Bondi-Hoyle Accretion in Dense Star Clusters: Implications for Stars, Disks, and Planets Draft version: May 22, 2007

We investigate the Bondi-Hoyle accretion of gas from a GMC onto young stardisk systems in a cluster. This post-formation accretionary phase can continue for several Myr after young stars are born, until the gas is heated by massive stars and removed from the cluster, or when low-mass stars are ejected from the cluster. We perform N-body simulations of stars orbiting in young model clusters using 30, 500, and 3000 stars. We include the gravitational effects of stars and gas. The average mass accretion rate for a star dM/dt is proportional to M, consistent with observations of accretion in young stars. For solar mass stars, the accretion rate is approximately 5 × 10 M⊙, and the total mass accreted is 0.05 M⊙. The 1σ spread in accretion rates for stars of the same mass varies by a factor of 500, due to variations in stars’s position and velocity. The mass accreted is insignificant compared to the star’s mass, but it is comparable to or greater than the disk mass. The accretion flow is likely to pass through the disk, where it may significantly affect the planetesimal and planet-formation process, by increasing the amount of raw material available, and providing it over several Myr. We discuss a variety of implications of this process, including its effect on the formation of terrestrial and gas-giant planets, the migration of extrasolar planets, FU Ori outbursts, and metallicity variations between a star and its planets.