The acoustic resonant drag instability with a spectrum of grain sizes

ABSTRACT We study the linear growth and non-linear saturation of ‘acoustic Resonant Drag Instability’ (RDI) when dust grains, which drive instability, have a wide, continuous spectrum different sizes. This physics is generally applicable to dusty winds driven by radiation pressure, such as occurs around red-giant stars, star-forming regions, or active galactic nuclei. Depending on physical size grains compared wavelength field that drives wind, two qualitatively regimes emerge. In case are larger than radiation’s – termed constant-drift regime grain’s equilibrium drift velocity through gas approximately independent grain size, leading strong correlations between differently sized persist well into saturated turbulence. For smaller non-constant-drift instability grows more slowly single-grain-size RDI only exhibit RDI-like behaviour in state. A detailed clumping grain–grain collisions shows outflows may be effective sites for collisions, with large collision rates but low velocities.