As we have noted earlier in discussing energy production and energy transport in stars, the exquisite balance between pressure trying to expand a star and gravity trying to contract it is called hydrostatic equilibrium.

The stable stages of a star's life correspond to times of hydrostatic equilibrium. The less stable stages, when the star is expanding or contracting, correspond to departures from hydrostatic equilibrium. This animation illustrates the concept of hydrostatic equilibrium in a star.