# [Physics] Binary Star system with one star stationary

orbital-motionplanetsstars

Can a Binary Star system be possible where in one star is stationary and the other star revolves around it? (Just like a planet revolving a star. i.e planets in the system and the star revolving around their own center of masses to balance the system).

Well, motion is relative so you can choose a frame of reference where one is stationary. If you do though, it makes the equations of motion quite complicated.

Even in our solar system, the Sun isn't stationary. It orbits the center of mass of the whole solar system (barycenter), just as each planet orbits the center of mass.

The center of mass of our solar system moves relative to the sun due to the motion of the Sun and planets. Here is a graph:

(Source)

So you could potentially call a body in a system where the barycenter stays inside that body "stationary" but that's not technically correct, no matter how lopsided the masses of the bodies are. For example:

The larger mass will still always move relative to the system barycenter.