Stellar structure

Stellar structure is the internal arrangement and physical state of a star, described by how pressure, temperature, density, composition, and energy vary with depth.

Hydrostatic equilibrium: A balance in which pressure gradients counteract gravity in a stable fluid body. This balance sets the pressure gradient that supports a star against its own gravity.
Hydrostatic equilibrium equation: A differential equation balancing the pressure gradient against gravity within a spherical star. It gives the radial pressure profile used in models of stellar interiors.
Standard solar model: A calibrated model of the Sun’s interior structure and evolution. It applies stellar structure equations to the best-measured star.
Radiative zone: A stellar region where energy is transported mainly by radiation. It contrasts with convective regions, where bulk fluid motion carries most of the energy.
Virial theorem: A relation between a system’s average kinetic and potential energies when it is in equilibrium. It links gravitational contraction to the high temperatures inside a star.
Mass continuity equation: A relation describing how enclosed mass changes with radius in a spherical object. It connects a star’s density profile to the mass inside each radius.
Helioseismology: The study of the Sun’s interior using oscillations observed at its surface. Solar oscillations test predicted sound-speed and rotation profiles inside the Sun.
Convection zone: A stellar region where energy is transported mainly by convection. Its nearly adiabatic temperature gradient differs from the steep gradient in radiative regions.
Radiative transfer: The propagation and interaction of radiation with matter. Radiation carries energy through stellar regions where photons diffuse outward.
Energy generation equation: A stellar structure equation relating energy production and transport to changes in luminosity with radius. It tracks where nuclear reactions add energy inside a star.

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