Transport and Accretion in Planet-Forming Disks

Turner, Neal J.; Fromang, Sébastien; Gammie, Charles F.; Klahr, Hubert; Lesur, Geoffroy; Wardle, Mark; Bai, Xue-Ning

doi:10.2458/azu_uapress_9780816531240-ch018

Cited by 175 publications

(201 citation statements)

References 165 publications

(250 reference statements)

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“…However, there is a strong debate in the literature about the causes of the turbulence and about the size of its magnitude (Turner et al 2014). As the drift velocity of the particles depends on the gas velocity, we investigate in this section how a change in the radial gas velocity influences particle drift through the disc.…”

Section: Dependence On the Radial Gas Velocitymentioning

confidence: 99%

Pebble-isolation mass: Scaling law and implications for the formation of super-Earths and gas giants

Bitsch

Morbidelli

Johansen

et al. 2018

A&A

280

296

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The growth of a planetary core by pebble accretion stops at the so-called pebble isolation mass, when the core generates a pressure bump that traps drifting pebbles outside its orbit. The value of the pebble isolation mass is crucial in determining the final planet mass. If the isolation mass is very low, gas accretion is protracted and the planet remains at a few Earth masses with a mainly solid composition. For higher values of the pebble isolation mass, the planet might be able to accrete gas from the protoplanetary disc and grow into a gas giant. Previous works have determined a scaling of the pebble isolation mass with cube of the disc aspect ratio. Here, we expand on previous measurements and explore the dependency of the pebble isolation mass on all relevant parameters of the protoplanetary disc. We use 3D hydrodynamical simulations to measure the pebble isolation mass and derive a simple scaling law that captures the dependence on the local disc structure and the turbulent viscosity parameter α. We find that small pebbles, coupled to the gas, with Stokes number τ f < 0.005 can drift through the partial gap at pebble isolation mass. However, as the planetary mass increases, particles must be decreasingly smaller to penetrate the pressure bump. Turbulent diffusion of particles, however, can lead to an increase of the pebble isolation mass by a factor of two, depending on the strength of the background viscosity and on the pebble size. We finally explore the implications of the new scaling law of the pebble isolation mass on the formation of planetary systems by numerically integrating the growth and migration pathways of planets in evolving protoplanetary discs. Compared to models neglecting the dependence of the pebble isolation mass on the α-viscosity, our models including this effect result in higher core masses for giant planets. These higher core masses are more similar to the core masses of the giant planets in the solar system.

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Section: Dependence On the Radial Gas Velocitymentioning

confidence: 99%

Pebble-isolation mass: Scaling law and implications for the formation of super-Earths and gas giants

Bitsch

Morbidelli

Johansen

et al. 2018

A&A

280

296

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“…This instability may be active in non-magnetized parts of protoplanetary accretion disks and is perhaps discernible in their dead zones (Turner et al 2014). Nelson et al (2013, NGU13 hereafter) and Stoll & Kley (2014) demonstrate that the instability can generate a modest amount of turbulence, with effective disk α ranging somewhere between 4 × 10 −4 and 10 −3 .…”

Section: Introductionmentioning

confidence: 99%

Linear analysis of the vertical shear instability: outstanding issues and improved solutions

Umurhan

Nelson

Gressel

2016

A&A

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Context. The vertical shear instability is one of several known mechanisms that are potentially active in the so-called dead zones of protoplanetary accretion disks. A recent analysis of the instability mechanism indicates that a subset of unstable modes shows unbounded growth -both as resolution is increased and when the nominal lid of the atmosphere is extended. This trend suggests that, possibly, the model system is ill-posed. Aims. This research note both examines the energy content of these modes and questions the legitimacy of assuming separable solutions for a problem whose linear operator is fundamentally inseparable. Methods. The reduced equations governing the instability are revisited and the generated solutions are examined using both the previously assumed separable forms and an improved non-separable solution form that is introduced in this paper. Results. Reconsidering the solutions of the reduced equations by using the separable form shows that, while the low-order body modes have converged eigenvalues and eigenfunctions (for both variations in the model atmosphere's vertical boundaries and radial numerical resolution). It is also confirmed that the corresponding high-order body modes and the surface modes indeed show unbounded growth rates. The energy contained in both the higher order body modes and surface modes diminishes precipitously due to the disk's Gaussian density profile. Most of the energy of the instability is contained in the low-order modes. An inseparable solution form is introduced to filter out the inconsequential surface modes, leaving only body modes (both low-and high-order ones). The analysis predicts a fastest growing mode with a specific radial length scale. The growth rates associated with the fundamental corrugation and breathing modes match the growth and length scales observed in previous nonlinear studies of the instability. Conclusions. Linear stability analysis of the vertical shear instability should be done assuming non-separable solutions, especially for settings involving boundaries in the radial direction. We also conclude that the surface modes are relatively inconsequential because of the little energy they contain, and are artifacts of imposing specific kinematic vertical boundary conditions in isothermals disk models.

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“…However, the physical process responsible for accretion is still debated. Although the magnetorotational instability (MRI, Balbus & Hawley 1991) provides an efficient accretion mechanism, its applicability to protoplanetary discs is questionable since these objects are very weakly ionised and might quench the MRI through various nonideal magnetohydrodynamical (MHD) processes (Turner et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Spiral-driven accretion in protoplanetary discs

Lesur

Hennebelle

Fromang

2015

A&A

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We numerically investigate the dynamics of a 2D non-magnetised protoplanetary disc surrounded by an inflow coming from an external envelope. We find that the accretion shock between the disc and the inflow is unstable, leading to the generation of largeamplitude spiral density waves. These spiral waves propagate over long distances, down to radii at least ten times smaller than the accretion shock radius. We measure spiral-driven outward angular momentum transport with 10 −4 α < 10 −2 for an inflow accretion rateṀ inf 10 −8 M yr −1 . We conclude that the interaction of the disc with its envelope leads to long-lived spiral density waves and radial angular momentum transport with rates that cannot be neglected in young non-magnetised protostellar discs.

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Transport and Accretion in Planet-Forming Disks

Cited by 175 publications

References 165 publications

Pebble-isolation mass: Scaling law and implications for the formation of super-Earths and gas giants

Pebble-isolation mass: Scaling law and implications for the formation of super-Earths and gas giants

Linear analysis of the vertical shear instability: outstanding issues and improved solutions

Spiral-driven accretion in protoplanetary discs

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