  New measurements of the velocity dispersion of the globular cluster omega
Centauri allow to trace its gravitational potential down to an acceleration of
8e-9 cm/s/s. It is found that the dispersion profile remains flat well inside
the tidal radius as soon as the acceleration of gravity approaches a_0, a
result that finds its simplest explanation within the contest of Modified
Newtonian dynamics. A similar behavior is observed in the globular cluster M15
showing this is not a peculiar features of omega Centauri. This result is
surprising and suggestive of a failure of Newton's law at low accelerations.
