Investigating the Bouncing Barrier with Collision Simulations of Compressed Dust Aggregates

TL;DR

This study uses collision simulations of compressed dust aggregates to understand the bouncing barrier in planetesimal formation, revealing how impact velocity and filling factor influence bouncing thresholds and aggregate growth limits.

Contribution

It introduces a novel simulation approach generating compact aggregates via compression, and quantifies how impact velocity and filling factor affect bouncing thresholds and energy dissipation.

Findings

Bouncing occurs above a threshold mass decreasing with impact velocity.

Threshold mass scales with impact velocity as v^(-4/3).

Aggregates with filling factor 0.4 stop growing beyond 100 μm due to bouncing.

Abstract

The collision outcomes of dust aggregates in protoplanetary disks dictate how planetesimals form. Experimental and numerical studies have suggested that bouncing collisions occurring at low impact velocities may limit aggregate growth in the disks, but the conditions under which bouncing occurs have yet to be fully understood. In this study, we perform a suite of collision simulations of moderately compact dust aggregates with various impact velocities, aggregate radii, and filling factors ranging between 0.4 and 0.5. Unlike previous simulations, we generate compact aggregates by compressing more porous ones, mimicking the natural processes through which compact aggregates form. We find that the compressed aggregates bounce above a threshold mass, which decreases with impact velocity. The threshold mass scales with impact velocity as the $-4/3$ power, consistent with the findings of previous experiments. We also find that the threshold aggregate mass for bouncing depends strongly on filling factor, likely reflecting the strong filling-factor dependence of the compressive strength of compressed aggregates. Our energy analysis reveals that nearly 90\% of the initial impact energy is dissipated during the initial compression phase, and over 70\% of the remaining energy is dissipated during the subsequent stretching phase, regardless of whether the collision results in sticking or bouncing. Our results indicate that dust aggregates with a filling factor of 0.4 cease to grow beyond 100 $\mathrm{\mu m}$ as a result of the bouncing barrier.