Dynamical Friction on Star Clusters near the Galactic Center

Numerical simulations of the dynamical friction suffered by a star clusternear the Galactic center have been performed with a parallelized tree code.Gerhard (2001) has suggested that dynamical friction, which causes a cluster tolose orbital energy and spiral in towards the galactic center, may explain thepresence of a cluster of very young stars in the central parsec, where starformation might be prohibitively difficult owing to strong tidal forces. Theclusters modeled in our simulations have an initial total mass of 10^5-10^6Msun and initial galactocentric radii of 2.5-30 pc. We have identified a fewsimulations in which dynamical friction indeed brings a cluster to the centralparsec, although this is only possible if the cluster is either very massive(~10^6 Msun), or is formed near the central parsec (<~ 5 pc). In both cases,the cluster should have an initially very dense core (> 10^6 Msun pc-3). Theinitial core collapse and segregation of massive stars into the cluster core,which typically happens on a much shorter time scale than that characterizingthe dynamical inspiral of the cluster toward the Galactic center, can providethe requisite high density. Furthermore, because it is the cluster core whichis most likely to survive the cluster disintegration during its journeyinwards, this can help account for the observed distribution of presumablymassive HeI stars in the central parsec.Comment: Accepted for publication in Ap