1970 Freeman examined 36 galaxies (type S0-Im) and discovered
all the galaxies had
µ(0) = 21.65 ± 0.30 mag arcsec-2
Appears galaxies are limited in the central surface brightness they can attain
No known physical basis for this limitation
1976 Disney said Freeman's results were due to selection effects
Surveys were then undertaken to find the galaxies previously missed
because of selection effects
Searches over the last 20 years have discovered a huge population of
galaxies well away from the Freeman value
The realization that a large population of galaxies has been missed in
most galaxy studies forces us to rethink old ideas of galaxy formation and
evolution.
