Dust coagulation in dense molecular clouds: The formation of fluffy aggregates

Details Dust coagulation in dense molecular clouds: The formation of fluffy aggregates Dust coagulation in dense molecular clouds: The formation of fluffy aggregates

Dec 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...280..617o&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 280, no. 2, p. 617-646

Computer Science

Numerical Analysis

159

Agglomeration, Coagulation, Cosmic Dust, Extinction, Interstellar Matter, Mathematical Models, Molecular Clouds, Numerical Analysis, Electric Charge, Gas Dynamics, Gravitation, Kinematics, Thermodynamic Properties, Turbulence Effects, Velocity Measurement

Scientific paper

We set up a detailed model for the dust coagulation process in dense cores of molecular clouds without beginning star formation. We took into account the effects of thermal, turbulent, gravitational motion, motion from incidential particle asymmetries, grain rotation, charges, and the accretion of molecules onto the particles. For the first time, we explicitly considered the irregularity and changing fluffiness of the clusters produced in the coagulation process. The basis for this treatment was an independent numerical simulation of the structure of such aggregates. We fitted the structure parameters by analytic functions which were used in the final model for the coagulation of the interstellar particles. With this model we carried out numerous simulations of the evolution of dust grain distributions in dense cores. Different gas densities, clump models, accretion rates, and initial grain size distributions were investigated. It was found that the main force driving the aggregation of dust particles in dense clumps is turbulence at gas densities below 108 H-atoms/cu cm and Brownian motion at higher densities. The total opacity of the resulting distributions of fluffy dust agglomerates was calculated using effective-medium theories combined with a core-mantle model for the aggregate particles. The far infrared absorptivity is enhanced by the factor 3 (at 200 micrometers) in the first steps of the coagulation process and hardly influenced by the further coagulation. For gas densities between 106 and 109/cu cm and timescales below 105 yrs, the coagulation process is efficient in changing the optical properties of the dust particles but not in the production of large heavy particles.

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