Protostellar collapse simulations in spherical geometry with dust coagulation and fragmentation

TL;DR

This study models dust coagulation and fragmentation during protostellar collapse, revealing significant dust size evolution, the influence of turbulence and magnetic fields, and highlighting the importance of including dust processes in collapse simulations.

Contribution

It introduces a new simulation code that couples gas-dust hydrodynamics with dust coagulation and fragmentation, providing insights into dust evolution and magnetic resistivities during collapse.

Findings

Dust size distribution evolves significantly during collapse.

Magnetic fields enhance small grain depletion and ambipolar diffusion.

Fragmentation effects depend on dust composition and are still uncertain.

Abstract

We model the coagulation and fragmentation of dust grains during the protostellar collapse with our newly developed shark code. It solves the gas-dust hydrodynamics in a spherical geometry and the coagulation/fragmentation equation. It also computes the ionization state of the cloud and the Ohmic, ambipolar and Hall resistivities. We find that the dust size distribution evolves significantly during the collapse, large grain formation being controlled by the turbulent differential velocity. When turbulence is included, only ambipolar diffusion remains efficient at removing the small grains from the distribution, brownian motion is only efficient as a standalone process. The macroscopic gas-dust drift is negligible for grain growth and only dynamically significant near the first Larson core. At high density, we find that the coagulated distribution is unaffected by the initial choice of dust distribution. Strong magnetic fields are found to enhance the small grains depletion, causing an important increase of the ambipolar diffusion. This hints that the magnetic field strength could be regulated by the small grain population during the protostellar collapse. Fragmentation could be effective for bare silicates, but its modeling relies on the choice of ill-constrained parameters. It is also found to be negligible for icy grains. When fragmentation occurs, it strongly affects the magnetic resistivities profiles. Dust coagulation is a critical process that needs to be fully taken into account during the protostellar collapse. The onset and feedback of fragmentation remains uncertain and its modeling should be further investigated.