In contrast, gravitationally bound objects follow elliptic orbits around the Sun. More slowly rotating asteroids are sometimes gravitationally bound aggregates. The Moon gravitationally perturbs 's geocentric orbit, causing it to be unstable. A gravitationally lensed galaxy also provides indirect evidence of Population III stars. It may be a gravitationally bound companion of the Andromeda Galaxy. M82 is a galaxy that is interacting gravitationally with M81. A multi-star system consists of two or more gravitationally bound stars that orbit each other. Like most open clusters, the Pleiades will not stay gravitationally bound forever. Objects that are gravitationally bound will rotate around a common center of mass. Common in space are binary systems, two objects gravitationally coupled to each other. However, it has yet to be demonstrated conclusively that they are gravitationally bound. A sphere is the only stable shape for a non-rotating, gravitationally self-attracting liquid. Titan is the sixth gravitationally rounded moon from Saturn. It can be shown that such bodies are gravitationally equivalent to point sources.