2019-07-03

Title: Rotational Disruption of Irregularly-shaped Dust Aggregates in Planetesimal Formation

Misako Tatsuuma (Univ. of Tokyo)

Abstract:

In recent years, polarized emission at millimeter wavelength in protoplanetary disks has been observed, some of which are interpreted as the emission of aligned elongated dust grains. For such dust alignment to occur, it is believed that irregularly-shaped dust grains rotate. In the interstellar space, it has been pointed out that dust grains rotate due to torque by the interstellar radiation and are disrupted by centrifugal force (Hoang 2019, ApJ, 876, 13). In this process, the centrifugal force due to the rotational motion, that is tensile stress, is applied to the dust grains and they are disrupted if the tensile stress is larger than their tensile strength.
     In this work, we theoretically calculate whether or not dust grains are rotationally disrupted during their coagulation in a protoplanetary disk. We use the tensile strength of porous dust aggregates (Tatsuuma et al. 2019, ApJ, 874, 159). We assume two driving sources of the rotational motion of the dust aggregates: the torques from the radiation field and the gas flow in the disk. We calculate the constant rotational velocity of the dust aggregates by assuming that their rotational motion is damped by the surrounding gas and we obtain the tensile stress due to the centrifugal force. As a result, we find that highly porous dust aggregates are disrupted if their mass is larger than ~ 10^{10} g. We also find that the dominant driving source of the torque is not the radiation field but the gas flow, unlike in the interstellar space. This is due to the weak energy density of the radiation field at the disk midplane compared to that in the interstellar space. The results suggest that the growth of irregularly-shaped dust aggregates can be halted due to rotational disruption if they are highly porous. 

Host contact: Akimasa Kataoka