11:45 AM - 12:00 PM
[PPS06-15] Growth Limits of Icy Dust Aggregates Due to the Bouncing Barrier: Consistency with Millimeter-Wave Polarimetric Observations
Keywords:Protoplanetary disk, Dust aggregate, Planetesimal formation, Pebbles, Polarization observation
Planet formation begins with the formation of dust aggregates through the coagulation of micron-sized dust grains in protoplanetary disks. According to previous theories of dust growth, the icy dust aggregates that are ingredients of icy planetesimals have high porosity and can grow to over the centimeter sizes (e.g., Suyama et al. 2008). However, recent millimeter-wave polarization observations of disks have revealed that the maximum aggregate sizes are limited to 0.1-1 mm, with high internal densities (filling factor >0.1) (e.g., Zhang et al. 2023; Ueda et al. 2024). These observations imply the existence of processes within the disk that compress icy dust aggregates and inhibit their growth.
In this study, we focus on bouncing, which can occur even at relatively low collision velocities, as a potential factor inhibiting the growth of icy aggregates. It is known that when compact dust aggregates collide at certain velocities, they bounce without sticking or undergoing significant fragmentation (Güttler et al. 2010). We have previously performed systematic numerical collision simulations of compressed aggregates to determine the collision velocities, aggregate masses, and filling factors under which bouncing occurs (Oshiro et al., submitted). Our calculations show that the maximum velocity at which aggregates can stick without bouncing (the critical bouncing velocity) scales with the aggregate mass to the power of -3/4. This scaling is consistent with previous laboratory experiments (Kothe et al. 2013).
In this study, we use the critical bouncing scaling formula velocity obtained in our previous work to investigate the extent to which bouncing inhibits dust growth in protoplanetary disks. Specifically, we calculate the relative velocities (collision velocities) of icy dust particles, arising from turbulence and other effects in the disk, as a function of dust size. By comparing these velocities with the critical bouncing velocity, we estimated the maximum size of icy dust aggregates that can grow via accretion without bouncing. Since bouncing tends to lead to a uniform dust size distribution (Dominik & Dullemond 2024), we assumed equal sizes for colliding aggregates to determine their collision velocities.
Our results show that when the filling factor exceeds 0.4, the maximum size of icy dust aggregates that can grow without bouncing is approximately 0.1 mm, independent of the filling factor in this range. On the other hand, for lower filling factors, the maximum size increases, but the increase is limited to a factor of ten. These findings suggest that the observed maximum dust size of 0.1–1 mm in millimeter-wave polarization observations of disks may be due to the bouncing barrier. Furthermore, the limited aggregate sizes suggested in this study can be widely applied in planetary science, including planetesimal formation due to dust concentration in the smallest turbulent eddies (Cuzzi et al. 2001) or tribocharged aggregate clusters (e.g., Teiser et al. 2025), and the formation of chondrules in meteorites (Ebel et al. 2016).
In this study, we focus on bouncing, which can occur even at relatively low collision velocities, as a potential factor inhibiting the growth of icy aggregates. It is known that when compact dust aggregates collide at certain velocities, they bounce without sticking or undergoing significant fragmentation (Güttler et al. 2010). We have previously performed systematic numerical collision simulations of compressed aggregates to determine the collision velocities, aggregate masses, and filling factors under which bouncing occurs (Oshiro et al., submitted). Our calculations show that the maximum velocity at which aggregates can stick without bouncing (the critical bouncing velocity) scales with the aggregate mass to the power of -3/4. This scaling is consistent with previous laboratory experiments (Kothe et al. 2013).
In this study, we use the critical bouncing scaling formula velocity obtained in our previous work to investigate the extent to which bouncing inhibits dust growth in protoplanetary disks. Specifically, we calculate the relative velocities (collision velocities) of icy dust particles, arising from turbulence and other effects in the disk, as a function of dust size. By comparing these velocities with the critical bouncing velocity, we estimated the maximum size of icy dust aggregates that can grow via accretion without bouncing. Since bouncing tends to lead to a uniform dust size distribution (Dominik & Dullemond 2024), we assumed equal sizes for colliding aggregates to determine their collision velocities.
Our results show that when the filling factor exceeds 0.4, the maximum size of icy dust aggregates that can grow without bouncing is approximately 0.1 mm, independent of the filling factor in this range. On the other hand, for lower filling factors, the maximum size increases, but the increase is limited to a factor of ten. These findings suggest that the observed maximum dust size of 0.1–1 mm in millimeter-wave polarization observations of disks may be due to the bouncing barrier. Furthermore, the limited aggregate sizes suggested in this study can be widely applied in planetary science, including planetesimal formation due to dust concentration in the smallest turbulent eddies (Cuzzi et al. 2001) or tribocharged aggregate clusters (e.g., Teiser et al. 2025), and the formation of chondrules in meteorites (Ebel et al. 2016).