The gravitational force between these two stars provide the required centripetal force for rotation in a circle about their common centre. Assuming 2 mat origin, the centre of mass of the system lies at x=‌
2m×0+m×d
2m+m
=‌
d
3
Hence, FG=FC where, FC is gravitational force between them and FC is centripetal force. ⇒‌‌‌