Charging of aggregate grains in astrophysical environments.

Plasma is a gas in which a portion of particles are ionized. Dust is a ubiquitous component of the universe, and when present in plasma, can form dusty plasma system. Dust in the plasma is generally charged due to the constant collisions with free moving electrons and ions. Cosmic dust can also be charged by other means such as UV and X-ray radiation, and secondary electron emission due to the impact of energetic electrons and ions. The presence of charged dust particles alters the properties of the plasma. The charge on dust grains also affects their dynamics, and influences the coagulation rate. Most previous work assumes that cosmic dust is spherical in shape. However, remote observations and in-situ measurements indicate that cosmic dust is likely to have an aggregate structure. This study examines the charging of aggregate grains in different astrophysical environments. A 3D numerical model employing a self-consistent iterative approach to compute the aggregate charge is introduced. Different size distributions for cosmic dust grains are used in the simulation. The results are compared with previous work on spherical grains, and it is shown that the charging of aggregates differ significantly from that of spheres. Models on predicting charge based on the aggregate structure are proposed, and implications and consequences for future research are discussed.