Dust Dynamics in Protoplanetary Disk Winds Driven by Magneto-Rotational Turbulence: A Mechanism for Floating Dust Grains with Characteristic Size (original) (raw)
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Dust distribution in protoplanetary disks
Astronomy & Astrophysics, 2005
We present the results of a three dimensional, locally isothermal, non-self-gravitating SPH code which models protoplanetary disks with two fluids: gas and dust. We ran simulations of a 1 M star surrounded by a 0.01 M disk comprising 99% gas and 1% dust in mass and extending from 0.5 to ∼300 AU. The grain size ranges from 10 −6 m to 10 m for the low resolution (∼25 000 SPH particles) simulations and from 10 −4 m to 10 cm for the high resolution (∼160 000 SPH particles) simulations. Dust grains are slowed down by the sub-Keplerian gas and lose angular momentum, forcing them to migrate towards the central star and settle to the midplane. The gas drag efficiency varies according to the grain size, with the larger bodies being weakly influenced and following marginally perturbed Keplerian orbits, while smaller grains are strongly coupled to the gas. For intermediate sized grains, the drag force decouples the dust and gas, allowing the dust to preferentially migrate radially and efficiently settle to the midplane. The resulting dust distributions for each grain size will indicate, when grain growth is added, the regions when planets are likely to form.
Monthly Notices of the Royal Astronomical Society, 2001
We investigate the response of dust particles in the mid-plane of a protoplanetary disc to the turbulent velocity field of long-lived, large-scale vortical circulation. The dynamical problem is studied through numerical integrations of the equations of motion for individual particles (the sizes of which range from centimetres to metres) subject to the solar gravity and the friction drag of the nebular gas. It is found, neglecting the thickness of the disc, that the particles do not drift inwards to the central star as occurs in a standard symmetrical nebula. Vortices tend to capture a large number of the particles. The effectiveness of this size-selective concentration mechanism depends not only on the value of the drag and the distance from the Sun, but also on the elongation of the vortex and its characteristic lifetime. Typical anticyclonic vortices with exponential decay times of 30 orbital periods and semiaxis ratios of 4 can increase the local surface density by a factor of 4 in a lifetime and accumulate 0:03±0:3 Earth masses. If the elongation is significant (.7), the vortex cannot concentrate any significant amount of solid material. Vortices with an elongation of about 2 are the most effective as regards trapping of dust. We have also found analytical expressions for the capture time as well as capture constraints as a function of the friction parameter, the elongation of the vortex and the impact parameter. By increasing the lifetime and the surface density of the solid particles, this confining mechanism can make the agglomeration of the solid material of the nebula (through collisional aggregation or gravitational instabilities) much more efficient than previously believed. This offers new possibilities for the formation of the planetesimals and the giant planet cores, and may explain the rapid formation of extrasolar giant planets.
Dust evolution in protoplanetary disk
2018
In this work we analysed some essential physics of a protoplanetary disk, then the most important models of dust dynamics are browsed, to conclude with a study of coagulative processes starting from the now classic Smoluchowski equation (1916), while following some more recent theoretical patterns and keeping an eye on order of magnitude estimates where possible. i * * * Chapter 1 Protoplanetary Disks A protoplanetary disk is the result of the collapse of a molecular cloud of gas and dust due to gravity. Under the action of the competing forces associated with gravity, gas pressure, magnetic support and rotation, the contracting nebula begins to spin faster because of angular momentum conservation, as it starts to flatten, under the effect of stronger centrifugal forces, into a spinning disk with a bulge at the center. The instabilities in the collapsing and rotating cloud cause localized gravitational collapses, and the bulge becomes the central star.
Dusty Vortices in Protoplanetary Disks
The Astrophysical Journal, 2006
Global two-dimensional simulations are used to study the coupled evolution of gas and solid particles in a Rossby unstable protoplanetary disk. The initial radial bump in density is unstable to the formation of Rossby waves, which roll up and break into anticyclonic vortices that gradually merge into a large-scale vortical structure persisting for more than 100 rotations. Conditions for the growth of such vortices may naturally appear at the outer edge of the ''dead zone'' of a protoplanetary disk where gas tends to pile up. We find that solid particles are captured by the vortices and change the evolution: (1) large particles rapidly sink toward the center of the vortices and increase the solid-togas ratio by an order of magnitude, (2) solid particles tend to reduce the lifetime of the vortices, and (3) solid particles are effectively confined in the vortices before they are dispersed by the Keplerian shear flow. These results confirm that in a minimum mass solar nebula, persistent vortices could be good places for the formation of the planetesimals or the rocky cores of gas giant planets as soon as particles reach boulder size.
