Freeman Law

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.

The Freeman law was confirmed in year 2010 for a sample of 30000 Sloan Digital Sky Survey galaxy images 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.

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