de Vaucouleurs's law

An empirical galaxy surface-brightness profile in which the logarithm of intensity varies with the fourth root of projected radius. It is the Sérsic profile with index four.

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Sérsic profile: A family of projected surface-brightness profiles whose shape is controlled by an index. The law is the special case of this family with index four.
Gérard de Vaucouleurs: A French astronomer known for research on galaxy structure and classification. He established the empirical profile through studies of elliptical galaxies.
Bulge-disk decomposition: A method that separates a galaxy’s image into central bulge and extended disk components. The law often models the bulge component in this decomposition.
Exponential profile: A surface-brightness profile whose intensity declines exponentially with radius. It commonly describes galaxy disks, unlike the law’s centrally concentrated profile.
Effective radius: The projected radius enclosing half a system’s total luminosity. It sets the characteristic scale of the profile.
Elliptical galaxy: A galaxy with a smooth, ellipsoidal stellar distribution and little organized structure. The profile was developed to describe the light of these galaxies.
Galaxy formation and evolution: The processes that build galaxies and change their properties over cosmic time. Profile shape and scale help compare galaxy structures across populations and epochs.
Gaussian profile: A profile whose intensity declines as the exponential of squared distance from its center. Its rapid outer decline differs from the law’s extended wings.
Central surface brightness: The surface brightness at the center of a resolved astronomical object. It helps set the profile’s brightness normalization.
Galaxy morphology: The classification and description of galaxies by their visible structure and shape. The law grew from efforts to quantify galaxy structure.