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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.

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