What physical compromise grants stability to a main sequence star?
Hydrostatic equilibrium.
The remarkable stability and consistent energy output observed in main sequence stars, which allows them to shine steadily for billions of years, is maintained by a precise physical state known as hydrostatic equilibrium. This state is a continuous, delicate balance between two immense, opposing forces acting throughout the star's volume. Primarily, there is the overwhelming inward crush exerted by the star's own mass due to gravity. Counteracting this force is the powerful outward push generated by thermal energy released from nuclear fusion in the core, known as radiation pressure. When these inward gravitational forces and outward radiation pressures are perfectly matched at every internal point, the star maintains a constant size and stable luminosity, confirming its main sequence status. This is a self-regulating system; if fusion temporarily dimmed, gravity would cause a slight contraction, increasing core temperature and pressure just enough to reignite the fusion rate.
