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

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 of enhancing 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 performed 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.