Gebhardt has data in hand from a ground-based survey of star motions in about 15 other Milky Way clusters, most of them easier to study than the crowded heart of M15.

• 吉布哈特手中有地面观测的其他15个球状星团中恒星运动的数据资料，其中大部分的核心没有M15那么稠密。