Rapid Dust Growth During Hydrodynamic Clumping Due to Streaming Instability

TL;DR

This paper investigates how dust grains grow rapidly during the early stages of streaming instability-induced clumping, highlighting the significance of local coagulation before strong dust clumping occurs in planetesimal formation.

Contribution

It provides the first estimate of dust growth timescales during the pre-clumping phase of streaming instability, emphasizing the role of coagulation in planetesimal formation.

Findings

Dust growth occurs significantly before strong clumping begins.

Moderate clumping raises local dust-to-gas ratio above 10.

Dust collision velocities can be maintained below 1 m/s, facilitating safe growth.

Abstract

Streaming instability is considered to be one of the dominant processes to promote planetesimal formation by gravitational collapse of dust clumps. The development of streaming instability is expected to form dust clumps in which the local dust density is strongly enhanced and even greater than the Roche density. The resulting clumps can collapse to form planetesimals. Recent simulations conducted long-term simulations and showed that such strong clumping occurs in a wider parameter space than previously expected. However, the indicated timescale for strong clumping can be on the order of tens to hundreds Keplerian periods. In this paper, we estimate the growth time of dust grains during the pre-clumping phase. We find that the dust growth considerably proceeds before the strong clumping because even the moderate clumping due to streaming instability increases the local dust-to-gas ratio $\gtrsim10$. Depending on the gas sound speed, the dust collision velocity can be kept below $\sim 1\;\mathrm{m/s}$ once sufficiently strong dust clumping occurs. Thus, even silicate grains might have the potential to grow safely toward the size whose Stokes number is unity during the clumping. Our results demonstrate the importance of local dust coagulation during the dust clumping due to streaming instability.