Bar and Disk Formation in Gravitationally Collapsing Clouds: Implications for Binary Formation

Details Bar and Disk Formation in Gravitationally Collapsing Clouds: Implications for Binary Formation Bar and Disk Formation in Gravitationally Collapsing Clouds: Implications for Binary Formation

Aug 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...521..659m&link_type=abstract

The Astrophysical Journal, Volume 521, Issue 2, pp. 659-670.

Astronomy and Astrophysics

Astronomy

17

Stars: Binaries: General, Hydrodynamics, Instabilities, Ism: Clouds, Stars: Formation

Scientific paper

We investigated the dynamical collapse of a molecular cloud core with three-dimensional numerical simulations. Our simulations show that an initially spherical core produces a bar or disk during its dynamical collapse. The disk and bar formation is due to instability. Velocity perturbations grow in proportion to rho^1/6_c, where rho_c denotes the central density. The growing velocity perturbations are due to two effects, rotation and shear. Rotation makes the core spin faster to produce a disk at the center. On the other hand, velocity shear elongates or shortens the core in one direction to form a bar or nonrotating disk. When the core rotates nonuniformly, the collapse produces a disk containing a bar at its center by the growth of rotation and shear. This bar is much longer than the Jeans length and is likely to be unstable against fragmentation. We expect that the bar will evolve into a binary or multiple stars. The binary or multiple stars will be surrounded by a common disk. We also demonstrate the growth of an eigenmode that leads to bar and disk formation. On the basis of our numerical simulations, we give a condition for formation of a disk and bar during the isothermal collapse phase of a molecular cloud core. If the core has an oblateness of 10% or an equivalent velocity shear at n_H_2~=10^4 cm^-3, the core produces a bar by the end of its isothermal collapse phase.

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