An isolated triple star system consists of two identical stars, each of mass m and a fixed star of mass M. They revolve around the central star in the same circular orbit of radius r. The two orbiting stars are always at opposite ends of a diameter of the orbit. The time period of revolution of each star around the fixed star is equal to :

(1) $\frac{4{\mathrm{\pi r}}^{\frac{3}{2}}}{\sqrt{\mathrm{G}\left(4\mathrm{M}+\mathrm{m}\right)}}$
(2) $\frac{2{\mathrm{\pi r}}^{\frac{3}{2}}}{\sqrt{\mathrm{GM}}}$
(3) $\frac{2{\mathrm{\pi r}}^{\frac{3}{2}}}{\sqrt{\mathrm{G}\left(\mathrm{M}+\mathrm{m}\right)}}$
(4) $\frac{4{\mathrm{\pi r}}^{\frac{3}{2}}}{\sqrt{\mathrm{G}\left(\mathrm{M}+\mathrm{m}\right)}}$