Circular motion of identical spheres in space

[sberreb]

Hey everyone,
I have this question that does not make much sens to me and I can't find any clue on the internet.

Find the shortest possible periode of revolution of two identical gratitating solid spheres which are in circular orbit in free space about a point midway between them. (You can imagine the spheres fabricated from any material obtained by man.)

Some help would be appreciated.
have a good day

 

[Kurdt]

I think Newton's version of Kepler's 3rd law would be appropriate for this problem.