Hubble–Reynolds law

The Hubble–Reynolds law models the surface brightness of elliptical galaxies as

$I(R) = \frac{I_0}{(1+R/R_H)^2}$

Where $I(R)$ is the surface brightness at radius $R$, $I_0$ is the central brightness, and $R_H$ is the radius at which the surface brightness is diminished by a factor of 1/4. It is asymptotically similar to the De Vaucouleurs' law which is a special case of the Sersic profile for elliptical galaxies.^[1]

The law is named for the astronomers Edwin Hubble and John Henry Reynolds.

References

1. Binney & Tremaine. Galactic Dynamics 2008.