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Coagulation of grains in static and collapsing protostellar cloudsWe simulate collisional evolution of grains in dense turbulent molecular cloud cores (or Bok globules) in static equilibrium and free-fall collapse, assuming spherical symmetry. Relative velocities are due to thermal motions, differential settling, and turbulence, with the latter dominant for sonic turbulence with an assumed Kolmogorov spectrum. Realistic criteria are used to determine outcomes of collisions (coagulation vs. destruction) as functions of particle size and velocity. Results are presented for a variety of cloud parameters (radial density profile, turbulent velocity) and particle properties (density, impact strength). Results are sensitive to the assumed mechanical properties (density and impact strength) of grain aggregates. Particle growth is enhanced if aggregates have low density or fractal structures. On a timescale of a few Myr, an initial population of 0.1 micrometers grains may produce dense compact particles approximately 1 micrometer in size, or fluffy aggregates approximately 100 micrometers. For impact strengths less than or equal to 10(exp 6) ergs/g, a steady state is reached between coagulation of small grains and collisional disruption of larger aggregates. Formation of macroscopic aggregates requires high mechanical strengths and low aggregate densities. We assume sonic turbulence during collapse, with varied eddy size scales determining the dissipation rate or turbulence strength. The degree of collisional evolution during collapse is sensitive to the assumed small-scale structure (inner sc ale) of the turbulence. Weak turbulence results in few collisions and preserves the precollapse particle size distribution with little change. Strong turbulence tends to produce net destruction, rather than particle growth, during infall, unless inpact strengths are greater than 10(exp 6)ergs/g.
Document ID
19950029313
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Weidenschilling, S. J.
(Planetary Science Inst. Tucson, AZ, United States)
Ruzmaikina, T. V.
(Univ. of Arizona, Tucson, AZ United States)
Date Acquired
August 16, 2013
Publication Date
August 1, 1994
Publication Information
Publication: The Astrophysical Journal
Volume: 430
Issue: 2 pt
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A60912
Funding Number(s)
CONTRACT_GRANT: PSI-307
CONTRACT_GRANT: NASW-4616
Distribution Limits
Public
Copyright
Other

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