Effects of Hardness of Primordial Binaries on the Evolution of Star Clusters

We have investigated the effects of the hardness of primordial binaries on the whole evolution of star clusters by means of N-body simulations. Using a newly developed code, GORILLA, we simulated eleven N = 16384 clusters with primordial binaries whose binding energies are equal in each cluster in the range of 1-300 kT(0), where 1.5 kT(0) is the average stellar kinetic energy at the initial time. We found that, in both the soft (<= 3 kT(0)) and hard (>= 300 kT(0)) limits, clusters experience deep core collapse. For intermediate hardness (10-100 kT(0)), the core collapses halt halfway due to an energy releases of the primordial binaries. The core radii at the halt can be explained by their energy budget.