scholarly journals Coagulation Instability in Protoplanetary Disks: A Novel Mechanism Connecting Collisional Growth and Hydrodynamical Clumping of Dust Particles

2021 ◽  
Vol 923 (1) ◽  
pp. 34
Author(s):  
Ryosuke T. Tominaga ◽  
Shu-ichiro Inutsuka ◽  
Hiroshi Kobayashi
Keyword(s):  
Gravitational Instability ◽  
Dust Particles ◽  
Mass Ratio ◽  
Dust Density ◽  
Streaming Instability ◽  
Resultant Velocity ◽  
Density Perturbations ◽  
Disk Evolution ◽  
Dust Diffusion ◽  
Orbital Periods

Abstract We present a new instability driven by a combination of coagulation and radial drift of dust particles. We refer to this instability as “coagulation instability” and regard it as a promising mechanism to concentrate dust particles and assist planetesimal formation in the very early stages of disk evolution. Because of dust-density dependence of collisional coagulation efficiency, dust particles efficiently (inefficiently) grow in a region of positive (negative) dust density perturbations, leading to a small radial variation of dust sizes and as a result radial velocity perturbations. The resultant velocity perturbations lead to dust concentration and amplify dust density perturbations. This positive feedback makes a disk unstable. The growth timescale of coagulation instability is a few tens of orbital periods even when dust-to-gas mass ratio is on the order of 10−3. In a protoplanetary disk, radial drift and coagulation of dust particles tend to result in dust depletion. The present instability locally concentrates dust particles even in such a dust-depleted region. The resulting concentration provides preferable sites for dust–gas instabilities to develop, which leads to further concentration. Dust diffusion and aerodynamical feedback tend to stabilize short-wavelength modes, but do not completely suppress the growth of coagulation instability. Therefore, coagulation instability is expected to play an important role in setting up the next stage for other instabilities, such as streaming instability or secular gravitational instability, to further develop toward planetesimal formation.

scholarly journals On the non-axisymmetric fragmentation of rings generated by the Secular Gravitational Instability

2021 ◽  
Author(s):  
Arnaud Pierens
Keyword(s):  
Growth Rate ◽  
Growth Rates ◽  
Linear Growth ◽  
Gravitational Instability ◽  
Dust Particles ◽  
Linear Growth Rate ◽  
Stability Parameters ◽  
Dust Density ◽  
Linear Evolution ◽  
Non Linear

Abstract Ringed structures have been observed in a variety of protoplanetary discs. Among the processes that might be able to generate such features, the Secular Gravitational Instability (SGI) is a possible candidate. It has also been proposed that the SGI might lead to the formation of planetesimals during the non-linear phase of the instability. In this context, we employ two-fluid hydrodynamical simulations with self-gravity to study the non-axisymmetric, non-linear evolution of ringed perturbations that grow under the action of the SGI. We find that the non-linear evolution outcome of the SGI depends mainly on the initial linear growth rate. For SGI growth rates smaller than typically σ ≳ 10−4 − 10−5Ω, dissipation resulting from dust feedback introduces a m = 1 spiral wave in the gas, even for Toomre gas stability parameters Qg > 2 for which non-axisymmetric instabilities appear in a purely gaseous disc. This one-armed spiral subsequently traps dust particles until a dust-to-gas ratio ε ∼ 1 is achieved. For higher linear growth rates, the dust ring is found to undergo gravitational collapse until the bump in the surface density profile becomes strong enough to trigger the formation of dusty vortices through the Rossby Wave Instability (RWI). Enhancements in dust density resulting from this process are found to scale with the linear growth rate, and can be such that the dust density is higher than the Roche density, leading to the formation of bound clumps. Fragmentation of axisymmetric rings produced by the SGI might therefore appear as a possible process for the formation of planetesimals.

scholarly journals CO-driven activity constrains the origin of comets

2020 ◽  
Vol 636 ◽  
pp. L3 ◽  
Author(s):  
M. Fulle ◽  
J. Blum ◽  
A. Rotundi
Keyword(s):  
Loss Rate ◽  
Dust Particles ◽  
Mass Ratio ◽  
Cometary Nuclei ◽  
Nucleus Surface ◽  
Activity Onset ◽  
Gas Loss ◽  
Open Question ◽  
Comet 67P ◽  
Co Gas

