  The rotation dynamics of spiral galaxies is modeled using a sum of two mass
distributions: a spherical bulge and a thin disk. The density functions
representing these mass distributions are calculated from the total angular
momentum of the galaxy and known rotation curves. When both bulge and disk
density functions are assumed to be smooth and are given a value of zero beyond
the edge of the galaxy, a unique solution is obtained. Moreover, the calculated
density functions show that constant rotation curves are obtained from a nearly
exponential luminosity profile with a dark matter distribution which follows
that of the light emitting matter, without the need for modified Newtonian
dynamics. Experimental detection of molecular hydrogen in spiral galaxies
confirms the presence of a baryonic massive component consistent with the
results obtained with this model. It is proposed that dark matter does not have
to be exotic non-baryonic matter. Instead, it can be made of molecular hydrogen
and condensed matter.
