Charging of Aggregate Grains in Astrophysical Environments

TL;DR

This paper investigates how irregularly-shaped aggregate dust grains in space acquire electric charge, considering various emission processes, and finds that their charge differs significantly from spherical grains, affecting their dynamics.

Contribution

It introduces a comprehensive model for charging irregular aggregate grains, including secondary electron emission and photoemission, highlighting the impact of structure on charge estimation.

Findings

Aggregate charge can differ markedly from spherical grains of the same mass.

Structural characteristics enable charge estimation in specific environments.

Secondary electron emission significantly influences micron-sized aggregate charging.

Abstract

The charging of dust grains in astrophysical environments has been investigated with the assumption these grains are homogeneous spheres. However, there is evidence which suggests many grains in astrophysical environments are irregularly-shaped aggregates. Recent studies have shown that aggregates acquire higher charge-to-mass ratios due to their complex structures, which in turn may alter their subsequent dynamics and evolution. In this paper, the charging of aggregates is examined including secondary electron emission and photoemission in addition to primary plasma currents. The results show that the equilibrium charge on aggregates can differ markedly from spherical grains with the same mass, but that the charge can be estimated for a given environment based on structural characteristics of the grain. The "small particle effect" due to secondary electron emission is also important for determining the charge of micron-sized aggregates consisting of nano-sized particles.