Context. An open question in the study of comets is the so-called cohesion bottleneck, that is, how dust particles detach from the nucleus. Aims. We test whether the CO pressure buildup inside the pebbles of which cometary nuclei consist can overcome this cohesion bottleneck. Methods. A recently developed pebble-diffusion model was applied here to comet C/2017K2 PANSTARRS, assuming a CO-driven activity. Results. (i) The CO-gas pressure inside the pebbles erodes the nucleus into the observed dust, which is composed of refractories, H2O ice and CO2 ice. (ii) The CO-driven activity onset occurs up to heliocentric distances of 85 au, depending on the spin orientation of the comet nucleus. (iii) The activity onset observed at ≈26 au suggests a low obliquity of the nucleus spin axis with activity in a polar summer. (iv) At 14 au, the smallest size of the ejected dust is ≈0.1 mm, consistent with observations. (v) The observed dust-loss rate of ≈200 kg s−1 implies a fallout ≥30%, a nucleus surface active area ≥10 km2, a CO-gas loss rate ≥10 kg s−1, and a dust-to-gas ratio ≤20. (vi) The CO-driven activity never stops if the average refractory-to-all-ices mass ratio in the nucleus is ≤4.5 for a nucleus all-ices-to-CO mass ratio ≈4, as observed in comets Hale–Bopp and Hyakutake. These results make comet C/2017K2 similar to the Rosetta target comet 67P/Churyumov–Gerasimenko. (vii) The erosion lifetime of cometary planetesimals is a factor 103 shorter than the timescale of catastrophic collisions. This means that the comets we observe today cannot be products of catastrophic collisions.

scholarly journals Streaming instability of multiple particle species in protoplanetary disks

2018 ◽  
Vol 618 ◽  
pp. A75 ◽  
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.

scholarly journals The Evolutionary Status of the Secondaries of Cataclysmic Binaries

1983 ◽  
Vol 72 ◽  
pp. 257-262
Author(s):  
H. Ritter
Keyword(s):  
Probability Distribution ◽  
Main Sequence ◽  
The Other ◽  
Initial Mass ◽  
Evolutionary Status ◽  
Mass Ratio ◽  
Main Sequence Stars ◽  
Cataclysmic Binaries ◽  
Low Mass ◽  
Orbital Periods

ABSTRACTIt is shown that the secondary components of cataclysmic binaries with orbital periods of less than ~10 hours are indistinguishable from ordinary low-mass main-sequence stars and that, therefore, they are essentially unevolved. On the other hand, it is shown that, depending on the mass ratio of the progenitor system, the secondary of a cataclysmic binary could be significantly evolved. The fact that nevertheless most of the observed secondaries are essentially unevolved can be accounted for by assuming that the probability distribution for the initial mass ratio is not strongly peaked towards unity mass ratio.

scholarly journals Linear analysis of the non-axisymmetric secular gravitational instability

2019 ◽  
Vol 487 (4) ◽  
pp. 5405-5415
Author(s):  
Mohsen Shadmehri ◽  
Razieh Oudi ◽  
Gohar Rastegarzadeh
Keyword(s):  
Amplification Factor ◽  
Gravitational Instability ◽  
Radial Distance ◽  
Dust Particles ◽  
Linear Perturbation ◽  
Model Parameters ◽  
Time Interval ◽  
Continuous Growth ◽  
Two Fluid ◽  
Axisymmetric Perturbations

Abstract In protoplanetary discs (PPDs) consisting of gas and dust particles, fluid instabilities induced by the drag force, including secular gravitational instability (SGI), can facilitate planet formation. Although SGI subject to the axisymmetric perturbations was originally studied in the absence of gas feedback and it then generalized using a two-fluid approach, the fate of the non-axisymmetric SGI, in either case, is an unexplored problem. We present a linear perturbation analysis of the non-axisymmetric SGI in a PPD by implementing a two-fluid model. We explore the growth of the local, non-axisymmetric perturbations using a set of linearized perturbation equations in a sheared frame. The non-axisymmetric perturbations display a significant growth during a finite time interval even when the system is stable against the axisymmetric perturbations. Furthermore, the surface density perturbations do not show the continuous growth but are temporally amplified. We also study cases where the dust component undergoes amplification whereas the gas component remains stable. The amplitude amplification, however, strongly depends on the model parameters. In the minimum mass solar nebula (MMSN), for instance, the dust fluid amplification at the radial distance 100 au occurs when the Stokes number is about unity. But the amplification factor reduces as the dust and gas coupling becomes weaker. Furthermore, perturbations with a larger azimuthal wavelength exhibit a larger amplification factor.

Ion transport in electrode sheath with non-uniform dusts

2002 ◽  
Vol 68 (4) ◽  
pp. 249-255
Author(s):  
A. P. SUN ◽  
X. M. QIU ◽  
H. H. TONG ◽  
Q. C. CHEN
Keyword(s):  
Ion Transport ◽  
Dust Particles ◽  
Uniform Density ◽  
Key Factors ◽  
Ion Density ◽  
Factors Affecting ◽  
Dust Density ◽  
Dust Charge ◽  
The Monte Carlo Method ◽  
Electrode Sheath

The Monte Carlo method is used to simulate ion transport in an Ar plasma electrode sheath with a non-uniform dust. Charge exchange and elastic collisions between ions and neutral atoms and also the collection and Coulomb scattering of ions on the dust particles are examined during the motion of ions in the sheath. In order to study the effect of the non-uniform dust density and size on ion transport, we choose an exponent dust density distribution with a uniform dust size and a normal dust radius distribution with a uniform density and compare the simulation results with those for a uniform dust. It is found that both a non-uniform and a uniform dust density affect the ion density arriving at the electrode significantly and to the same degree. At the same time, it is also found that a non-uniform and uniform dust size influence the ion density arriving at the electrode greatly, but with a slight difference. Therefore, although the dust content is very low in most processing plasmas, its influence becomes evident whether its content is uniform or non-uniform in content and size. So, we can come to the conclusion that the key factors affecting the influence of dust particles on plasma behaviour are the linear density and the average radius of dust particles rather than their distribution.

