Dust-cooling-induced Fragmentation of Low-Metallicity Clouds

We study the dynamical collapse and fragmentation of low-metallicity cloud cores using three-dimensional hydrodynamical calculations, and we devote particular attention to whether or not the cores fragment in the dust-cooling phase. The cores become elongated in the dust-cooling phase because they are unstable to nonspherical perturbation due to the sudden temperature decrease. In the metallicity range of 10^-6 to 10^-5 Z_solar, cores with an initial axis ratio >~2 reach a critical value of the axis ratio (>~30) and fragment into multiple small clumps. This provides a possible mechanism to produce low-mass stars in ultra-metal-poor environments.