A Production Mechanism for Clusters of Dense Cores

Collapse and fragmentation processes within filamentary interstellar molecular clouds are investigated in detail. A quasi-equilibrium filament fragments into dense cores separated by about 4 times the filament diameter. Nonlinear calculations reveal that the central region of each core tends toward spherical collapse and further hierarchical fragmentation is not expected. However, merging and clustering of cores tend to occur soon after the fragmentation. When the line mass of an isothermal filament exceeds the critical value for equilibrium by a small amount, perturbations do not grow much, and the entire filament collapses toward the axis without fragmenting. In this case no characteristic scale for fragmentation appears during the isothermal collapse phase. Subsequent evolution is also investigated. A change of the equation of state yields a characteristic density, separation length, and mass for fragmentation. These values correspond to 5 × 10^-15 g cm^-3, 2 × 10^-3 pc, and 4 × 10^-2 M_☉, if the cloud temperature is 10 K. These results are consistent with recent high-resolution radio observations of dense cores in Taurus dark cloud.