A pair of stars which orbit each other is called a binary star system.
The binary star is a system whereby two stars orbit each other in a common barycentre. With a naked eye, the binary star is distant and seen bright light.
In astrophysics, binary stars are important due to the fact that masses of the stars can be estimated from calculations of their respective orbits. This also allows other stellar measurements such as density and radii to be estimated. They are analysed separately and their orbital period is as long as centuries and millennia.
