Initial conditions and collapse of prestellar cores

Abstract

Prestellar Cores are created by the interaction of a turbulent velocity field and gravity. On large scales turbulence supports molecular clouds against gravity. But on small scales turbulence is able to create dense structures by locally converging flows. Eventually these structures may be captured by their own gravity and decouple from the turbulent flow. This mechanism creates the initial conditions for the formation of stellar objects. Due to the stochastic nature of turbulent velocity fields every prestellar core is unique in its shape and internal dynamics. This pecularity in the initial conditions is transformed via the collapse into an individuality of the resulting stellar systems: single stars, binaries and multiple systems. As a result, we expect the statistical features of stellar populations to be controlled by this peculiar properties of prestellar cores. I developed a method using the the typical turbulent velocity fields of molecular clouds to create prestellar cores. For the numeric simulations a 'Smoothed Particle Hydrodynamics' Code is used including a special simplified treatment for the created protostars. The hydrodynamical star formation simulation consists of three stages. The pre-collapse stage forms the prestellar cores and drives the velocity and density fields into dynamical equilibrium so that the resulting cores are physically consistent initial condition. During the collapse phase itself the contraction, fragmentation and heating of the gas is calculated. In the post-collapse phase accretion and the impact of interactions with other protostellar objects are analysed. In this way an ensemble of 22 individual simulations was analysed. The statistical characterisation of the resulting stellar population is consistent with the current observational data and yields a natural explanation for the second peak at the low mass end of the initial mass function.