Do tides play a role in the determination of the pre-stellar core mass function?

¹ CRAL, Ecole normale supérieure de Lyon, Université de Lyon, UMR, CNRS 5574, F-69364 Lyon Cedex 07, France
² School of Physics, University of Exeter, Exeter EX4 4QL, UK

^⋆ Corresponding authors; pierre.dumond@ens-lyon.fr; chabrier@ens-lyon.fr

Received: 12 June 2024
Accepted: 20 December 2024

Abstract

Recent studies have examined the role of tides in the star formation process. They suggest, notably, that the tides determine the characteristic mass of the stellar initial mass function (IMF) by preventing the collapse of density fluctuations that would become gravitationally unstable in the absence of the tidal field generated by a neighboring central mass. However, most of these studies consider the tidal collapse condition as a 1D process or use a scalar virial condition and thus neglect the anisotropy of the tidal field and its compressive effects. In the present paper, we consider a turbulence-induced density perturbation formed in the envelope of a central core. This perturbation is subject to a tidal field generated by the central core. We study its evolution taking dynamical effects and the anisotropy of the tides into account. Based on the general tensorial virial equations, we determine a new collapse condition that takes these mechanisms into account. We identify two regimes: (i) a weak tidal regime in which the dynamics of the perturbation is only slightly modified by the action of the tides and (ii) a strong tidal regime in which the density threshold for collapse can potentially be increased due to the combined effects of the tides and the rotational support generated by the tidal synchronization of the perturbation with the orbital motion. In the case of a turbulence-induced density perturbation of mass M_p formed in the vicinity of a first Larson core, which is the case considered in some star formation scenarios, we show that the density threshold above which the perturbation collapses is increased only for low-mass perturbations (M_p ≲ 2.7 M_⊙) and only by at most a factor of 1.5. We conclude that tides likely do not play a major role in the process of star formation or in the determination of the characteristic mass of the IMF. We propose an alternative explanation for the observed value of the characteristic mass of the IMF.