Revised Description of Dust Diffusion and a New Instability Creating Multiple Rings in Protoplanetary Disks

Abstract

Various instabilities have been proposed as a promising mechanism to accumulate dust. Moreover, some of them are expected to lead to the multiple-ring structure formation and the planetesimal formation in protoplanetary disks. In a turbulent gaseous disk, the growth of the instabilities and the dust accumulation are quenched by turbulent diffusion of dust grains. The diffusion process has been often modeled by a diffusion term in the continuity equation for the dust density. The dust diffusion model, however, does not guarantee the angular momentum conservation in a disk. In this study, we first formulate equations that describe the dust diffusion and also conserve the total angular momentum of a disk. Second, we perform the linear perturbation analysis on the secular gravitational instability (GI) using the equations. The results show that the secular GI is a monotonically growing mode, contrary to the result of previous analyses that found it overstable. We find that the overstability is caused by the non-conservation of the angular momentum. Third, we find a new axisymmetric instability due to the combination of the dust-gas friction and the turbulent gas viscosity, which we refer to as two-component viscous gravitational instability (TVGI). The most unstable wavelength of TVGI is comparable to or smaller than the gas scale height. TVGI accumulates dust grains efficiently, which indicates that TVGI is a promising mechanism for the formation of multiple-ring-like structures and planetesimals. Finally, we examine the validity of the ring formation via the secular GI and TVGI in the HL Tau disk and find both instabilities can create multiple rings whose width is about 10 au at orbital radii larger than 50 au.

Global three-dimensional simulations of outer protoplanetary discs with ambipolar diffusion

“…To name but a few, one set of proposed mechanisms is related to the condensation fronts of various volatile species, which mark a transition in dust properties (e.g., Zhang et al 2015;Okuzumi et al 2016;Hu et al 2019;Owen 2020). Another set of scenarios is associated with gas-dust coupling, including secular gravitational instability (Shariff & Cuzzi 2011;Youdin 2011;Takahashi & Inutsuka 2014;Tominaga et al 2018Tominaga et al , 2019, dust-driven viscous ring-instability (Wünsch et al 2005;Dullemond & Penzlin 2018), and self-induced dust traps (Drazkowska et al 2016;Gonzalez et al 2017).…”

Planet formation by pebble accretion in ringed disks

“…Magnetohydrodynamical (MHD) simulations show that the surface density distribution of disks can become a radial wavy function (Bethune et al 2017), leading to the formation of multiple pressure bumps and hence of dust rings (Riols et al 2019). More subtle dust-gas instabilities can also generate dust rings (Tominaga et al 2019). On the other hand, massive planets can open gaps in the gas distribution and generate pressure bumps (e.g., Zhang et al 2018;Weber et al 2017;Yang & Zhu 2020;Wafflard-Fernandez & Baruteau 2020).…”

Distant Formation and Differentiation of Outer Main Belt Asteroids and Carbonaceous Chondrite Parent Bodies

“…We suggest that there might be multiple pressure traps to separate reservoirs. Possible origins of pressure traps include gas‐dust viscous gravitational instability (Tominaga et al., 2019), magneto‐hydrodynamical wind (Taki et al., 2021), sublimation near the snow line(s) (Charnoz et al., 2021), and disk–planet interaction (Kanagawa et al., 2015). Such multiple pressure traps in a single protoplanetary disk are thought to create ringed structures which were found to be common in protoplanetary disks observed recently by the Atacama Large Millimeter/submillimeter Array (the spacial scales of rings are several tens of au, Andrews et al., 2018; Dullemond et al., 2018).…”