Magnetic Aggregation: Dynamics and Numerical Modeling

Dominik, C.; Nübold, Henrik

doi:10.1006/icar.2002.6813

Cited by 63 publications

(48 citation statements)

References 45 publications

(63 reference statements)

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“…It is generally assumed that in the dense regions of protoplanetary disks not too close to the central star, electrostatic charges and magnetic materials do not play a dominant role in the interaction between grains, however, this is currently debated and several studies have investigated their effects on grain evolution in disks (Dominik and Nübold, 2002;Matthews et al, 2012;Okuzumi et al, 2011b). In the absence of these effects, dust grains in contact still possess an adhesive (van der Waals) force (Heim et al, 1999;Gundlach et al, 2011).…”

Section: Why Do Dust Particles or Dust Aggregates Grow?mentioning

confidence: 99%

Dust Evolution in Protoplanetary Disks

Testi¹,

Birnstiel²,

Ricci³

et al. 2014

Protostars and Planets VI

292

271

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In the core accretion scenario for the formation of planetary rocky cores, the first step toward planet formation is the growth of dust grains into larger and larger aggregates and eventually planetesimals. Although dust grains are thought to grow from the submicron sizes typical of interstellar dust to micron size particles in the dense regions of molecular clouds and cores, the growth from micron size particles to pebbles and kilometre size bodies must occur in the high densities reached in the mid-plane of protoplanetary disks. This critical step in the formation of planetary systems is the last stage of solids evolution that can be observed directly in young extrasolar systems before the appearance of large planetary-size bodies.Tracing the properties of dust in the disk mid-plane, where the bulk of the material for planet formation resides, requires sensitive observations at long wavelengths (sub-mm through cm waves). At these wavelengths, the observed emission can be related to the dust opacity, which in turns depend on to the grain size distribution. In recent years the upgrade of the existing (sub-)mm arrays, the start of ALMA Early Science operations and the upgrade of the VLA have significantly improved the observational constraints on models of dust evolution in protoplanetary disks. Laboratory experiments and numerical simulations led to a substantial improvement in the understanding of the physical processes of grain-grain collisions, which are the foundation for the models of dust evolution in disks.In this chapter we review the constraints on the physics of grain-grain collisions as they have emerged from laboratory experiments and numerical computations. We then review the current theoretical understanding of the global processes governing the evolution of solids in protoplanetary disks, including dust settling, growth, and radial transport. The predicted observational signatures of these processes are summarized.We discuss the recent developments in the study of grain growth in molecular cloud cores and in collapsing envelopes of protostars as these likely provide the initial conditions for the dust in protoplanetary disks. We then discuss the current observational evidence for the growth of grains in young protoplanetary disks from millimeter surveys, as well as the very recent evidence of radial variations of the dust properties in disks. We also include a brief discussion of the constraints on the small end of the grain size distribution and on dust settling as derived from optical, near-, and mid-IR observations. The observations are discussed in the context of global dust evolution models, in particular we focus on the emerging evidence for a very efficient early growth of grains in disks and the radial distribution of maximum grain sizes as the result of growth barriers in disks. We will also highlight the limits of the current models of dust evolution in disks including the need to slow the radial drift of grains to overcome the migration/fragmentation barrier.

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Section: Why Do Dust Particles or Dust Aggregates Grow?mentioning

confidence: 99%

Dust Evolution in Protoplanetary Disks

Testi¹,

Birnstiel²,

Ricci³

et al. 2014

Protostars and Planets VI

292

271

View full text Add to dashboard Cite

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“…Collisions between aggregates are modeled using the soft aggregates numerical dynamics (SAND) code (Dominik & Nübold 2002;Paszun & Dominik 2008). This code treats interactions between individual grains held together by surface forces in a contact area (Johnson et al 1971;Derjaguin et al 1975).…”

Section: B1 Collision Setup and Input Parametersmentioning

confidence: 99%

Dust coagulation and fragmentation in molecular clouds

Ormel¹,

Paszun²,

Dominik³

et al. 2009

A&A

248

337

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The cores in molecular clouds are the densest and coldest regions of the interstellar medium (ISM). In these regions ISM-dust grains have the potential to coagulate. This study investigates the collisional evolution of the dust population by combining two models: a binary model that simulates the collision between two aggregates and a coagulation model that computes the dust size distribution with time. In the first, results from a parameter study quantify the outcome of the collision -sticking, fragmentation (shattering, breakage, and erosion) -and the effects on the internal structure of the particles in tabular format. These tables are then used as input for the dust evolution model, which is applied to an homogeneous and static cloud of temperature 10 K and gas densities between 10 3 and 10 7 cm −3 . The coagulation is followed locally on timescales of ∼10 7 yr. We find that the growth can be divided into two stages: a growth dominated phase and a fragmentation dominated phase. Initially, the mass distribution is relatively narrow and shifts to larger sizes with time. At a certain point, dependent on the material properties of the grains as well as on the gas density, collision velocities will become sufficiently energetic to fragment particles, halting the growth and replenishing particles of lower mass. Eventually, a steady state is reached, where the mass distribution is characterized by a mass spectrum of approximately equal amount of mass per logarithmic size bin. The amount of growth that is achieved depends on the cloud's lifetime. If clouds exist on free-fall timescales the effects of coagulation on the dust size distribution are very minor. On the other hand, if clouds have long-term support mechanisms, the impact of coagulation is important, resulting in a significant decrease of the opacity on timescales longer than the initial collision timescale between big grains.

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“…The contact model used in this work is similar to the one developed in granular physics [7][8][9][10][11], which is able to capture aggregates maintaining their structures under low stress while being restructured under high stress. The bond strength is assumed to be sufficiently larger than the thermal energy k B T , therefore Brownian forces are not considered.…”

Section: Introductionmentioning

confidence: 99%

Restructuring of colloidal aggregates in shear flow

et al. 2012

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Abstract. A method to couple interparticle contact models with Stokesian dynamics (SD) is introduced to simulate colloidal aggregates under flow conditions. The contact model mimics both the elastic and plastic behavior of the cohesive connections between particles within clusters. Owing to this, clusters can maintain their structures under low stress while restructuring or even breakage may occur under sufficiently high stress conditions. SD is an efficient method to deal with the long-ranged and many-body nature of hydrodynamic interactions for low Reynolds number flows. By using such a coupled model, the restructuring of colloidal aggregates under shear flows with stepwise increasing shear rates was studied. Irreversible compaction occurs due to the increase of hydrodynamic stress on clusters. Results show that the greater part of the fractal clusters are compacted to rod-shaped packed structures, while the others show isotropic compaction.

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Magnetic Aggregation: Dynamics and Numerical Modeling

Cited by 63 publications

References 45 publications

Dust Evolution in Protoplanetary Disks

Dust Evolution in Protoplanetary Disks

Dust coagulation and fragmentation in molecular clouds

Restructuring of colloidal aggregates in shear flow

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