Multiple star systems. Most stars in the universe are NOT alone. Stars more often than not come in pairs, or in threes, fours, or even sixes. Two star systems are called binary star systems. Yes, some stars belong to gravitationally bound systems that contain more than one star. These stars therefore rotate around each other. Our star, the Sun, is an exception. We have only one star in our solar system. We will talk about some of these multiple star systems in this show.