Rotational Disruption of Porous Dust Aggregates due to Gas Flow in Protoplanetary Disks

Abstract

We introduce a possible disruption mechanism of dust grains in planet formation by their spinning motion. 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 whether 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. We model the irregularly shaped dust aggregates by introducing a parameter, γ ft, that mimics the conversion efficiency from force to torque. 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. 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. We also note that dust aggregates are not rotationally disrupted when γ ft ≤ 0.02 in our fiducial model and the modeling of irregularly shaped dust aggregates is essential in future work.

Dust grain shattering in protoplanetary discs: collisional fragmentation or rotational disruption?

“…Recently, Tatsuuma & Kataoka (2021) presented a new barrier to dust growth: the rotational disruption barrier. Rotational disruption has already been investigated for interstellar medium dust (Hoang et al 2019) or cometary dust (Tung & Hoang 2020), but not in the case of protoplanetary discs.…”

“…We decide to investigate whether disruption occurs before or after the onset of fragmentation, under which circumstances it happens, and whether disruption plays a role in dust growth. Following Tatsuuma & Kataoka (2021), we suppose that our grains are always in a steady-state angular velocity regime to be able to compute the angular velocity 𝜔 c . We assume that 𝜔 c is driven only by the gas-flow torque.…”

“…The intrinsic density of water ice monomers is 𝜌 s = 1000 kg m −3 with a surface energy of 𝛾 s = 0.1 J m −2 . As the critical rolling displacement is uncertain and still under debate, we choose 𝜉 crit = 8 Å (Wada et al 2011;Tatsuuma & Kataoka 2021), and the fragmentation threshold for water ice is set to 𝑣 frag,H2O = 15 m s −1 (e.g. Gonzalez et al 2015, see also Sect.…”

“…Recently, rotational disruption of porous dust grains was proposed as another possible barrier and has been investigated by Tatsuuma & Kataoka (2021) in the framework of protoplanetary discs. They found that grains can be disrupted by the gas-flow torque when aggregates tend to be highly porous, before they can decouple from the gas, when very compact grains are not.…”

On Internal and External Alignment of Dust Grains in Protostellar Environments

“…For example, grains are usually assumed to be aligned with the shortest axis (â 1 ) perfectly aligned with the magnetic field or radiation direction (Ohashi et al 2018(Ohashi et al , 2020Kataoka et al 2019;Yang et al 2018;Harrison et al 2019). That assumption disregarded the important effect of internal alignment (e.g., Mori & Kataoka 2021;Lin et al 2021;Tatsuuma & Kataoka 2021), which does not ensure that the inferred magnetic fields are accurate.…”