Gravito-Turbulent Disks in Three Dimensions: Turbulent Velocities Versus Depth

Shi, Ji-Ming; Chiang, Eugene

doi:10.1088/0004-637x/789/1/34

Cited by 49 publications

(69 citation statements)

References 55 publications

(98 reference statements)

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“…used a Fourier analysis of GI in the shearing sheet approximation to show that the power spectrum of perturbations generated by the instability is contained in modes with wavelengths of a few H. Gammie (2001) finds essentially no power at scales much smaller than H, which are resolved in the calculations. A similar result has recently been obtained by Shi & Chiang (2014) using three dimensional shearing box simulations. Young & Clarke (2015) also show -in the context of fragmentation (see below) -that collapse of unstable modes is never initiated on scales H. These results imply that 'gravito-turbulence' extends over a very small range of lengthscales.…”

Section: The Onset Of Linear Instabilitysupporting

confidence: 89%

“…As a result, measurement of the fragmentation boundary (or stochastic fragmentation) in a 2D simulation is questionable, and better left to 3D simulations. They further argue that because of the quasi-regular nature of selfgravitating structures, stochastic fragmentation should be inhibited at very large β, because the growth and development of spiral structure occurs over a modest number of orbital periods, and thus may not be akin to a true turbulent cascade (see also Shi & Chiang (2014)). …”

Section: Convergence Of Numerical Resultsmentioning

confidence: 99%

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Gravitational Instabilities in Circumstellar Disks

Kratter

Lodato

2016

Annu. Rev. Astron. Astrophys.

454

380

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Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability, and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability, supplemented with a survey of numerical simulations that aim to capture the non-linear evolution. We emphasize the role of thermodynamics and large scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analytic predictions and numerical results. In the next part of our review, we focus on the astrophysical consequences of the instability. We show that the disks most likely to be gravitationally unstable are young and relatively massive compared to their host star, M d /M * ≥ 0.1. They will develop quasi-stable spiral arms that process infall from the background cloud. While instability is less likely at later times, once infall becomes less important, the manifestations of the instability are more varied. In this regime, the disk thermodynamics, often regulated by stellar irradiation, dictates the development and evolution of the instability. In some cases the instability may lead to fragmentation into bound companions. These companions are more likely to be brown dwarfs or stars than planetary mass objects. Finally, we highlight open questions related to (1) the development of a turbulent cascade in thin disks, and (2) the role of mode-mode coupling in setting the maximum angular momentum transport rate in thick disks. We dedicate this article to the memory of Francesco Palla, who has been a source of inspiration for star formation and disk studies throughout the years. Through his support and encouragement of young scientists, his contributions live on.

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Section: The Onset Of Linear Instabilitysupporting

confidence: 89%

Section: Convergence Of Numerical Resultsmentioning

confidence: 99%

Gravitational Instabilities in Circumstellar Disks

Kratter

Lodato

2016

Annu. Rev. Astron. Astrophys.

454

380

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“…Their figure 7 shows an increase in the velocity dispersion with vertical position in the disk. Shi & Chiang (2014) note that these high latitudes are not unstable by themselves but are forced to be turbulent by long-range gravitational forces from mass perturbations centered on the midplane. Observations of the variation of gas velocity dispersion with height in a galaxy might distinguish between gravity-driven turbulence and stellar-feedback driven turbulence on the scale of the disk thickness.…”

Section: Discussionmentioning

confidence: 97%

The Kennicutt–Schmidt Law and Gas Scale Height in Luminous and Ultraluminous Infrared Galaxies

Wilson

Elmegreen

Bemis

et al. 2019

ApJ

118

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A new analysis of high-resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA) for 5 luminous or ultra-luminous infrared galaxies gives a slope for the Kennicutt-Schmidt (KS) relation equal to 1.74 +0.09 −0.07 for gas surface densities Σ mol > 10 3 M pc −2 and an assumed constant CO-to-H 2 conversion factor. The velocity dispersion of the CO line, σ v , scales approximately as the inverse square root of Σ mol , making the empirical gas scale height determined from H ∼ 0.5σ 2 /(πGΣ mol ) nearly constant, 150-190 pc, over 1.5 orders of magnitude in Σ mol . This constancy of H implies that the average midplane density, which is presumably dominated by CO-emitting gas for these extreme star-forming galaxies, scales linearly with the gas surface density, which, in turn, implies that the gas dynamical rate (the inverse of the free-fall time) varies with Σ 1/2 mol , thereby explaining most of the super-linear slope in the KS relation. Consistent with these relations, we also find that the mean efficiency of star formation per free-fall time is roughly constant, 5%-7%, and the gas depletion time decreases at high Σ mol , reaching only ∼ 16 Myr at Σ mol ∼ 10 4 M pc −2 . The variation of σ v with Σ mol and the constancy of H are in tension with some feedback-driven models, which predict σ v to be more constant and H to be more variable. However, these results are consistent with simulations in which large-scale gravity drives turbulence through a feedback process that maintains an approximately constant Toomre Q instability parameter.

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“…The Reynolds stress in GI fluctuates with radius and possesses negative values at some radii, and tracks the quasi-steady spiral structure. However, its contribution to the total stress is negligible in the simulations without magnetic field (see also Shi & Chiang 2014;Booth & Clarke 2018). Interestingly, the Reynolds stress increases in the GI-MHD simulations, with an averaged value 0.034 for grvmhd1 and 0.035 for grvmhd2.…”

Section: Turbulent Transportmentioning

confidence: 91%

Global Simulations of Self-gravitating Magnetized Protoplanetary Disks

Deng

Mayer²,

Latter

2020

ApJ

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In the early stages of a protoplanetary disk, when its mass is a significant fraction of its star's, turbulence generated by gravitational instability (GI) should feature significantly in the disk's evolution. At the same time, the disk may be sufficiently ionised for magnetic fields to play some role in the dynamics. Though usually neglected, the impact of magnetism on the GI may be critical, with consequences for several processes: the efficiency of accretion, spiral structure formation, fragmentation, and the dynamics of solids. In this paper, we report on global three-dimensional magnetohydrodynamical simulations of a self-gravitating protoplanetary disk using the meshless finite mass (MFM) Lagrangian technique. We confirm that GI spiral waves trigger a dynamo that amplifies an initial magnetic field to nearly thermal amplitudes (plasma β < 10), an order of magnitude greater than that generated by the magnetorotational instability alone. We also determine the dynamo's nonlinear back reaction on the gravitoturbulent flow: the saturated state is substantially hotter, with an associated larger Toomre parameter and weaker, more 'flocculent' spirals. But perhaps of greater import is the dynamo's boosting of accretion via a significant Maxwell stress; mass accretion is enhanced by factors of several relative to either pure GI or pure MRI. Our simulations use ideal MHD, an admittedly poor approximation in protoplanetary disks, and thus future studies should explore the full gamut of non-ideal MHD. In preparation for that, we exhibit a small number of Ohmic runs that reveal that the dynamo, if anything, is stronger in a non-ideal environment. This work confirms that magnetic fields are a potentially critical ingredient in gravitoturbulent young disks, possibly controlling their evolution, especially via their enhancement of (potentially episodic) accretion.

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Gravito-Turbulent Disks in Three Dimensions: Turbulent Velocities Versus Depth

Cited by 49 publications

References 55 publications

Gravitational Instabilities in Circumstellar Disks

Gravitational Instabilities in Circumstellar Disks

The Kennicutt–Schmidt Law and Gas Scale Height in Luminous and Ultraluminous Infrared Galaxies

Global Simulations of Self-gravitating Magnetized Protoplanetary Disks

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