The effect of dust composition and shape on radiation-pressure forces and blowout sizes of particles in debris disks

TL;DR

This study investigates how realistic irregular dust grain shapes and compositions affect radiation-pressure blowout sizes in debris disks, revealing significant differences from traditional spherical models and emphasizing the importance of particle morphology.

Contribution

It introduces the use of the discrete dipole approximation to model irregular dust grains, providing more accurate blowout size estimates that depend on shape and composition.

Findings

Irregular grain shapes lead to larger blowout sizes compared to spherical models.

Dust composition affects blowout sizes, with absorptive grains being more easily removed.

Differences in blowout sizes can be as large as an order of magnitude depending on particle morphology.

Abstract

The light scattered from dust grains in debris disks is typically modeled as compact spheres using Lorenz-Mie theory or as porous spheres by incorporating an effective medium theory. In this work we examine the effect of incorporating a more realistic particle morphology on estimated radiation-pressure blowout sizes. To calculate the scattering and absorption cross sections of irregularly shaped dust grains, we use the discrete dipole approximation. These cross sections are necessary to calculate the $\beta$-ratio, which determines whether dust grains can remain gravitationally bound to their star. We calculate blowout sizes for a range of stellar spectral types corresponding with stars known to host debris disks. As with compact spheres, more luminous stars blow out larger irregularly shaped dust grains. We also find that dust grain composition influences blowout size such that absorptive grains are more readily removed from the disk. Moreover, the difference between blowout sizes calculated assuming spherical particles versus particle morphologies more representative of real dust particles is compositionally dependent as well, with blowout size estimates diverging further for transparent grains. We find that the blowout sizes calculated have a strong dependence on the particle model used, with differences in the blowout size calculated being as large as an order of magnitude for particles of similar porosities.