Surface Gravity Star

The surface gravity of a star, expressed as log g, is a fundamental parameter that influences the shape of spectral lines and therefore the classification of stars. A higher log g indicates a more compact, denser star, while a lower value points to a larger, more diffuse object such as a giant or supergiant.

Surface gravity is directly linked to a star’s mass (M) and radius (R) through Newton’s law of gravitation. In cgs units the acceleration at the stellar surface is g = GM/R², where G is the gravitational constant. Because astronomers often work with orders of magnitude, the logarithmic form log g = log₁₀(GM/R²) is used.

Accurate log g values are essential for modelling stellar atmospheres, determining evolutionary status, and estimating distances via spectroscopic parallax. By measuring a star’s mass and radius—often obtained from binary dynamics or asteroseismology—one can compute its surface gravity and place it correctly on the Hertzsprung‑Russell diagram.