Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Forming Planetesimals by Gravitational Instability: I. The Role of the
  Richardson Number in Triggering the Kelvin-Helmholtz Instability   Gravitational instability (GI) of a dust-rich layer at the midplane of a
gaseous circumstellar disk is one proposed mechanism to form planetesimals, the
building blocks of rocky planets and gas giant cores. Self-gravity competes
against the Kelvin-Helmholtz instability (KHI): gradients in dust content drive
a vertical shear which risks overturning the dusty subdisk and forestalling GI.
To understand the conditions under which the disk can resist the KHI, we
perform 3D simulations of stratified subdisks in the limit that dust particles
are small and aerodynamically well coupled to gas. This limit screens out the
streaming instability and isolates the KHI. Each subdisk is assumed to have a
vertical density profile given by a spatially constant Richardson number Ri. We
vary Ri and the midplane dust-to-gas ratio mu and find that the critical
Richardson number dividing KH-unstable from KH-stable flows is not unique;
rather Ri_crit grows nearly linearly with mu for mu=0.3-10. Only for disks of
bulk solar metallicity is Ri_crit ~ 0.2, close to the classical value. Our
results suggest that a dusty sublayer can gravitationally fragment and
presumably spawn planetesimals if embedded within a solar metallicity gas disk
~4x more massive than the minimum-mass solar nebula; or a minimum-mass disk
having ~3x solar metallicity; or some intermediate combination of these two
possibilities. Gravitational instability seems possible without resorting to
the streaming instability or to turbulent concentration of particles.

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The categories of this paper are: mtrl-th
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The categories of this paper are: funct-an
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The categories of this paper are: q-bio
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The categories of this paper are: chem-ph
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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
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The categories of this paper are: solv-int
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The categories of this paper are: q-fin
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The categories of this paper are: econ
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The categories of this paper are: plasm-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: gr-qc
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The categories of this paper are: math
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The categories of this paper are: quant-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: chao-dyn