One of the key background items in this area was the original hypothesis
that most of the matter in the universe was bright. Based on the
assumption that luminosity had a direct relationship with the
amount/distribution of matter in a particular galaxy led to the
conclusion that most of the matter in many galaxies was near the center
of the galaxy. Given that conclusion, an analysis of the rotation at
different distances from the center should yield results similar to those
Kepler found for our own solar system. What was determined was that the
relationship between period and radius did not support the model which
placed most of the matter in a galaxy where most of the luminosity was
(i.e. the center of the galaxy). The conclusion was that the lower
luminosity areas instead of having less mass than the brighter core area
must have some non luminous matter ..... (or the laws of gravity need to
be modified).
Bruce Esser
Physics Teacher Something witty
Marian High School Should go here
Omaha NE http://marian.creighton.edu