Stellar Interiors & Energy Transport: Physical Mechanisms

Stellar interiors contain a nuclear-burning core and surrounding layers with different temperature, density, ionization, and opacity. Radiative zones carry energy through photon-matter interactions, while convective zones move heat through bulk rising and sinking gas. Some stars also have narrow transition layers and composition gradients created by nuclear burning.

Radiative transport dominates when photons can carry the required flux without producing an excessively steep temperature gradient. When radiative transport becomes inefficient, buoyancy can make hotter material rise and cooler material sink, producing convection. Opacity, ionization state, mass, and composition determine which regime appears.

Helioseismology maps sound-speed structure in the Sun, neutrinos test core reactions, and asteroseismology measures oscillations in other stars. Surface abundances, luminosities, radii, and evolutionary tracks provide additional constraints on interior mixing and transport.

Radiative transport is a random-walk process through repeated matter-radiation interactions. Convection begins when a rising element remains buoyant because the required temperature gradient is too steep for stable radiative transport. Mixing then couples composition evolution to energy transport.