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Fragmentation of Molecular Clouds:
The Initial Phases of a Stellar Cluster
Using smoothed particle hydrodynamics in combination with the
special-purpose hardware device GRAPE, we numerically
investigate the initial phases of the star-formation process. We
follow the dynamical evolution and fragmentation of large regions
within molecular clouds to form a cluster of protostellar
cores. Adopting an isothermal description of self-gravitating gas, we
show that even this simple model is able to explain many of the
observed features of star-forming regions and identify the processes
that dominate the formation and evolution of protostellar cores. The
number of protostellar cores that form during the evolution is roughly
proportional to the number of Jeans masses contained in the system
initially. The overall dynamical behavior of the system is insensitive
to the adopted initial conditions, since it evolves through a sequence
of highly probabilistic events.
The interplay between self-gravity and
gas pressure creates a complex
network of clumps, sheets and filaments,
and the subsequent evolution
leads to the formation of a bound cluster
of protostellar cores.
These grow in mass via accretion from
the available gas reservoir and
are subject to highly unpredictable N-body
interactions. We find
that the angular momenta of protostellar
cores are correlated with
their location. The mass spectrum
of gas clumps can be well
approximated by a power-law distribution
dN/dM = M-1.5,
comparable to observed molecular clouds.
In contrast, the mass
spectrum of protostellar cores is best
described by a log-normal
distribution which peaks roughly at the
overall Jeans mass of the
system. With the appropriate scaling,
this is in excellent agreement
with the IMF for multiple stellar systems
and suggests a
star-formation efficiency which ranges
from 5 to 15%.
You can download the gzipped PS-file HERE and the pdf file HERE.
