89 research outputs found
Secular Gravitational Instability of a Dust Layer in Shear Turbulence
We perform a linear stability analysis of a dust layer in a turbulent gas
disk. Youdin (2011) investigated the secular gravitational instability of a
dust layer using hydrodynamic equations with a turbulent diffusion term. We
obtain essentially the same result independently of Youdin (2011). In the
present analysis, we restrict the area of interest to small dust particles,
while investigating the secular gravitational instability in a more rigorous
manner. We discuss the time evolution of the dust surface density distribution
using a stochastic model and derive the advection-diffusion equation. The
validity of the analysis by Youdin (2011) is confirmed in the strong drag
limit. We demonstrate quantitatively that the finite thickness of a dust layer
weakens the secular gravitational instability and that the density-dependent
diffusion coefficient changes the growth rate. We apply the obtained results to
the turbulence driven by the shear instability and find that the secular
gravitational instability is faster than the radial drift when the gas density
is three times as large as that in the minimum-mass disk model. If the dust
particles are larger than chondrules, the secular gravitational instability
grows within the lifetime of a protoplanetary disk.Comment: 32 pages, 6 figures, accepted for publication in Ap
N-Body Simulation of Planetesimal Formation through Gravitational Instability of a Dust Layer in Laminar Gas Disk
We investigate the formation process of planetesimals from the dust layer by
the gravitational instability in the gas disk using local -body simulations.
The gas is modeled as a background laminar flow. We study the formation process
of planetesimals and its dependence on the strength of the gas drag. Our
simulation results show that the formation process is divided into three stages
qualitatively: the formation of wake-like density structures, the creation of
planetesimal seeds, and their collisional growth. The linear analysis of the
dissipative gravitational instability shows that the dust layer is secularly
unstable although Toomre's value is larger than unity. However, in the
initial stage, the growth time of the gravitational instability is longer than
that of the dust sedimentation and the decrease in the velocity dispersion.
Thus, the velocity dispersion decreases and the disk shrinks vertically. As the
velocity dispersion becomes sufficiently small, the gravitational instability
finally becomes dominant. Then wake-like density structures are formed by the
gravitational instability. These structures fragment into planetesimal seeds.
The seeds grow rapidly owing to mutual collisions.Comment: 32 pages, 11 figures, accepted for publication in Ap
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