Can planetesimals form by collisional fusion?

TL;DR

This study uses detailed simulations to analyze dust-boulder collisions in protoplanetary disks, testing the collisional fusion hypothesis as a mechanism for planetesimal formation.

Contribution

It provides a detailed numerical analysis of collision velocities and evaluates the viability of collisional fusion in planetesimal growth.

Findings

Collision velocity PDFs support collisional fusion at certain velocities.

Collisional fusion can enable rapid growth of boulders into planetesimals.

Boulder growth timescales are compatible with disk evolution periods.

Abstract

As a test bed for the growth of protoplanetary bodies in a turbulent circumstellar disk we examine the fate of a boulder using direct numerical simulations of particle seeded gas flowing around it. We provide an accurate description of the flow by imposing no-slip and non-penetrating boundary conditions on the boulder surface using the immersed boundary method pioneered by Peskin (2002). Advected by the turbulent disk flow, the dust grains collide with the boulder and we compute the probability density function (PDF) of the normal component of the collisional velocity. Through this examination of the statistics of collisional velocities we test the recently developed concept of collisional fusion which provides a physical basis for a range of collisional velocities exhibiting perfect sticking. A boulder can then grow sufficiently rapidly to settle into a Keplerian orbit on disk evolution time scales.