Self-Sustaining Vortices in Protoplanetary Disks: Setting the Stage for Planetary System Formation

Abstract The core accretion scenario of planet formation assumes that planetesimals and planetary embryos are formed during the primordial, gaseous phases of the protoplanetary disk. However, how the dust particles overcome the traditional growth barriers is not well understood. Recently proposed viscous ring-instability explains the concentric rings observed in protoplanetary disks by assuming that the dust grains can reduce the gas conductivity, which can weaken the magneto-rotational instability. We present an analysis of this model with the help of GPU-based numerical hydrodynamic simulations of coupled gas and dust in the thin-disk limit. During the evolution of the disk the dusty rings become Rossby unstable and break up into a cascade of small-scale vortices. The vortices form secularly stable dusty structures, where the rapid dust growth can occur via the streaming instability. The phenomenon of self-sustaining vortices is consistent with observational constraints of exoplanets and sets a favorable environment for planetary system formation.

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Streaming instability of multiple particle species in protoplanetary disks

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832783 ◽

2018 ◽

Vol 618 ◽

pp. A75 ◽

Cited By ~ 13

Author(s):

Noemi Schaffer ◽

Chao-Chin Yang ◽

Anders Johansen

Keyword(s):

Particle Size ◽

Size Distribution ◽

Protoplanetary Disks ◽

Single Species ◽

Stokes Number ◽

Dust Particles ◽

Particle Sizes ◽

Particle Species ◽

Streaming Instability ◽

Large Particles

The radial drift and diffusion of dust particles in protoplanetary disks affect both the opacity and temperature of such disks, as well as the location and timing of planetesimal formation. In this paper, we present results of numerical simulations of particle-gas dynamics in protoplanetary disks that include dust grains with various size distributions. We have considered three scenarios in terms of particle size ranges, one where the Stokes number τs = 10−1−100, one where τs = 10−4−10−1, and finally one where τs = 10−3−100. Moreover, we considered both discrete and continuous distributions in particle size. In accordance with previous works we find in our multispecies simulations that different particle sizes interact via the gas and as a result their dynamics changes compared to the single-species case. The larger species trigger the streaming instability and create turbulence that drives the diffusion of the solid materials. We measured the radial equilibrium velocity of the system and find that the radial drift velocity of the large particles is reduced in the multispecies simulations and that the small particle species move on average outwards. We also varied the steepness of the size distribution, such that the exponent of the solid number density distribution, dN∕da ∝ a−q, is either q = 3 or q = 4. Overall, we find that the steepness of the size distribution and the discrete versus continuous approach have little impact on the results. The level of diffusion and drift rates are mainly dictated by the range of particle sizes. We measured the scale height of the particles and observe that small grains are stirred up well above the sedimented midplane layer where the large particles reside. Our measured diffusion and drift parameters can be used in coagulation models for planet formation as well as to understand relative mixing of the components of primitive meteorites (matrix, chondrules and CAIs) prior to inclusion in their parent bodies.

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The Characterization of the Dust Content in the Ring Around Sz 91: Indications of Planetesimal Formation?

The Astrophysical Journal ◽

10.3847/1538-4357/ac21d0 ◽

2021 ◽

Vol 923 (1) ◽

pp. 128

Author(s):

Karina Maucó ◽

Carlos Carrasco-González ◽

Matthias R. Schreiber ◽

Anibal Sierra ◽

Johan Olofsson ◽

...

Keyword(s):

