Models of the Stellar Initial Mass Function

Abstract

In the past decade, we have witnessed a paradigm shift in star formation theory away from a quasi-static picture, where magnetic fields dominate the process, towards a much more dynamic and realistic approach. We now think that the process of stellar birth is controlled by the complex interplay between self-gravity and a number of opposing physical agents, the most important of which is the supersonic turbulence ubiquitously observed in the interstellar medium. On large scales it can support clouds against contraction, while on small scales it can provoke localized collapse. Turbulence establishes a complex network of interacting shocks, where dense cores form at the stagnation points of convergent flows. Some of these fluctuations become gravitationally unstable to form stars. Stellar birth is a highly intermittent process and any theory of star formation therefore must be statistical in nature. In this short contribution we review some of the current theoretical models of stellar birth. As mass is the most important parameter determining the evolution of individual stars, our focus lies on explaining the distribution of stellar masses of birth, the so-called initial mass function. Our text is a short excerpt of a lecture given at a Saas Fee winter school in 2013.