Abstract
Streaming instability is a powerful mechanism which concentrates dust grains in protoplanetary discs, eventually up to the stage where they collapse gravitationally and form planetesimals. ...Previous studies inferred that it should be ineffective in viscous discs, too efficient in inviscid discs and may not operate in local pressure maxima where solids accumulate. From a linear analysis of stability, we show that streaming instability behaves differently inside local pressure maxima. Under the action of the strong differential advection imposed by the bump, a novel unstable mode develops and grows even when gas viscosity is large. Hence, pressure bumps are found to be the only places where streaming instability occurs in viscous discs. This offers a promising way to conciliate models of planet formation with recent observations of young discs.
On planet formation in HL Tau Dipierro, Giovanni; Price, Daniel; Laibe, Guillaume ...
Monthly notices of the Royal Astronomical Society. Letters,
10/2015, Letnik:
453, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We explain the axisymmetric gaps seen in recent long-baseline observations of the HL Tau protoplanetary disc with the Atacama Large Millimetre/Submillimetre Array (ALMA) as being due to the different ...response of gas and dust to embedded planets in protoplanetary discs. We perform global, three-dimensional dusty smoothed particle hydrodynamics calculations of multiple planets embedded in dust/gas discs which successfully reproduce most of the structures seen in the ALMA image. We find a best match to the observations using three embedded planets with masses of 0.2, 0.27 and 0.55 M
J in the three main gaps observed by ALMA, though there remain uncertainties in the exact planet masses from the disc model.
Is the dust-to-gas ratio constant in molecular clouds? Tricco, Terrence S.; Price, Daniel J.; Laibe, Guillaume
Monthly notices of the Royal Astronomical Society. Letters,
10/2017, Letnik:
471, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract We perform numerical simulations of dusty, supersonic turbulence in molecular clouds. We model 0.1, 1 and 10 μm sized dust grains at an initial dust-to-gas mass ratio of 1:100, solving the ...equations of combined gas and dust dynamics where the dust is coupled to the gas through a drag term. We show that, for 0.1 and 1 μm grains, the dust-to-gas ratio deviates by typically 10–20 per cent from the mean, since the stopping time of the dust due to the gas drag is short compared to the dynamical time. Contrary to previous findings, we find no evidence for orders of magnitude fluctuation in the dust-to-gas ratio for ∼0.1 μm grains. Larger, 10 μm dust grains may have dust-to-gas ratios increased by up to an order of magnitude locally. Both small (0.1 μm) and large (≳1 μm) grains trace the large-scale morphology of the gas; however, we find evidence for ‘size-sorting’ of grains, where turbulence preferentially concentrates larger grains into dense regions. Size-sorting may help to explain observations of ‘coreshine’ from dark clouds and why extinction laws differ along lines of sight through molecular clouds in the Milky Way compared to the diffuse interstellar medium.
Abstract
We aim to understand under which conditions a low-mass planet can open a gap in viscous dusty protoplanetary discs. For this purpose, we extend the theory of dust radial drift to include the ...contribution from the tides of an embedded planet and from the gas viscous forces. From this formalism, we derive (i) a grain-size–dependent criterion for dust gap opening in discs, (ii) an estimate of the location of the outer edge of the dust gap and (iii) an estimate of the minimum Stokes number above which low-mass planets are able to carve gaps that appear only in the dust disc. These analytical estimates are particularly helpful to appraise the minimum mass of a hypothetical planet carving gaps in discs observed at long wavelengths and high resolution. We validate the theory against 3D smoothed particle hydrodynamics simulations of planet–disc interaction in a broad range of dusty protoplanetary discs. We find a remarkable agreement between the theoretical model and the numerical experiments.
We model the behaviour of dust grains entrained by photoevaporation-driven winds from protoplanetary discs assuming a non-rotating, plane-parallel disc. We obtain an analytic expression for the ...maximum entrainable grain size in extreme-UV radiation-driven winds, which we demonstrate to be proportional to the mass-loss rate of the disc. When compared with our hydrodynamic simulations, the model reproduces almost all of the wind properties for the gas and dust. In typical turbulent discs, the entrained grain sizes in the wind are smaller than the theoretical maximum everywhere but the inner disc due to dust settling.
ABSTRACT
Depending on their sizes, dust grains store more or less charges, catalyse more or less chemical reactions, intercept more or less photons and stick more or less efficiently to form embryos ...of planets. Hence, the need for an accurate treatment of dust coagulation and fragmentation in numerical modelling. However, existing algorithms for solving the coagulation equation are overdiffusive in the conditions of 3D simulations. We address this challenge by developing a high-order solver based on the discontinuous Galerkin method. This algorithm conserves mass to machine precision and allows to compute accurately the growth of dust grains over several orders of magnitude in size with a very limited number of dust bins.
We aim to study the migration of growing dust grains in protoplanetary discs, where growth and migration are tightly coupled. This includes the crucial issue of the radial-drift barrier for growing ...dust grains. We therefore extend the study performed in Paper I, considering models for grain growth and grain dynamics where both the migration and growth rate depend on the grain size and the location in the disc. The parameter space of disc profiles and growth models is exhaustively explored. In doing so, interpretations for the grain motion found in numerical simulations are also provided. We find that a large number of cases is required to characterize entirely the grains radial motion, providing a large number of possible outcomes. Some of them lead dust particles to be accreted on to the central star and some of them do not. We find then that q < 1 is required for discs to retain their growing particles, where q is the exponent of the radial temperature profile
. Additionally, the initial dust-to-gas ratio has to exceed a critical value for grains to pile up efficiently, thus avoiding being accreted on to the central star. Discs are also found to retain efficiently small dust grains regenerated by fragmentation. We show how those results are sensitive to the turbulent model considered. Even though some physical processes have been neglected, this study allows us to sketch a scenario in which grains can survive the radial-drift barrier in protoplanetary discs as they grow.
ABSTRACT
Streaming instability is a privileged channel to bridge the gap between collisional growth of dust grains and planetesimal formation triggered by gravity. This instability is thought to ...develop through its secular mode, which is long-time growing and may not develop easily in real discs. We address this point by revisiting its perturbation analysis. A third-order expansion with respect to the Stokes number reveals important features overlooked so far. The secular mode can be stable. Epicycles can be unstable, more resistant to viscosity, and are identified by Green’s function analysis as promising channels for planetesimals formation.
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