Freeman law

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The Freeman law is a statement in astronomy which says that disk galaxies have the same surface brightness, Σ at the center. It was described in 1970 by Ken Freeman.[1][2]

The Freeman law was confirmed in year 2010 for a sample of 30000 Sloan Digital Sky Survey galaxy images [3] and it can be used with the Tully-Fisher relation to determine the luminosity and therefore distance of an observed galaxy.

However more recently it has been argued that the Freeman law is an effect of selection bias.[1][4] The Freeman law is sometimes called the Fish-Freeman effect.[5]

Fish law

The Fish law (or Fish's law) in astronomy is the analogue for the Freeman law with disk galaxies replaced by elliptical galaxies. It was described in 1964 by Robert A. Fish based on photometric results for 29 elliptical galaxies.[6]

Modified Newtonian Dynamics (MOND)

According to Brada and Milgrom,[7]

The acceleration constant of the modified dynamics (MOND), a0, appears in various predicted regularities pertinent to galaxies. For example, it features as an upper cutoff to the mean surface density (or mean surface brightness translated with M/L) of galaxies, as observed and formulated in the Freeman law for disks, and of the Fish law for ellipticals.


  1. ^ a b McGaugh, S. S; Bothun, G. D; Schombert, J. M (1995). "Galaxy Selection and the Surface Brightness Distribution". The Astronomical Journal. 110 (1995): 573. arXiv:astro-ph/9505062. Bibcode:1995AJ....110..573M. doi:10.1086/117543.
  2. ^ Freeman, Kenneth C. (1970). "On the disks of spiral and S0 galaxies". The Astrophysical Journal. 160 (3): 811–830. Bibcode:1970ApJ...160..811F. doi:10.1086/150474.
  3. ^ Fathi, Kambiz (2010). "Revisiting the Scale Length-mu0 Plane and the Freeman Law in the Local Universe". The Astrophysical Journal. 722: L120. arXiv:1009.2692. Bibcode:2010ApJ...722L.120F. doi:10.1088/2041-8205/722/1/L120.
  4. ^ Minnesota State University, ""Archived copy". Archived from the original on 2007-07-06. Retrieved 2008-01-11.CS1 maint: Archived copy as title (link)"
  5. ^ Disney, M.; Phillipps, S. (1983). "The visibility of galaxies as a function of central surface brightness". Monthly Notices of the Royal Astronomical Society. 205 (4): 1253–1265. Bibcode:1983MNRAS.205.1253D. doi:10.1093/mnras/205.4.1253.
  6. ^ Fish, Robert A. (1964). "A Mass-Potential Relationship in Elliptical Galaxies and Some Inferences Concerning the Formation and Evolution of Galaxies". The Astrophysical Journal. 139 (1): 284–305. Bibcode:1964ApJ...139..284F. doi:10.1086/147753.
  7. ^ Brada, Rafael; Milgrom, Mordehai (December 1998). "The modified dynamics (MOND) predicts an absolute maximum to the acceleration produced by 'dark halos'". The Astrophysical Journal. 512 (17): L17. arXiv:astro-ph/9812117. Bibcode:1999ApJ...512L..17B. doi:10.1086/311871.

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