Hubble–Reynolds law explained

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

I(R) = (I _{0})/(( 1+ R/R ^{2} _{H)})

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. It was first formulated by Reynolds in 1913^[2] from his observations of galaxies (then still known as nebulae). It was later re-derived by Hubble in 1930^[3] specifically in observations of elliptical galaxies.

Notes and References

1. Binney & Tremaine. Galactic Dynamics 2008.
2. Reynolds . J. H. . The Light Curve of the Andromeda Nebula (N.G.C. 224) . Monthly Notices of the Royal Astronomical Society . 12 December 1913 . 74 . 2 . 132–136 . 10.1093/mnras/74.2.132. 1913MNRAS..74..132R . free .
3. Hubble . E. P. . Distribution of luminosity in elliptical nebulae. . The Astrophysical Journal . May 1930 . 71 . 231 . 10.1086/143250. 1930ApJ....71..231H . free .