How Many Young Star Clusters Exist in the Galactic Center? .

We study the evolution and observability of young compact star clusters within about 200 pc of the Galactic center. Calculations are performed using direct N-body integration on the GRAPE-4, including the effects of both stellar and binary evolution and the external influence of the Galaxy. The results of these detailed calculations are used to calibrate a simplified model applicable over a wider range of cluster initial conditions. % We find that clusters within 200 pc from the Galactic center dissolve within 70 Myr. However, their projected densities drop below the background density in the direction of the Galactic center within about 20 Myr, effectively making these clusters undetectable after that time. Clusters farther from the Galactic center but at the same projected distance are more strongly affected by this selection effect, and may go undetected for their entire lifetimes.
Based on these findings, we conclude that the region within 200 pc of the Galactic center could easily harbor some 50 clusters with properties similar to those of the Arches or the Quintuplet systems.
For details see Portegies Zwart, S.F., Makino, J., McMillan, S.L.W., Hut, P., 2001, ApJ 546, L101
The lives and deaths of star clusters near the Galactic center

We study the evolution and observability of young, compact star clusters near the Galactic center, such as the Arches and Quintuplet systems. The clusters are modeled by integrating the equations of motion of all stars while accounting for the internal evolution of the stars and binaries and the effect of the tidal field of the Galaxy. We find that clusters within 150pc of the Galactic center dissolve within ~55 Myr, but their projected densities drop below the background density in the direction of the Galactic center within only a few Myr, effectively making these clusters undetectable after that time. Detailed observations of the Arches cluster, when taken at face value, suggest that its mass function is unusually flat and that the cluster contains an overabundance of stars more massive than 20Msun. Our dynamical analysis, however, shows that the observed characteristics of the Arches cluster are consistent with a perfectly normal initial mass function. The observed anomalies are caused by a combination of observational selection effects and the dynamical evolution of the cluster. We calibrate the current parameters of the Arches cluster using a normal initial mass function and conclude that the cluster is more massive than 40000Msun has a half mass radius of about 0.35pc, and is located between 50 and 90pc from the Galactic center.
For details see Portegies Zwart, S.F., Makino, J., McMillan, S.L.W., Hut, P., 2001, submitted to ApJ (astro-ph/0102259)

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