Gravitational Collapse in Turbulent Molecular Clouds. I. Gasdynamical Turbulence
R. S. Klessen, F. Heitsch, M. M. Mac Low;
ApJ, 2000, 535, 887
ABSTRACT:Observed molecular clouds often appear to have very low star formation efficiencies and lifetimes an order of magnitude longer than their free-fall
times.
Their support is attributed to the random supersonic motions observed in
them.
We study the support of molecular clouds against gravitational collapse
by supersonic, gasdynamical turbulence using direct numerical
simulation.
Computations with two different algorithms are compared: a particle-based,
Lagrangian method (smoothed particle hydrodynamics [SPH]) and a grid-based,
Eulerian, second-order method (ZEUS).
The effects of both algorithm and
resolution can be studied with this method.
We find that, under typical molecular
cloud conditions, global collapse can indeed be prevented, but density
enhancements caused by strong shocks nevertheless become gravitationally
unstable and collapse into dense cores and, presumably, stars.
The occurrence
and efficiency of local collapse decreases as the driving wavelength
decreases and the driving strength increases.
It appears that local collapse
can be prevented entirely only with unrealistically short wavelength
driving, but observed core formation rates can be reproduced with more
realistic driving.
At high collapse rates, cores are formed on short timescales
in coherent structures with high efficiency, while at low collapse rates
they are scattered randomly throughout the region and exhibit
considerable age spread.
We suggest that this naturally explains the observed
distinction between isolated and clustered star formation.
KEYWORDS: hydrodynamics, ism: clouds, ism: kinematics and dynamics, stars: formation, turbulence
PERSOKEY:turbulence, ,
CODE: klessen2000