Clusters of tribocharged dust aggregates as pebbles in protoplanetary disks

TL;DR

This study demonstrates that tribocharging of dust aggregates in protoplanetary disks leads to the formation of large, compact clusters, potentially facilitating planetesimal formation by overcoming the bouncing barrier.

Contribution

It is the first to show that not only monolithic particles but also real dust aggregates can become tribocharged and form large clusters in protoplanetary disk conditions.

Findings

Charged dust aggregates form clusters up to 2 cm in size.

Clusters form at collision velocities around 1 cm/s.

Charging can overcome the bouncing barrier, aiding planetesimal formation.

Abstract

In recent years, the tribocharging of colliding and bouncing submillimeter (submm) particles has been studied as a possible mechanism promoting the formation of large pebbles on centimeter (cm) to decimeter (dm) scales in protoplanetary disks. Here, we observe, for the first time, that it is not only monolithic, spherical particles, but also real dust aggregates, that become tribocharged and end up forming large clusters. For aggregates of $\sim 0.4$ mm consisting of $\rm \sim$ 1 $\rm \mu m$ sized dust, we determined net charge densities up to $10^{-7}$ C/$\rm m^2$ during our drop tower experiments. These charged aggregates form compact clusters up to 2 cm in size via collisions with other clusters and aggregates at collision velocities on the order of 1 cm/s. Size and speed are the only lower limits for growth, currently set by the limits of the experiment. However, these clusters already form under conditions that are well beyond the expected transition to bouncing for uncharged aggregates and clusters. Our findings further support the idea that collisional charging can leapfrog the traditional bouncing barrier and form larger clusters that then serve as large pebbles. These cm-sized clusters are more susceptible to further evolutionary steps via particle trapping, concentration, and planetesimal formation.