Dust evolution in protoplanetary disks
Proceedings of the International Astronomical Union, 2007
We investigate the behaviour of dust in protoplanetary disks under the action of gas drag using our 3D, two-fluid (gas+dust) SPH code. We present the evolution of the dust spatial distribution in global simulations of planetless disks as well as of disks containing an already formed planet. The resulting dust structures vary strongly with particle size and planetary gaps are much sharper than in the gas phase, making them easier to detect with ALMA than anticipated. We also find that there is a range of masses where a planet can open a gap in the dust layer whereas it doesn't in the gas disk. Our dust distributions are fed to the radiative transfer code MCFOST to compute synthetic images, in order to derive constraints on the settling and growth of dust grains in observed disks.
Two-fluid Instability of Dust and Gas in the Dust Layer of a Protoplanetary Disk. ArXiv e-prints
Instabilities of the dust layer in a protoplanetary disk are investigated. It is known that the streaming instability develops and dust density concentration occurs in a situation where the initial dust density is uniform. This work considers the effect of initial dust density gradient vertical to the midplane. Dust and gas are treated as different fluids. Pressure of dust fluid is assumed to be zero. The gas friction time is assumed to be constant. Axisymmetric two-dimensional numerical simulation was performed using the spectral method. We found that an instability develops with a growth rate on the order of the Keplerian angular velocity even if the gas friction time multiplied by the Keplerian angular velocity is as small as 0.001. This instability is powered by two sources: (1) the vertical shear of the azimuthal velocity, and (2) the relative motion of dust and gas coupled with the dust density fluctuation due to advection. This instability diffuses dust by turbulent advection and the maximum dust density decreases. This means that the dust concentration by the streaming instability which is seen in the case of a uniform initial dust density becomes ineffective as dust density gradient increases by the dust settling toward the midplane.
Two-fluid instability of dust and gas in the dust layer of a protoplanetary disk
Instabilities of the dust layer in a protoplanetary disk are investigated. It is known that the streaming instability develops and dust density concentration occurs in a situation where the initial dust density is uniform. This work considers the effect of initial dust density gradient vertical to the midplane. Dust and gas are treated as different fluids. Pressure of dust fluid is assumed to be zero. The gas friction time is assumed to be constant. Axisymmetric two-dimensional numerical simulation was performed using the spectral method. We found that an instability develops with a growth rate on the order of the Keplerian angular velocity even if the gas friction time multiplied by the Keplerian angular velocity is as small as 0.001. This instability is powered by two sources: (1) the vertical shear of the azimuthal velocity, and (2) the relative motion of dust and gas coupled with the dust density fluctuation due to advection. This instability diffuses dust by turbulent advection and the maximum dust density decreases. This means that the dust concentration by the streaming instability which is seen in the case of a uniform initial dust density becomes ineffective as dust density gradient increases by the dust settling toward the midplane.
Co-evolution of dust grains and protoplanetary disks
arXiv (Cornell University), 2023
We propose a new evolutionary process of protoplanetary disks "co-evolution of dust grains and protoplanetary disks", revealed by dust-gas two-fluid non-ideal magnetohydrodynamics simulations considering the growth of dust and associated changes in magnetic resistivity. We found that the dust growth significantly affects disk evolution by changing the coupling between the gas and magnetic field. Moreover, once the dust grains sufficiently grow and the adsorption of charged particles on dust grains becomes negligible, the physical quantities (e.g., density and magnetic field) of the disk are well described by characteristic power laws. In this disk structure, the radial profile of density is steeper and the disk mass is smaller than those of the model ignoring dust growth. We analytically derive these power laws from the basic equations of non-ideal magnetohydrodynamics. The analytical power laws are determined only by observable physical quantities, e.g., central stellar mass and mass accretion rate, and do not include difficult-to-determine parameters e.g., viscous parameter α. Therefore, our model is observationally testable and this disk structure is expected to provide a new perspective for future studies on protostar and disk evolution.
An Analytical Model of Radial Dust Trapping in Protoplanetary Disks
The Astrophysical Journal
We study dust concentration in axisymmetric gas rings in protoplanetary disks. Given the gas surface density, we derived an analytical total dust surface density by taking into account the differential concentration of all the grain sizes. This model allows us to predict the local dust-togas mass ratio and the slope of the particle size distribution, as a function of radius. We test this analytical model comparing it with a 3D magneto-hydrodynamical simulation of dust evolution in an accretion disk. The model is also applied to the disk around HD 169142. By fitting the disk continuum observations simultaneously at λ = 0.87, 1.3, 3.0 mm, we obtain a global dust-togas mass ratio global = 1.05×10 −2 and a viscosity coefficient α = 1.35 × 10 −2. This model can be easily implemented in numerical simulations of accretion disks.