They move so slowly that a human lifetime is a tiny blip compared to them. This makes their orbit essentially unobservable. But astronomers were able to find the next best thing: the often predicted but never observed stellar stream, or bridge of stars, stretching between the two clouds. A star stream forms when a satellite galaxy feels the gravitational pull of another body. In this case, the gravitational pull of the LMC allowed individual stars to leave the SMC and be pulled toward the LMC. The stars don’t leave at once, they leave individually over time, forming a stream, or...