Star Formation from Turbulent Fragmentation

Abstract

Star formation is intimately linked to the dynamical evolution of molecular clouds. Turbulent fragmentation determines where and when protostellar cores form, and how they contract and grow in mass via accretion from the surrounding cloud material. Efficiency, spatial distribution and timescale of star formation in turbulent clouds are estimated by comparing numerical models of self-gravitating isothermal gas where turbulence is assumed to have decayed or is driven at supersonic speed on various wavelengths. Turbulence that is not continuously replenished or that is driven on large scales leads to a rapid formation of stars in a clustered mode, whereas interstellar turbulence that carries most energy on small scales results in isolated star formation with low efficiency. Protostellar accretion rates strongly vary in time and peak at a few 10^-5 M_sun/year. The clump mass spectrum for models of pure hydrodynamic turbulence is steeper than the observed one, but becomes comparable when including gravity. The mass spectrum of dense cores, on the other hand, is log-normal for decaying and large-wavelength turbulence, similar to the IMF, but is to flat in the case of small-scale turbulence.