The difference here is that normally when you have something coasting in a circle like that, it's possible to remove energy from the system and have it stop doi

The difference here is that normally when you have something coasting in a circle like that, it's possible to remove energy from the system and have it stop doing that. For example, tidal forces are constantly removing energy from the Earth-Moon system. Here, the theory is that the system is already in its lowest-energy state, despite the fact that part of it is still in motion.