2013MNRAS.430..961K

Our purpose in this paper is to explore the thermal effects on the dynamical evolution of a spherical low-mass core at the very beginning of the collapse process. Thus, we have investigated the perturbation theory in order to study the early core evolution and we have ignored the magnetic field, ambipolar diffusion and dust effects. We show how a non-isothermal marginally stable low-mass starless core experiences contraction. With this aim in mind, we consider the bulk oscillations of a self-gravitating starless core on the verge of gravitational instability under the influences of cosmic ray heating and gas cooling rates that have a complicated dependence on the temperature and density of molecular and atomic abundances. We conclude that the equilibrium state is described by a polytropic equation of state. Moreover, with our supposed simplification, the first-order and second-order perturbed pressures are also described by polytropic equations of states. We conclude that, although the disturbances in our core model travel with different speeds for different values of the polytropic index, the core faces a subsonic, accelerating collapse.