Grain Growth ◽

Protoplanetary Disks ◽

Dust Particles ◽

Disk System ◽

Streaming Instability ◽

Multi Wavelength ◽

Pressure Bump ◽

Dust Ring ◽

Strong Agreement

Abstract One of the most important questions in the field of planet formation is how millimeter- and centimeter-sized dust particles overcome radial drift and fragmentation barriers to form kilometer-sized planetesimals. ALMA observations of protoplanetary disks, in particular transition disks or disks with clear signs of substructures, can provide new constraints on theories of grain growth and planetesimal formation, and therefore represent one possibility for progress on this issue. We here present ALMA band 4 (2.1 mm) observations of the transition disk system Sz 91, and combine them with previously obtained band 6 (1.3 mm) and band 7 (0.9 mm) observations. Sz 91, with its well-defined millimeter ring, more extended gas disk, and evidence of smaller dust particles close to the star, constitutes a clear case of dust filtering and the accumulation of millimeter-sized particles in a gas pressure bump. We compute the spectral index (nearly constant at ∼3.34), optical depth (marginally optically thick), and maximum grain size (∼0.61 mm) in the dust ring from the multi-wavelength ALMA observations, and compare the results with recently published simulations of grain growth in disk substructures. Our observational results are in strong agreement with the predictions of models for grain growth in dust rings that include fragmentation and planetesimal formation through streaming instability.

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Dust Settling and Clumping in MRI-turbulent Outer Protoplanetary Disks

The Astrophysical Journal ◽

10.3847/1538-4357/ac31a7 ◽

2022 ◽

Vol 924 (1) ◽

pp. 3

Author(s):

Ziyan Xu ◽

Xue-Ning Bai

Keyword(s):

Protoplanetary Disks ◽

Rotational Instability ◽

Local Pressure ◽

Zonal Flows ◽

Streaming Instability ◽

Numerical Studies ◽

Outer Disk ◽

External Turbulence ◽

Local Shearing ◽

Modest Level

Abstract Planetesimal formation is a crucial yet poorly understood process in planet formation. It is widely believed that planetesimal formation is the outcome of dust clumping by the streaming instability (SI). However, recent analytical and numerical studies have shown that the SI can be damped or suppressed by external turbulence, and at least the outer regions of protoplanetary disks are likely weakly turbulent due to magneto-rotational instability (MRI). We conduct high-resolution local shearing-box simulations of hybrid particle-gas magnetohydrodynamics (MHD), incorporating ambipolar diffusion as the dominant nonideal MHD effect, applicable to outer disk regions. We first show that dust backreaction enhances dust settling toward the midplane by reducing turbulence correlation time. Under modest level of MRI turbulence, we find that dust clumping is in fact easier than the conventional SI case, in the sense that the threshold of solid abundance for clumping is lower. The key to dust clumping includes dust backreaction and the presence of local pressure maxima, which in our work is formed by the MRI zonal flows overcoming background pressure gradient. Overall, our results support planetesimal formation in the MRI-turbulent outer protoplanetary disks, especially in ring-like substructures.

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Large-scale planetesimal formation by streaming instability

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313008284 ◽

2013 ◽

Vol 8 (S299) ◽

pp. 177-178

Author(s):

Chao-Chin Yang ◽

Anders Johansen

Keyword(s):

Large Scale ◽

Particle Concentration ◽

Protoplanetary Disks ◽

Current Theory ◽

Local Region ◽

Limited Size ◽

Streaming Instability ◽

Feeding Zone ◽

Almost All ◽

Core Accretion

AbstractIn current theory of planet formation, streaming instability is one of the most promising mechanisms to overcome the meter-barrier in the course of core accretion. Almost all previous works, however, were focused on a local region of protoplanetary disks with a limited size of about 0.2 gas scale heights. Only one radial filamentary particle concentration was seen in these studies. To address this, we conduct the largest-scale simulations of this kind to date, up to 0.8 gas scale heights both horizontally and vertically. We demonstrate that streaming instability remains robust on large scale and multiple radial particle concentrations exist in large enough boxes. This result may be important in characterising the feeding zone of planetesimal formation.

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Impact of the Small-Scale Spatial Distribution of Dust Particles on the Chemical Evolution of the Diffuse Interstellar Medium

Astronomy Reports ◽

10.1134/s1063772920090061 ◽

2020 ◽

Vol 64 (8) ◽

pp. 693-710

Author(s):

V. A. Sokolova ◽

A. I. Vasyunin ◽

A. B. Ostrovskii ◽

S. Yu. Parfenov

Keyword(s):

Spatial Distribution ◽

Interstellar Medium ◽

Chemical Evolution ◽

Dust Particles ◽

Small Scale

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GJ 436b and the stellar wind interaction: simulations constraints using Lyα and Hα transits

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3867 ◽

2020 ◽

Author(s):

