Using Globular Clusters to Test Newton?s Law of Gravityy

Abstract

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.

Presented at the IAU220 symposium: "Dark matter in galaxies". Sydney, August 2003