Turbulence decay and cloud core relaxation in molecular clouds

TL;DR

This paper investigates how the decay of turbulence in molecular clouds influences star formation, introducing the concept of cloud core relaxation as a key phase in the transition from turbulence support to gravitational collapse.

Contribution

It presents a new analysis of turbulence decay effects on star formation, emphasizing the role of cloud core relaxation in the transition to gravitational infall.

Findings

Turbulence decay can enable Jeans' criterion to be met, leading to star formation.

Cloud core relaxation is a critical phase where turbulence diminishes, allowing gravity to dominate.

Decaying turbulence alters the size limits for star-forming cores compared to constant turbulence models.

Abstract

The turbulent motion within molecular clouds is a key factor controlling star formation. Turbulence supports molecular cloud cores from evolving to gravitational collapse and hence sets a lower bound on the size of molecular cloud cores in which star formation can occur. On the other hand, without a continuous external energy source maintaining the turbulence, such as in molecular clouds, the turbulence decays with an energy dissipation time comparable to the dynamic timescale of clouds, which could change the size limits obtained from Jean's criterion by assuming constant turbulence intensities. Here we adopt scaling relations of physical variables in decaying turbulence to analyze its specific effects on the formation of stars. We find that the decay of turbulence provides an additional approach for Jeans' criterion to be achieved, after which gravitational infall governs the motion of the cloud core. This epoch of turbulence decay is defined as cloud core relaxation. The existence of cloud core relaxation provides a more complete understanding in the competition between turbulence and gravity on the dynamics of molecular cloud cores and star formation.