Shock interactions, turbulence, and the origin of the stellar mass
  spectrum
  Supersonic turbulence is an essential element in understanding how structure
within interstellar gas is created and shaped. In the context of star
formation, many computational studies show that the mass spectrum of density
and velocity fluctuations within dense clouds, as well as the distribution of
their angular momenta, trace their origin to the statistical and physical
properties of gas that is lashed with shock waves. In this article, we review
the observations, simulations, and theories of how turbulent-like processes can
account for structures we see in molecular clouds. We then compare traditional
ideas of supersonic turbulence with a simpler physical model involving the
effects of multiple shock waves and their interaction in the interstellar
medium. Planar intersecting shock waves produce dense filaments, and generate
vortex sheets that are essential to create the broad range of density and
velocity structure in clouds. As an example, the lower mass behaviour of the
stellar initial mass function can be traced to the tendency of a collection of
shock waves to build-up a log-normal density distribution (or column density).
Vorticity - which is essential to produce velocity structure over a very broad
range of length scales in shocked clouds - can also be generated by the passage
of curved shocks or intersecting planar shocks through such media. Two major
additional physical forces affect the structure of star forming gas - gravity
and feedback processes from young stars. Both of these can produce power-law
tails at the high mass end of the IMF.
