Turbulence decay and cloud core relaxation in molecular clouds

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.

18 pages, 1 figure, accepted for publication in ApJ

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• Observational signatures of cosmic ray interactions in molecular clouds
• Inverse energy transfer in decaying, three dimensional, nonhelical magnetic turbulence due to magnetic reconnection
• Studies of Turbulence Dissipation in Taurus Molecular Cloud with Core Velocity Dispersion (CVD)
• The X-ray Decay of the ultraluminous supernova SN 1978K in NGC 1313
• Recurrent outbursts revealed in 3XMM J031820.8-663034
• Thermal instability through the outer half of quasi-static spherically symmetric molecular clumps and cores
• Collapsing Index: A New Method to Identify Star-forming Cores Based on ALMA Images