2:30 PM - 2:45 PM
[PPS07-14] On collisional growth of dust grains promoted by streaming instability in protoplanetary disks
Keywords:protoplanetary disk, dust, planetesimal formation
Planetesimals are the building blocks of planets. Understanding how planetesimals form in protoplanetary disks is important to reveal planet formation. Previous studies showed that some processes can prevent planetesimal formation via dust coagulation. One of the obstacles is collisional fragmentation (e.g., Blum & Wurm 2008). Streaming instability was proposed as a possible solution (e.g., Youdin & Goodman 2005). The instability leads to aerodynamic clumping of dust grains. The resulting clumps can be massive enough and collapse self-gravitationally (e.g., Johansen et al. 2009; Simon et al. 2017). Such strong clumping and the subsequent self-gravitational collapse are expected to explain planetesimal formation. However, the clumping efficiency depends on the Stokes number (i.e., dust sizes) and is high for the Stokes number of ~0.1-1 (e.g., Bai & Stone 2010). Depending on turbulence strength and disk temperature, this required dust size can be larger than the fragmentation-limited dust sizes. Therefore, some processes to mitigate collisional fragmentation are still necessary. In this work, we investigate dust growth in moderately clumped regions where collision velocities are expected to be low (e.g., Johansen et al. 2009). First, we estimate coagulation timescale based on collision velocities measured in the previous studies (Bai & Stone 2010; Schreiber & Klahr 2018). We find that coagulation timescale can be comparable to or shorter than a timescale on which massive clumps form (Li & Youdin 2021). This indicates that dust growth and clumping proceed simultaneously. We then perform two-dimensional numerical simulations of streaming instability and measure collision rates. The results show that dust collisions are frequent in moderately clumped regions, and the collision velocity can be on the order of 0.1 percent of sound speed. This may help dust to avoid significant fragmentation and accelerate the clumping due to streaming instability on the coagulation timescale.