Carolina Villarreal D’Angelo ◽

Aline A Vidotto ◽

Alejandro Esquivel ◽

Gopal Hazra ◽

Allison Youngblood

Keyword(s):

Mass Loss ◽

Stellar Wind ◽

Planetary System ◽

Neutral Hydrogen ◽

Hydrogen Atmosphere ◽

Planetary Atmosphere ◽

Hydrodynamic Simulations ◽

Stellar Disc ◽

Planetary Mass ◽

Best Fit

Abstract The GJ 436 planetary system is an extraordinary system. The Neptune-size planet that orbits the M3 dwarf revealed in the Lyα line an extended neutral hydrogen atmosphere. This material fills a comet-like tail that obscures the stellar disc for more than 10 hours after the planetary transit. Here, we carry out a series of 3D radiation hydrodynamic simulations to model the interaction of the stellar wind with the escaping planetary atmosphere. With these models, we seek to reproduce the $\sim 56\%$ absorption found in Lyα transits, simultaneously with the lack of absorption in Hα transit. Varying the stellar wind strength and the EUV stellar luminosity, we search for a set of parameters that best fit the observational data. Based on Lyα observations, we found a stellar wind velocity at the position of the planet to be around [250-460] km s−1 with a temperature of [3 − 4] × 105 K. The stellar and planetary mass loss rates are found to be 2 × 10−15 M⊙ yr−1 and ∼[6 − 10] × 109 g s−1, respectively, for a stellar EUV luminosity of [0.8 − 1.6] × 1027 erg s−1. For the parameters explored in our simulations, none of our models present any significant absorption in the Hα line in agreement with the observations.

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On the Numerical Robustness of the Streaming Instability: Particle Concentration and Gas Dynamics in Protoplanetary Disks

The Astrophysical Journal ◽

10.3847/1538-4357/aaca99 ◽

2018 ◽

Vol 862 (1) ◽

pp. 14 ◽

Cited By ~ 18

Author(s):

Rixin Li ◽

Andrew N. Youdin ◽

Jacob B. Simon

Keyword(s):

Gas Dynamics ◽

Particle Concentration ◽

Protoplanetary Disks ◽

Streaming Instability ◽

Numerical Robustness

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A Lagrangian model for dust evolution in protoplanetary disks: formation of wet and dry planetesimals at different stellar masses

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834047 ◽

2018 ◽

Vol 620 ◽

pp. A134 ◽

Cited By ~ 10

Author(s):

Djoeke Schoonenberg ◽

Chris W. Ormel ◽

Sebastiaan Krijt

Keyword(s):

Accretion Rate ◽

Protoplanetary Disks ◽

Particle Method ◽

Solid Particles ◽

Lagrangian Model ◽

Low Mass Stars ◽

Streaming Instability ◽

Mass Fluxes ◽

Gas Accretion ◽

Stellar Masses

We introduce a new Lagrangian smooth-particle method to model the growth and drift of pebbles in protoplanetary disks. The Lagrangian nature of the model makes it especially suited to following characteristics of individual (groups of) particles, such as their composition. In this work we focus on the water content of solid particles. Planetesimal formation via streaming instability is taken into account, partly based on previous results on streaming instability outside the water snowline that were presented in a recent publication. We validated our model by reproducing earlier results from the literature and apply our model to steady-state viscous gas disks (with constant gas accretion rate) around stars with different masses. We also present various other models where we explore the effects of pebble accretion, the fragmentation velocity threshold, the global metallicity of the disk, and a time-dependent gas accretion rate. We find that planetesimals preferentially form in a local annulus outside the water snowline, at early times in the lifetime of the disk (≲105 yr), when the pebble mass fluxes are high enough to trigger the streaming instability. During this first phase in the planet formation process, the snowline location hardly changes due to slow viscous evolution, and we conclude that assuming a constant gas accretion rate is justified in this first stage. The efficiency of converting the solids reservoir of the disk to planetesimals depends on the location of the water snowline. Cooler disks with a closer-in water snowline are more efficient at producing planetesimals than hotter disks where the water snowline is located further away from the star. Therefore, low-mass stars tend to form planetesimals more efficiently, but any correlation may be overshadowed by the spread in disk properties.

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