Most galaxies are fit by Sérsic profiles with indices in the range 1/2 < n < 10. The best-fit value of n correlates with galaxy size and luminosity, such that bigger and brighter galaxies tend to be fit with larger n. Setting n = 4 gives the de Vaucouleurs profile : I ( R ) ∝ ∝ e − − b R 1 / 4 which is a rough approximation of ordinary elliptical galaxies. Setting n = 1 gives the exponential profile: I ( R ) ∝ ∝ e − − b R which is a good approximation of spiral galaxy disks and a rough approximation of dwarf elliptical galaxies. The correlation of Sérsic index (i.e. galaxy concentration) with galaxy morphology is sometimes used in automated schemes to determine the Hubble type of distant galaxies. Sérsic indices have also been shown to correlate with the mass of the supermassive black hole at the centers of the galaxies.