Dynamical collapse and fragmentation of low-metallicity cloud cores is studied using three-dimensional hydrodynamical calculations , with particular attention devoted whether the cores fragment in the dust-cooling phase or not .
The cores become elongated in this phase , being unstable to non-spherical perturbation due to the sudden temperature decrease .
In the metallicity range of 10 ^ { -6 } -10 ^ { -5 } Z _ { \odot } , cores with an initial axis ratio \gtrsim 2 reach a critical value of the axis ratio ( \gtrsim 30 ) and fragment into multiple small clumps .
This provides a possible mechanism to produce low-mass stars in ultra-metal-poor environments .