Coagulation of grains in static and collapsing protostellar clouds

Weidenschilling, S. J.; Ruzmaǐkina, T. V.

doi:10.1086/174443

Cited by 90 publications

(68 citation statements)

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“…A major difference between Weidenschilling & Ruzmaikina (1994) and our works concerns the shape of the size distribution. Whereas in our calculations the mass-peak always occurs at the high-mass end of the spectrum, in the Weidenschilling & Ruzmaikina (1994) models most of the mass stays in the smallest particles.…”

Section: Growth Characteristics and Comparison To Previous Workmentioning

confidence: 89%

“…Like our study, Weidenschilling & Ruzmaikina (1994) include fragmentation in the form of erosion and, at high energies, shattering. Their particles are characterized by a strength of Q ∼ 10 6 erg g −1 , which are, therefore, somewhat weaker than the particles of our standard model.…”

Section: Growth Characteristics and Comparison To Previous Workmentioning

confidence: 97%

“…In molecular clouds, dust coagulation has been theoretically modeled by Ossenkopf (1993) and Weidenschilling & Ruzmaikina (1994). In these studies, coagulation is driven by processes that provide grains with a relative motion.…”

Section: Introductionmentioning

confidence: 99%

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Dust coagulation and fragmentation in molecular clouds

Ormel¹,

Paszun²,

Dominik³

et al. 2009

A&A

243

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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Section: Growth Characteristics and Comparison To Previous Workmentioning

confidence: 89%

Section: Growth Characteristics and Comparison To Previous Workmentioning

confidence: 97%

See 1 more Smart Citation

Dust coagulation and fragmentation in molecular clouds

Ormel¹,

Paszun²,

Dominik³

et al. 2009

A&A

243

337

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“…The additional extinction decreases the detection rate of coreshine for distant or deeply embedded low-mass cores since it moves the ratio of coreshine intensity and background intensity towards the detection limit of the instrument. 1 We note that this does not necessarily exclude locally acting grain growth mechanisms proposed for cores (Ossenkopf 1993;Weidenschilling & Ruzmaikina 1994;Ormel et al 2011), as long as the turbulence that creates the relative motions of the grains also provides turbulent mixing to smooth out spatial gradients in n.…”

Section: Coreshine Surface Brightness Using First-order Taylor Termsmentioning

confidence: 99%

Detecting scattered light from low-mass molecular cores at 3.6μm

Steinacker

Andersen

Thi

et al. 2014

A&A

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Context. Recently discovered scattered light at 3−5 μm from low-mass cores (so-called "coreshine") reveals the presence of grains around 1 μm, which is larger than the grains found in the low-density interstellar medium. But only about half of the 100+ cores investigated so far show the effect. This prompts further studies on the origin of this detection rate. Aims. We aim to supply criteria for detecting scattered light at 3.6 μm from molecular cloud cores. Methods. From the 3D continuum radiative transfer equation, we derive the expected scattered light intensity from a core placed in an arbitrary direction seen from Earth. We use the approximation of single scattering, consider extinction up to 2nd-order Taylor approximation, and neglect spatial gradients in the dust size distribution. We analyze how scattered light can outshine the absorbing effect of extinction in front of background radiation by the core for given grain properties, anisotropic interstellar radiation field and background field. The impact of the directional characteristics of the scattering on the detection of scattered light from cores is calculated for a given grain size distribution, and local effects like additional radiation field components are discussed. The surface brightness profiles of a core with a 1D density profile are calculated for various Galactic locations, and the results are compared to the approximate detection limits. Results. We find that for optically thin radiation and a constant size distribution, a simple limit for detecting scattered light from a low-mass core can be derived that holds for grains with sizes smaller than 0.5 μm. The extinction by the core prohibits detection in bright parts of the Galactic plane, especially near the Galactic center. For scattered light received from low-mass cores with grain sizes beyond 0.5 μm, the directional characteristics of the scattering favors the detection of scattered light above and below the Galactic center, and to some extent near the Galactic anti-center. We identify the local incident radiation field as the major unknown causing deviations from this simple scheme. Conclusions. The detection of coreshine at a wavelength of 3.6 μm is a complex interplay of the incident radiation, the extinction of the background radiation, the grain properties, and the core properties like sky position and mass.

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“…Moreover, because the surface area of grains is dominated by the small end of the size distribution, the mantle thickness is very limited (<175 Å if all oxygen were to deplete as ice; Draine 1984). In terms of grain size, coagulation is the more important one of the grain growth processes (Ossenkopf 1993;Weidenschilling & Ruzmaikina 1994). At low collision velocities, small dust grains will stick upon collision forming larger conglomerates.…”

Section: Introductionmentioning

confidence: 99%

Dust coagulation and fragmentation in molecular clouds

Ormel

Min

Tielens

et al. 2011

A&A

153

180

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The dust size distribution in molecular clouds can be strongly affected by ice-mantle formation and (subsequent) grain coagulation. Following previous work where the dust size distribution has been calculated from a state-of-the art collision model for dust aggregates that involves both coagulation and fragmentation (Paper I), the corresponding opacities are presented in this study. The opacities are calculated by applying the effective medium theory assuming that the dust aggregates are a mix of 0.1 μm silicate and graphite grains and vacuum. In particular, we explore how the coagulation affects the near-IR opacities and the opacity in the 9.7 μm silicate feature. We find that as dust aggregates grow to μm-sizes both the near-IR color excess and the opacity in the 9.7 μm feature increases. Despite their coagulation, porous aggregates help to prolong the presence of the 9.7 μm feature. We find that the ratio between the opacity in the silicate feature and the near-IR color excess becomes lower with respect to the ISM, in accordance with many observations of dark clouds. However, this trend is primarily a result of ice mantle formation and the mixed material composition of the aggregates, rather than being driven by coagulation. With stronger growth, when most of the dust mass resides in particles of size ∼10 μm or larger, both the near-IR color excess and the 9.7 μm silicate feature significantly diminish. Observations at additional wavelengths, in particular in the sub-mm range, are essential to provide quantitative constraints on the dust size distribution within dense cores. Our results indicate that the sub-mm index β will increase appreciably, if aggregates grow to ∼100 μm in size.

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Coagulation of grains in static and collapsing protostellar clouds

Cited by 90 publications

References 0 publications

Dust coagulation and fragmentation in molecular clouds

Dust coagulation and fragmentation in molecular clouds

Detecting scattered light from low-mass molecular cores at 3.6μm

Dust coagulation and fragmentation in molecular clouds

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