According to the law of universal gravitation, any two objects are attracted to each other. the strength of the gravitational force depends on the masses of the objects and their distance from each other.

many stars have planets around them. if there were no gravity attracting a planet to its star, the planet's motion would carry it away from the star. however, when this motion is balanced by the gravitational attraction to the star, the planet orbits the star.

two solar systems each have a planet the same distance from the star. the planets have the same mass, but planet a orbits a more massive star than planet b.