Binary

Our solar system has only one star in its centre - the Sun. Binary star system is a star system which has two stars at the centre instead of one.

When a system has two stars, they will rotate around a common centre of mass which is usually somewhere in-between the two stars. This is like two twirling dancers holding hands, although in the case of dancers gravity isn’t involved (usually).

When one of the dancers (or stars) is more massive they will twirl less, while the lighter dancer (or star) will fling out futher out. If they are the same mass, they will rotate roughly around the midpoint.

But why am I even showing you binary stars? Our home star turns out to be unusual - current thinking is that most stars in our galaxy are binaries, trinaries (three stars) or more.