Formation of low-mass condensations in molecular cloud cores via thermal instability

Abstract

The low-mass condensations (LMCs) have been observed within the molecular cloud cores. In this research, we investigate the effect of isobaric thermal instability (TI) applied for forming these LMCs. For this purpose, at first we investigate the occurrence of TI in the molecular clouds. Then, for studying the significance of linear isobaric TI, we use a contracting axisymmetric cylindrical core with axial magnetic field. Consideration to cooling and heating mechanisms in the molecular clouds shows that including the heating due to ambipolar diffusion can lead to the occurrence of TI in a time-scale smaller than dynamical time-scale. Application of linear perturbation analysis shows that isobaric TI can take place in outer region of the molecular cloud cores. Furthermore, the results showthat perturbations with wavelengths greater than few astronomical units are protected from destabilization property of thermal conduction, so they can grow to form LMCs. Thus, the results show that the mechanism of TI can be used to explain the formation of LMCs as the progenitors of collapsing proto-stellar entities, brown dwarfs, or proto-planets.