Hubble–Reynolds law

Not to be confused with Hubble's law which relates galaxy redshifts and distances.

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

${\displaystyle I(R)={\frac {I_{0}}{(1+R/R_{H})^{2}}}}$

Where ${\displaystyle I(R)}$ is the surface brightness at radius ${\displaystyle R}$, ${\displaystyle I_{0}}$ is the central brightness, and ${\displaystyle R_{H}}$ 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.

References

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