DYNAMICS OF SOLIDS IN THE MIDPLANE OF PROTOPLANETARY DISKS: IMPLICATIONS FOR PLANETESIMAL FORMATION

Journal Article · Wed Oct 20 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/722/2/1437· OSTI ID:21464611

Xuening, Bai

We present local two-dimensional and three-dimensional hybrid numerical simulations of particles and gas in the midplane of protoplanetary disks (PPDs) using the Athena code. The particles are coupled to gas aerodynamically, with particle-to-gas feedback included. Magnetorotational turbulence is ignored as an approximation for the dead zone of PPDs, and we ignore particle self-gravity to study the precursor of planetesimal formation. Our simulations include a wide size distribution of particles, ranging from strongly coupled particles with dimensionless stopping time {tau}{sub s} {identical_to} {Omega}t{sub stop} = 10{sup -4} (where {Omega} is the orbital frequency, t{sub stop} is the particle friction time) to marginally coupled ones with {tau}{sub s} = 1, and a wide range of solid abundances. Our main results are as follows. (1) Particles with {tau}{sub s} {approx}> 10{sup -2} actively participate in the streaming instability (SI), generate turbulence, and maintain the height of the particle layer before Kelvin-Helmholtz instability is triggered. (2) Strong particle clumping as a consequence of the SI occurs when a substantial fraction of the solids are large ({tau}{sub s} {approx}> 10{sup -2}) and when height-integrated solid-to-gas mass ratio Z is super-solar. We construct a toy model to offer an explanation. (3) The radial drift velocity is reduced relative to the conventional Nakagawa-Sekiya-Hayashi (NSH) model, especially at high Z. Small particles may drift outward. We derive a generalized NSH equilibrium solution for multiple particle species which fits our results very well. (4) Collision velocity between particles with {tau}{sub s} {approx}> 10{sup -2} is dominated by differential radial drift, and is strongly reduced at larger Z. This is also captured by the multi-species NSH solution. Various implications for planetesimal formation are discussed. In particular, we show that there exist two positive feedback loops with respect to the enrichment of local disk solid abundance and grain growth. All these effects promote planetesimal formation.

• OSTI ID: 21464611
• Journal Information: Astrophysical Journal, Vol. 722, Issue 2; Other Information: DOI: 10.1088/0004-637X/722/2/1437; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

97 MATHEMATICAL METHODS AND COMPUTING
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABUNDANCE
APPROXIMATIONS
COMPUTERIZED SIMULATION
GRAVITATION
HELMHOLTZ INSTABILITY
HYDRODYNAMICS
MATHEMATICAL SOLUTIONS
PLANETS
PROTOPLANETS
THREE-DIMENSIONAL CALCULATIONS
TURBULENCE
TWO-DIMENSIONAL CALCULATIONS
CALCULATION METHODS
FLUID MECHANICS
INSTABILITY
MECHANICS
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
SIMULATION