Step 4:   Compute the mass of the object at the center of the
               Milky Way (in solar masses).


                   semi-major axis  a  =  (approx)  765    AU


                   Period           P  =  (approx)   16.2  yr


 
                Therefore, the mass of the central object, in solar masses,
                must be

                                 ( 765 AU )^3
                        M   =   ---------------   =  1.7 x 10^(6)  solar masses
                                 ( 16.2 yr )^2