  Spiral galaxies are considered as static, spherically symmetric Dark Matter
Configurations (DMC)in which non-zero rest-mass particles (NZRPs) move along
appropriate trajectories. Using general relativity (GR), we show that a mass of
dark matter about 127 - 212 $\times 10^{11} M_{\odot}$ is required inside the
sphere of size $a \sim 10 $ kpc for agreement with the observed typical orbital
velocity ranging from 150 to 250 km sec$^{-1}$. In our model, it is possible to
obtain flat, slightly rising, and even declining rotation curves. The model
self-evidently explains the reason why most of the spirals show almost flat or
slightly rising rotation curves and very few show declining curves. The NZRPs
follow trajectories, and are finally trapped in circles of minimum radii $\sim
0.03a - 0.005a$ with rotation velocities reaching $\sim 6544-8445$ km sec
$^{-1}$. The velocity values are consistent with observations of central
regions of various galaxies. This scenario may also lead to conditions suitable
for evolution of relativistic supermassive stars and supermassive black holes
at the centres of various galaxies. Based on this study, we obtain the density
parameter $\Omega \sim 0.127 - 0.212 $, leading to an open model of the
Universe with an age of $\sim 16.8 - 17.6 $ Gyr, which is significantly higher
than the presently estimated age of globular clusters $\sim 13 - 15 $ Gyr.
