Galactic mapping with general relativity and the observed rotation
  curves
  Typically, stars in galaxies have higher velocities than predicted by
Newtonian gravity in conjunction with observable galactic matter. To account
for the phenomenon, some researchers modified Newtonian gravitation; others
introduced dark matter in the context of Newtonian gravity. We employed general
relativity successfully to describe the galactic velocity profiles of four
galaxies: NGC 2403, NGC 2903, NGC 5055 and the Milky Way. Here we map the
density contours of the galaxies, achieving good concordance with observational
data. In our Solar neighbourhood, we found a mass density and density fall-off
fitting observational data satisfactorily. From our GR results, using the
threshold density related to the observed optical zone of a galaxy, we had
found that the Milky Way was indicated to be considerably larger than had been
believed to be the case. To our knowledge, this was the only such existing
theoretical prediction ever presented. Very recent observational results by Xu
et al. have confirmed our prediction. As in our previous studies, galactic
masses are consistently seen to be higher than the baryonic mass determined
from observations but still notably lower than those deduced from the
approaches relying upon dark matter in a Newtonian context. In this work, we
calculate the non-luminous fraction of matter for our sample of galaxies that
is derived from applying general relativity to the dynamics of the galaxies.
The evidence points to general relativity playing a key role in the explanation
of the stars' high velocities in galaxies. Mapping galactic density contours
directly from the dynamics opens a new window for predicting galactic
structure.
