The mass density of a spherical galaxy varies as $K\over r$ over a large distance 'r' from its center. In that region, a small star is in a circular orbit of radius R. Then the period of revolution, T depends on R as :

(1) $T^2\propto{1\over R^3}$

(2) $T^2\propto R$

(3) $T\propto R$

(4) $T^2\propto R^3$

(1) $T^2\propto{1\over R^3}$

(2) $T^2\propto R$

(3) $T\propto R$

(4) $T^2\propto R^3$