Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the gravitational stability of gravito-turbulent accretion disks   Low mass, self-gravitating accretion disks admit
quasi-steady,`gravito-turbulent' states in which cooling balances turbulent
viscous heating. However, numerical simulations show that gravito-turbulence
cannot be sustained beyond dynamical timescales when the cooling rate or
corresponding turbulent viscosity is too large. The result is disk
fragmentation. We motivate and quantify an interpretation of disk fragmentation
as the inability to maintain gravito-turbulence due to formal secondary
instabilities driven by: 1) cooling, which reduces pressure support; and/or 2)
viscosity, which reduces rotational support. We analyze the axisymmetric
gravitational stability of viscous, non-adiabatic accretion disks with internal
heating, external irradiation, and cooling in the shearing box approximation.
We consider parameterized cooling functions in 2D and 3D disks, as well as
radiative diffusion in 3D. We show that generally there is no critical cooling
rate/viscosity below which the disk is formally stable, although interesting
limits appear for unstable modes with lengthscales on the order of the disk
thickness. We apply this new linear theory to protoplanetary disks subject to
gravito-turbulence modeled as an effective viscosity, and cooling regulated by
dust opacity. We find that viscosity renders the disk beyond $\sim 60$AU
dynamically unstable on radial lengthscales a few times the local disk
thickness. This is coincident with the empirical condition for disk
fragmentation based on a maximum sustainable stress. We suggest turbulent
stresses can play an active role in realistic disk fragmentation by removing
rotational stabilization against self-gravity, and that the observed transition
in behavior from gravito-turbulent to fragmenting may reflect instability of
the gravito-turbulent state itself.

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The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
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The categories of this paper are: eess
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
24
The categories of this paper are: dg-ga
3
The categories of this paper are: physics
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg
21
The categories of this paper are: adap-org
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph