Gravitational instability of a dust layer composed of porous silicate dust aggregates in a protoplanetary disk

Abstract

Planetesimal formation is one of the most important unsolved problems in planet formation theory. In particular, rocky planetesimal formation is difficult because silicate dust grains are easily broken when they collide. Recently, it has been proposed that they can grow as porous aggregates when their monomer radius is smaller than $\sim$ 10 nm, which can also avoid the radial drift toward the central star. However, the stability of a layer composed of such porous silicate dust aggregates has not been investigated. Therefore, we investigate the gravitational instability of this dust layer. To evaluate the disk stability, we calculate Toomre's stability parameter $Q$, for which we need to evaluate the equilibrium random velocity of dust aggregates. We calculate the equilibrium random velocity considering gravitational scattering and collisions between dust aggregates, drag by mean flow of gas, stirring by gas turbulence, and gravitational scattering by gas density fluctuation due to turbulence. We derive the condition of the gravitational instability using the disk mass, dust-to-gas ratio, turbulent strength, orbital radius, and dust monomer radius. We find that, for the minimum mass solar nebula model at 1 au, the dust layer becomes gravitationally unstable when the turbulent strength $\alpha \lesssim 10^{-5}$. If the dust-to-gas ratio is increased twice, the gravitational instability occurs for $\alpha \lesssim 10^{-4}$. We also find that the dust layer is more unstable in disks with larger mass, higher dust-to-gas ratio, and weaker turbulent strength, at larger orbital radius, and with a larger monomer radius.

arXiv comment17 pages, 11 figures, accepted for publication in ApJ

References in corpus (12)

• Nonlinear Outcome of Gravitational Instability in Cooling, Gaseous Disks
• Particle Stirring in Turbulent Gas Disks: Including Orbital Oscillations
• Rapid Coagulation of Porous Dust Aggregates Outside the Snow Line: A Pathway to Successful Icy Planetesimal Formation
• Protoplanetary Disk Structures in Ophiuchus II: Extension to Fainter Sources
• Fluffy dust forms icy planetesimals by static compression
• On the Formation of Planetesimals via Secular Gravitational Instabilities with Turbulent Stirring
• Static compression of porous dust aggregates
• The Fate of Planetesimals in Turbulent Disks with Dead Zones. I. The Turbulent Stirring Recipe
• $N$-body Simulation of Planetesimal Formation Through Gravitational Instability of a Dust Layer
• Rocky Planetesimal Formation via Fluffy Aggregates of Nanograins
• Planetesimal Formation by Gravitational Instability of a Porous-Dust Disk
• Dynamics of Porous Dust Aggregates and Gravitational Instability of Their Disk

Cited by in corpus (2)

• Geometrical structure and thermal conductivity of dust aggregates formed via ballistic cluster-cluster aggregation
• Nonlinear Outcome of Coagulation Instability in Protoplanetary Disks II: Dust Ring Formation Mediated by Backreaction and Fragmentation