scholarly journals Dusty clumps in circumbinary discs

2019 ◽  
Vol 489 (2) ◽  
pp. 2204-2215 ◽  
Author(s):  
Pedro P Poblete ◽  
Nicolás Cuello ◽  
Jorge Cuadra
Keyword(s):  
Binary System ◽  
Gas Dynamics ◽  
Dust Particles ◽  
Feature Location ◽  
Complex Interplay ◽  
Orbital Parameters ◽  
Orbital Periods ◽  
Azimuthal Asymmetries ◽  
Two Fluid ◽  
Protoplanetary Discs

ABSTRACT Recent observations have revealed that protoplanetary discs often exhibit cavities and azimuthal asymmetries such as dust traps and clumps. The presence of a stellar binary system in the inner disc regions has been proposed to explain the formation of these structures. Here, we study the dust and gas dynamics in circumbinary discs around eccentric and inclined binaries. This is done through two-fluid simulations of circumbinary discs, considering different values of the binary eccentricity and inclination. We find that two kinds of dust structures can form in the disc: a single horseshoe-shaped clump, on top of a similar gaseous over-density; or numerous clumps, distributed along the inner disc rim. The latter features form through the complex interplay between the dust particles and the gaseous spirals caused by the binary. All these clumps survive between one and several tens of orbital periods at the feature location. We show that their evolution strongly depends on the gas–dust coupling and the binary parameters. Interestingly, these asymmetric features could in principle be used to infer or constrain the orbital parameters of a stellar companion – potentially unseen – inside the inner disc cavity. Finally, we apply our findings to the disc around AB Aurigae.

scholarly journals Long Dust Trails of Short Period Comets

1991 ◽  
Vol 126 ◽  
pp. 229-234
Author(s):  
H.U. Keller ◽  
K. Richter
Keyword(s):  
Radiation Pressure ◽  
Dust Cloud ◽  
Dust Particles ◽  
Pressure Force ◽  
Meteor Streams ◽  
Short Period ◽  
Orbital Periods ◽  
Comet Halley ◽  
Observational Techniques ◽  
Radiation Pressure Force

Comets constitute an important source for the zodiacal dust cloud. Mainly large particles are contributed because the smaller particles are emitted into hyperbolic orbits relative to the sun. Radiation pressure force reduces the effective solar gravitational attraction. Information about large cometary particles can be derived from a variety of sources requiring quite different observational techniques. Many distinct meteor streams are connected to orbits of short period comets. These streams contain large dust particles that are very little influenced by radiation pressure force. In some cases such as the η Aquarids and Orionids connected to comet Halley the total mass and the age of the meteors have been derived (Hughes, 1987; Hajduk, 1987). The mass of the streams is 5 to 10 times larger than the present mass of the nucleus and their lifetime corresponds to 2000 to 3000 orbital periods. Visible meteors are typically 10−2g and more of centimetre size.

Magnetoacoustic modes in a magnetized dusty plasma

1995 ◽  
Vol 53 (3) ◽  
pp. 317-334 ◽  
Author(s):  
N. N. Rao
Keyword(s):  
Acoustic Wave ◽  
Dusty Plasma ◽  
Acoustic Waves ◽  
Acoustic Mode ◽  
Dust Particles ◽  
Ion Acoustic Wave ◽  
Magnetized Dusty Plasma ◽  
Magnetoacoustic Waves ◽  
Component Plasma ◽  
Density Perturbations

The existence of various types of (fast) magnetoacoustic modes in different frequency regimes in a magnetized dusty plasma consisting of electrons, ions and dust particles is investigated. The analysis is carried out using an effective two-fluid MHD-like model which allows for the non-frozen motion of the component fluids. For frequencies much smaller than the dust particle gyro- frequency, we obtain a magnetoacoustic mode that is a generalization of the usual compressional fast hydromagnetic wave in an electron—ion plasma. In the higher-frequency regimes, we show the existence of two new types of modes called ‘Dust-magnetoacoustic waves’. Both modes are accompanied by compressional magnetic field and plasma number density perturbations, and are the electromagnetic generalizations of the dust-acoustic waves in an unmagnetized dusty plasma with thermal electrons and ions. For a two- component plasma, all three modes degenerate into the same fast magneto- acoustic wave found in the usual electron—ion plasmas. We also obtain another novel type of magneto-acoustic mode called a ‘dust—ion-magneto- acoustic wave’, which is an electromagnetic generalization of the dust—ion- acoustic wave. The dispersion relations as well as the frequency regimes for the existence of the various modes are explicitly obtained. An alternative derivation of the relevant governing equations using an approach similar to that employed in so-called ‘electron magnetohydrodynamics’ (EMHD) is also presented.

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