The ellipticities of Galactic and LMC globular clusters

The correlations between the ellipticity and the age and mass of LMC globular clusters are examined and both are found to be weak. It is concluded that neither of these properties are mainly responsible for the observed differences in the LMC and Galactic globular cluster ellipticity distributions. Most importantly, age cannot be the primary factor in the LMC-Galaxy ellipticity differences, even is there is a relationship, as even the oldest LMC clusters are more elliptical than their Galactic counter-parts. The strength of the tidal field of the parent galaxy is proposed as the dominant factor in determining the ellipticities of that galaxy’s globular clusters. A strong tidal field rapidly destroys velocity anisotropies in initially triaxial, rapidly rotating elliptical globular clusters. A weak tidal field, however, is unable to remove these anisotropies and the clusters remain close to their initial shapes.