Gravitational Collapse of Rotating Clouds: Bar and Disk Formation in a Self-Similarly Contracting Cloud

Abstract

Recent observations have revealed that young stars belong to binaries at high frequency as well as the main sequence stars do. Most the binary systems have been formed already in the early phase of the star formation (Mathieu 1994). According to a probable binary formation scenario, a star forming dense cloud fragments during the gravitational collapse phase. The fragments evolve into binary (or multiple stars) after merge and accretion. Many authors have studied fragmentation of collapsing clouds by numerical simulations intensively (reviewed by Bodenheimer, Ruzmaikina, & Mathieu 1993; recent work by Truelove et al. 1998). In those numerical simulations, an almost spherical cloud forms a bar at the center, and the bar fragments to form seeds of binary. The key process is the bar formation in the binary formation. We thus investigate the mechanism and the growth rate of the bar formation by three dimensional numerical simulations.