| Issue |
A&A
Volume 502, Number 1, July IV 2009
|
|
|---|---|---|
| Page(s) | 385 - 389 | |
| Section | Planets and planetary systems | |
| DOI | https://doi.org/10.1051/0004-6361/200911865 | |
| Published online | 15 June 2009 | |
Research Note
On the pressure of collisionless particle fluids
The case of solids settling in disks
1
Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux (LAB), 2 rue de l'Observatoire, BP 89, 33271 Floirac Cedex, France
2
CNRS/INSU - UMR5804, BP 89, 33271 Floirac Cedex, France e-mail: Franck.Hersant@obs.u-bordeaux1.fr
Received:
17
February
2009
Accepted:
4
May
2009
Aims. Collections of dust, grains, and planetesimals are often treated as a pressureless fluid. We study the validity of neglecting the pressure of such a fluid by computing it exactly for the case of particles settling in a disk.
Methods. We solve a modified collisionless Boltzmann equation for the particles and compute the corresponding moments of the phase space distribution: density, momentum, and pressure.
Results. We find that whenever the Stokes number, defined as the ratio of the gas drag timescale to the orbital
timescale, is more than 
, the particle fluid cannot be considered as pressureless. While we show it
only in the simple case of particles settling in a laminar disk, this property is likely to remain true for most flows,
including turbulent flows.
Key words: hydrodynamics / methods: analytical / planetary systems: formation
© ESO, 2009
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