Answer:
the force will increase by a factor 2.25
Step-by-step explanation:
The gravitational force between the two stars is given by:

where
G is the gravitational constant
m1, m2 are the masses of the two stars
r is the distance between the stars
If the distance is decreased by one-third, it means that the new distance is 2/3 of the previous distance

So the new force will be

So, the force will be 2.25 times the previous value.