Despite the importance of their size evolution in understanding the dynamical evolution of globular clusters ( GCs ) of the Milky Way , studies are rare that focus specifically on this issue .
Based on the advanced , realistic Fokker–Planck ( FP ) approach , we predict theoretically the initial size distribution ( SD ) of the Galactic GCs along with their initial mass function and radial distribution .
Over one thousand FP calculations in a wide parameter space have pinpointed the best-fit initial conditions for the SD , mass function , and radial distribution .
Our best-fit model shows that the initial SD of the Galactic GCs is of larger dispersion than today ’ s SD , and that typical projected half-light radius of the initial GCs is \sim 4.6 pc , which is 1.8 times larger than that of the present-day GCs ( \sim 2.5 pc ) .
Their large size signifies greater susceptibility to the Galactic tides : the total mass of destroyed GCs reaches 3–5 \times 10 ^ { 8 } ~ { } M _ { \odot } , several times larger than the previous estimates .
Our result challenges a recent view that the Milky Way GCs were born compact on the sub-pc scale , and rather implies that ( 1 ) the initial GCs are generally larger than the typical size of the present-day GCs , ( 2 ) the initially large GCs mostly shrink and/or disrupt as a result of the galactic tides , and ( 3 ) the initially small GCs expand by two-body relaxation , and later shrink by the galactic tides .