Kinetic Energy Decay Rates of Supersonic and Super-Alfvénic Turbulence in Star-Forming Clouds

TLDR

The study uses 3D isothermal simulations of supersonic, sub‑ and super‑Alfvénic decaying turbulence, comparing different numerical algorithms and performing resolution tests up to 256³ zones or 70³ particles. Kinetic energy in 3D decays as t^−η with 0.85 < η < 1.2, 1D magnetized turbulence decays faster than unmagnetized, and sustaining long lifetimes and supersonic motions requires external driving.

Abstract

We compute 3D models of supersonic, sub-Alfv\'enic, and super-Alfv\'enic decaying turbulence, with an isothermal equation of state appropriate for star-forming interstellar clouds of molecular gas. We find that in 3D the kinetic energy decays as ${t}^{\ensuremath{-}\ensuremath{\eta}}$, with $0.85&lt;\ensuremath{\eta}&lt;1.2$. In 1D magnetized turbulence actually decays faster than unmagnetized turbulence. We compared different algorithms, and performed resolution studies reaching ${256}^{3}$ zones or ${70}^{3}$ particles. External driving must produce the observed long lifetimes and supersonic motions in molecular clouds, as undriven turbulence decays too fast.