Collapse and Fragmentation of Molecular Cloud Cores. III. Initial Differential Rotation

Details Collapse and Fragmentation of Molecular Cloud Cores. III. Initial Differential Rotation Collapse and Fragmentation of Molecular Cloud Cores. III. Initial Differential Rotation

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...451..218b&link_type=abstract

Astrophysical Journal v.451, p.218

Astronomy and Astrophysics

Astronomy

35

Hydrodynamics, Ism: Clouds, Ism: Kinematics And Dynamics, Ism: Molecules, Stars: Binaries: General, Stars: Formation

Scientific paper

Fragmentation during protostellar collapse is the leading mechanism for explaining the formation of binary and multiple stars. Most calculations of protostellar fragmentation have assumed the initial molecular cloud cores to be in solid body rotation, whereas differential rotation might characterize some molecular cloud cores. Here we use a second-order accurate, radiative hydrodynamics code to calculate the self-gravitational collapse of three-dimensional protostellar clouds, starting from centrally condensed (Gaussian), prolate (1.5:1 and 2:1 ratios) configurations, with varying degrees of differential rotation. The initial differential rotation is characterized by an exponent γι specifying the dependence of the initial angular velocity profile on the initial density (Ωι ∝ ργιι); γι = 0 produces initially solid body rotation, while γι = ⅔ results in the maximum degree of differential rotation consistent with spherical contraction at conserved mass and angular momentum. Depending on the value of γι, and the initial ratios of thermal (αι) and rotational (βι) to gravitational energy, three types of outcomes result: slow contraction, vigorous collapse without fragmentation, or collapse leading to fragmentation. Fragmentation occurs for γι = ⅔ clouds with initial 1.5:1 axis ratios when αι < 0.45 and βι ≍ 0.1, whereas γι = 0 clouds only fragment for αι < 0.3. For initial 2:1 axis ratios, fragmentation requires αι < 0.5 and βι ≍ 0.1 for γι = ⅔, compared to αι < 0.4 for clouds with γι = 0. These criteria quantify the extent to which initial differential rotation enhances rotationally driven fragmentation by concentrating the angular momentum per unit mass in the densest regions of the cloud. Gaussian clouds in rapid differential rotation can fragment even if they start collapse from a configuration close to virial equilibrium (αι + βι = ½).

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