[PPS09-02] Tensile Strength and Rotational Disruption of Porous Dust Aggregates in Protoplanetary Disks
Keywords:Planetesimal Formation, Protoplanetary Disks, Tensile Strength, Dust Aggregates, Planetesimals
The first step toward planet formation is coagulation of dust grains in protoplanetary disks. Their growth may be halted, for example, by their collisional disruption, which is thought to explain the observed submillimeter–centimeter size of dust grains in protoplanetary disks. Here, we introduce another disruption mechanism by spinning motion of dust grains in planet formation. This mechanism has been discussed as rotational disruption for the interstellar dust grains. We theoretically calculate whether porous dust aggregates can be disrupted by their spinning motion and if it prohibits dust growth in protoplanetary disks. We assume radiative torque and gas-flow torque as driving sources of the spinning motion, assume that dust aggregates reach a steady-state rigid rotation, and compare the obtained tensile stress due to the centrifugal force with their tensile strength calculated by using dust N-body simulations. As a result, we find that porous dust aggregates are rotationally disrupted by their spinning motion induced by gas flow when their mass is larger than 108 g and their volume filling factor is smaller than 0.01 in our fiducial model, while relatively compact dust aggregates with volume filling factor more than 0.01 do not face this problem. Also, we find that the radiative torque on dust aggregates is much weaker than gas-flow torque in protoplanetary disks. If we assume the dust porosity evolution, we find that dust aggregates whose Stokes number is 0.1 can be rotationally disrupted in their growth and compression process. Our results suggest that the growth of dust aggregates may be halted due to rotational disruption or that other compression mechanisms are needed to avoid it.