Dust dynamics in compressible magnetohydrodynamic turbulence

Huirong Yan, A. Lazarian, B. T. Draine

Research output: Contribution to journalArticlepeer-review

129 Scopus citations


We calculate the relative grain-grain motions arising from interstellar magnetohydrodynamic (MHD) turbulence. The MHD turbulence includes both fluid motions and magnetic fluctuations. While the fluid motions accelerate grains through hydrodrag, the electromagnetic fluctuations accelerate grains through resonant interactions. We consider both incompressive (Alfvén) and compressive (fast and slow) MHD modes and use descriptions of MHD turbulence obtained by Cho and Lazarian in 2002. Calculations of grain relative motion are made for realistic grain charging and interstellar turbulence that are consistent with the velocity dispersions observed in diffuse gas, including cutoff of the turbulence from various damping processes. We show that fast modes dominate grain acceleration and can drive grains to supersonic velocities. Grains are also scattered by gyroresonance interactions, but the scattering is less important than acceleration for grains moving with sub-Alfvénic velocities. Since the grains are preferentially accelerated with large pitch angles, the supersonic grains will be aligned with long axes perpendicular to the magnetic field. We compare grain velocities arising from MHD turbulence with those arising from photoelectric emission, radiation pressure, and H 2 thrust. We show that for typical interstellar conditions, turbulence should prevent these mechanisms from segregating small and large grains. Finally, gyroresonant acceleration is bound to preaccelerate grains that are further accelerated in shocks. Grain-grain collisions in the shock may then contribute to the overabundance of refractory elements in the composition of Galactic cosmic rays.

Original languageEnglish (US)
Pages (from-to)895-911
Number of pages17
JournalAstrophysical Journal
Issue number2 I
StatePublished - Dec 1 2004

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Dust, extinction
  • ISM: Kinematics and dynamics
  • ISM: magnetic fields
  • MHD
  • Turbulence


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