2:30 PM - 2:45 PM
[PPS06-19] Physics of dust collision in streaming instability : effect of dust size distribution
Keywords:Protoplanetary disks, Planetesimals
The formation process of kilometer-sized planetesimals remains an unresolved issue with many uncertainties. The most widely accepted theory for the formation of planetesimals at present is the formation of high-density dust clumps due to streaming instability (e.g., Johansen & Youdin 2007, Yang & Zhu 2021). Dust clumps are expected to induce gravitational instability, leading to the formation of planetesimals. However, there are still unresolved problems related to streaming instability. For high-density dust clumps to induce gravitational instability at the dust-gas ratio of 0.01, the size of the dust grains must be several centimeters or larger. This raises the question of whether such growth to these sizes is possible. Moreover, the formation of high-density dust clumps takes longer for smaller dust grains (e.g.,Li & Youdin 2021), suggesting that relatively larger dust sizes are required to form high-density clumps before dust falls (Carrera & Simon 2022).
We examine the dust collision process and the growth process during the development of the streaming instability to clarify the evolution of dust size, which plays a crucial role in the instability. In our previous study, we conducted axisymmetric 2D hydrodynamical simulations of the streaming instability to investigate the dust collision velocities and growth rates. The results showed that dust with low-velocity collisions grows rapidly into high-density clumps. In this study, in order to derive empirical formulas for collision velocities and growth rates, we have conducted many hydrodynamical simulations of the streaming instability with varying parameters such as dust size, dust-to-gas density ratio, and the presence of a dust size distribution, and we have examined the dependencies on them.
In hydrodynamical simulations with a single dust size, we have found that increasing the dust-to-gas density ratio further develops the streaming instability, leading to increased dust densities in clumps and collision velocities due to this instability. On the other hand, in simulations with dust size distributions, the instability develops primarily with the larger dust components. We also found that the presence of smaller dust particles suppresses the development of the instability, significantly reducing the increase in dust densities in clumps and collision velocities. Furthermore, for both calculations with and without a dust size distribution, we have successfully derived empirical formulas for the average values of dust collision velocity, dust clump density, and dust growth rate for both monodiverse and polydiverse dust size simulations. By using these empirical formulas for collision velocities and growth rates, it will be possible to accurately discuss the dust growth process during the development of the streaming instability.
We examine the dust collision process and the growth process during the development of the streaming instability to clarify the evolution of dust size, which plays a crucial role in the instability. In our previous study, we conducted axisymmetric 2D hydrodynamical simulations of the streaming instability to investigate the dust collision velocities and growth rates. The results showed that dust with low-velocity collisions grows rapidly into high-density clumps. In this study, in order to derive empirical formulas for collision velocities and growth rates, we have conducted many hydrodynamical simulations of the streaming instability with varying parameters such as dust size, dust-to-gas density ratio, and the presence of a dust size distribution, and we have examined the dependencies on them.
In hydrodynamical simulations with a single dust size, we have found that increasing the dust-to-gas density ratio further develops the streaming instability, leading to increased dust densities in clumps and collision velocities due to this instability. On the other hand, in simulations with dust size distributions, the instability develops primarily with the larger dust components. We also found that the presence of smaller dust particles suppresses the development of the instability, significantly reducing the increase in dust densities in clumps and collision velocities. Furthermore, for both calculations with and without a dust size distribution, we have successfully derived empirical formulas for the average values of dust collision velocity, dust clump density, and dust growth rate for both monodiverse and polydiverse dust size simulations. By using these empirical formulas for collision velocities and growth rates, it will be possible to accurately discuss the dust growth process during the development of the streaming instability.