Dust Dynamics in Compressible Magnetohydrodynamic Turbulence

By Huirong Yan, A. Lazarian, B. Draine. 2004

134 citations recorded by the source corpus.

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 H2 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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/15f47a30745f8b115d1c313a7d7a8098a376c5c2

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In Astronomy and Astrophysics

1. A. Lazarian
2. A. Tielens
3. E. Jenkins
4. C. Ormel
5. D. Paszun
6. C. Dominik
7. B. Draine
8. C. Gry

Citations in the corpus

• What Is the Total Deuterium Abundance in the Local Galactic Disk? (2006, background): “…timescale for a PAH to collide and coagulate with larger grains is ∼10 Myr in the cold neutral medium, assuming that the larger grains have a total projected area per H nucleon of 10−21 cm2, and a characteristic velocity relative to the gas of ∼ 1 km/s, driven by MHD turbulence (Yan et al. 2004).”
• Tracing Magnetic Fields with Aligned Grains (2007, background): “Plasma-grain interactions seem to be another promising direction, which has been marginally developed so far (see Draine & Lazarian 1998b, Yan et al. 2004, Shukla & Stenflo 2005).”
• Dust coagulation and fragmentation in molecular clouds. I. How collisions between dust aggregates alter the dust size distribution (2009, background): “These expressions only include contributions that arise as a result of the particle’s inertia in a turbulent velocity field and do not contain contributions that arise from gyroresonance acceleration (see, e.g., Yan et al. 2004).”