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Freeman's law

(Freeman law)
(all spiral galaxy's have the same central surface-brightness)

Freeman's law (i.e., the Freeman law) states that spiral galaxies have the same surface brightness at the center, i.e., within a small range, if any bulge is excluded. The law is not universally accepted: some surveys have supported it, but some observations have not and it has been argued that selection bias produced the apparent fact. A possibility is there exists a population that fits the law and another (e.g., low-surface-brightness galaxies) that does not.


(relation,galaxies,luminosity)
Further reading:
https://en.wikipedia.org/wiki/Freeman_law
https://ui.adsabs.harvard.edu/abs/1970ApJ...160..811F/abstract
http://ned.ipac.caltech.edu/level5/Bothun/Bothun1.html

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