Small-scale clustering of nano-dust grains in supersonic turbulence

TL;DR

This paper demonstrates that nano-sized dust grains can cluster in turbulent flows, significantly increasing local density and potentially influencing astrophysical phenomena like ultraviolet extinction.

Contribution

It provides the first high-resolution simulation evidence of nano-dust clustering in supersonic turbulence, highlighting its potential impact on dust aggregation and extinction properties.

Findings

Nano-dust grains cluster in turbulent flows, increasing local density.

Clustering may enhance dust aggregation probabilities.

Model explains extreme ultraviolet extinction in GRB host.

Abstract

We investigate the clustering and dynamics of nano-sized particles (nano-dust) in high-resolution ($1024^3$) simulations of compressible isothermal hydrodynamic turbulence. It is well-established that large grains will decouple from a turbulent gas flow, while small grains will tend to trace the motion of the gas. We demonstrate that nano-sized grains may cluster in a turbulent flow (fractal small-scale clustering), which increases the local grain density by at least a factor of a few. In combination with the fact that nano-dust grains may be abundant in general, and the increased interaction rate due to turbulent motions, aggregation involving nano dust may have a rather high probability. Small-scale clustering will also affect extinction properties. As an example we present an extinction model based on silicates, graphite and metallic iron, assuming strong clustering of grain sizes in the nanometre range, could explain the extreme and rapidly varying ultraviolet extinction in the host of GRB 140506A.