  The presence of dark matter, though well established by indirect evidence, is
yet to be observed directly. Various dark matter detection experiments running
for several years have yielded no positive results. In view of these negative
results, we had earlier proposed alternate models by postulating a minimum
gravitational field strength (minimum curvature) and a minimum acceleration.
These postulates led to the modified Newtonian dynamics and modified Newtonian
gravity (MONG). The observed flat rotation curves of galaxies were also
accounted for through these postulates. Here we extend these postulates to
galaxy clusters and model the dynamical velocity-distance curve for a typical
cluster such as the Virgo cluster. The radial velocities of galaxies in the
Virgo cluster are also obtained through this model. Observations show an
inconsistency in the Hubble flow at a mean cluster distance of 17 Mpc, which is
expected in regions of high matter density. This decrease in velocity is
predicted by our model of modified gravity (MONG). The radial velocity versus
distance relation for galaxies in the Virgo cluster obtained using MONG is in
agreement with observations.
