The Intermittent Dissipation of Turbulence: is it Observed in the Interstellar Medium?

Summary

The viscous dissipation process in supersonic flows is known to be highly intermittent in space and time. It means that the volume over which the turbulent energy is released is as small as the character of intermittency is pronounced. In the interstellar medium, this phenomenon is predicted to induce large fluctuations at small scales of the gas properties. Since the interstellar viscous dissipation scale is out of reach of current observational capabilities, indirect signatures of the presence of this process in the interstellar medium would be valuable. A few possible indirect signatures are presented here.

Introduction

On average in our Galaxy, about 10⁻³ L_⊙/M_⊙ are permanently driven into heat due to the viscous dissipation of supersonic turbulence. On average again, this is negligible compared to the heating due to the UV stellar radiation which is about 1 L_⊙/M_⊙. But it is now known that a large fraction of the energy released by the dissipation of turbulence is not distributed evenly but is concentrated in localized regions of space and time because most of the dissipation occurs in bursts. This phenomenon is known as the intermittency of turbulent dissipation. In those regions of interstellar space where viscous dissipation occurs, the corresponding heating term becomes temporarily dominant, even in regions poorly shielded from the ambient interstellar radiation field. This significantly modifies the subsequent evolution of the gas which has received this energy, in comparison to that of gas of its neighborhood which has not received it.