If there were no massive objects these things would go flying off, or at least go at a much slower rate because all that determines how they go around is how much mass is inside its orbit.
もしそこに大質量がないとすれば、星は飛び去ってしまうか、 もっとゆっくり周回するでしょう なぜならどう周回するかを決めるのは 軌道内にある質量だからです