Stellar energy-generation rate ($ϵ$)

The stellar energy-generation rate, $ϵ$, is power supplied per unit mass, conventionally measured in $\mathrm{W}\mathrm{k}{\mathrm{g}}^{-1}$. In a stationary spherical model with specified local net sources,Here $L_r$ is the luminosity crossing a sphere and $dm=4\pi r^2\rho dr$ is its shell mass. A localized source therefore increases the outward luminosity across that shell.

The convention must say whether $ϵ$ includes losses such as stellar neutrino energy loss. During stellar evolution, changing internal energy and contraction add terms to the full energy equation. A high nuclear reaction rate does not necessarily equal immediately escaping surface light: energy must still be transported through the stellar structure.