Evading the dust fragmentation barrier with the streaming instability in protoplanetary disks

TL;DR

This paper demonstrates that the streaming instability can promote dust growth and clumping in protoplanetary disks, overcoming growth barriers and aiding planetesimal formation through a feedback loop between dust size and density.

Contribution

It introduces a two-dimensional simulation showing how dust mass loading enhances dust growth and clumping via the streaming instability, addressing dust fragmentation barriers.

Findings

Dust mass loading reduces collision velocities, enabling larger dust particles.

Dust growth and clumping mutually reinforce each other, promoting planetesimal formation.

Denser dust clumps form when initial dust-to-gas ratio and dust properties are favorable.

Abstract

Context: The streaming instability (SI) is a leading candidate for reaching solid densities sufficient to trigger the gravitational collapse needed for the formation of planetesimals. However, dust growth barriers appear to impede the ability to assemble sufficiently large dust particles to trigger strong clumping, providing a serious impediment to planetesimal formation. Aims: We aim to address the possibility to enhance dust clumping with dust growth in SI-produced structures, and to estimate the impact of the shift of the dust fragmentation threshold in regions where the SI has enhanced the dust density. Methods: We perform two-dimensional numerical simulations of the SI with a monodisperse description of dust growth, accounting for the impact of mass loading of the dust on the sound speed of the gas and dust mixture when computing dust collisional velocities. Results: Dust mass loading reduces collision velocities in high density regions, allowing dust particles to survive to larger sizes before shattering. In turn, dust clumping is boosted as particles grow in size, as long as they remain sufficiently coupled to the gas. Conclusions: This two-way synergy between dust growth and clumping, which depends on the initial dust-to-gas ratio and dust elastic properties, allows denser dust clumps to form and thus facilitates the onset of planetesimal formation.