The results of N -body simulations of the effects of the expulsion of residual gas ( that gas not used in star formation ) from very young globular clusters is presented .
Globular clusters of a variety of initial masses , Galactocentric radii , concentration and initial mass function slope with star formation efficiencies of \lower 2.58 pt \hbox { $ \buildrel < \over { \sim } $ } 50 \% were simulated .
The residual gas was expelled by the action of massive stars in one of three idealised ways : gradually by their UV flux and stellar winds ; gradually by the input of energy by supernovae ; and in a ’ supershell ’ expanding from the cluster centre .
The clusters were compared shortly after the gas expulsion with the results of Chernoff & Shapiro ( 1987 ) to estimate whether they would survive for a Hubble time .
It is found that the expulsion of \lower 2.58 pt \hbox { $ \buildrel > \over { \sim } $ } 50 \% of a globular clusters mass in a short period of time considerably affects the structure of the cluster .
However , many clusters are estimated to be able to survive with reasonable initial conditions , even if their star formation efficiencies are possibly as low as 20 % .
It is found that the central density required within a proto-globular cluster at star formation in order for it to survive at a given Galactocentric radius is independent of the mass of stars in the cluster .
For globular clusters in the inner few kpc of the Galaxy this value is found to be around 10 ^ { 3 } M _ { \odot } pc ^ { -3 } , falling as Galactocentric radius increases .
This value is similar to the central densities found in giant molecular clouds in the Galaxy today .
It is suggested that a globular cluster could reasonably form with that central density with a star formation efficiency of \approx 40 \% and and initial mass function slope \alpha \approx 3 .