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(circle dot), cores with an initial axis ratio greater than or similar to 2 reach a critical value of the axis ratio ( greater than or similar to 30) and fragment into multiple small clumps. This provides a possible mechanism to produce low-mass stars in ultra-metal-poor environments.