An equation for stellar structure which arises in a model based on the assumption that the star is a gaseous sphere in adiabatic equilibrium, in which the pressure is proportional to ργ, where ρ is the density and γ is a constant; the equation is d²y/dx² + (2/x )dy/dx + yⁿ=0, where n =1/(γ-1), x is proportional to the distance from the center of the sphere, and y is proportional to ρ^1/n. Also known as Lane-Emden equation.