The Formation of Stellar Clusters: Time-Varying Protostellar Accretion Rates

Abstract

Identifying the processes that determine strength, duration, and variability of protostellar mass growth is a fundamental ingredient of any theory of star formation. I discuss protostellar mass accretion rates from numerical ˙ M models that follow molecular cloud evolution from turbulent fragmentation toward the formation of stellar clusters. In a dense cluster environment, is strongly time varying and influenced by the mutual interaction of protostellar ˙ M cores and their competition for accretion from the common cluster gas reservoir. Even for protostars with similar final mass, the accretion histories may differ dramatically. High-mass stars build up in the central parts of dense, cluster-forming cloud regions. They begin to form in the early phases of cluster evolution and continue to grow at a high rate until the available gas is exhausted or expelled by feedback. Lower mass stars tend to form at later phases, and declines rapidly after a short initial phase of strong growth. I present a simple fit formula for the ˙ M time evolution of the average for protostars of different masses in a dense cluster environment.