Cluster Formation in Contracting Molecular Clouds

TL;DR

This paper presents a semi-analytic model of molecular cloud contraction leading to dense cluster formation, highlighting the transition to rapid massive star production and reproducing observed star formation rates in the Orion Nebula Cluster.

Contribution

It introduces a simplified model linking cloud contraction dynamics to star formation, including an empirical law for low-mass star formation and application to real clusters.

Findings

Cloud contracts slowly until a density spike triggers instability.

Approximately 10% of cloud mass forms low-mass stars before instability.

Model reproduces observed star formation efficiency and acceleration in Orion.

Abstract

We explore, through a simplified, semi-analytic model, the formation of dense clusters containing massive stars. The parent cloud spawning the cluster is represented as an isothermal sphere. This sphere is in near force balance between self-gravity and turbulent pressure. Self-gravity, mediated by turbulent dissipation, drives slow contraction of the cloud, eventually leading to a sharp central spike in density and the onset of dynamical instability. We suggest that, in a real cloud, this transition marks the late and rapid production of massive stars. We also offer an empirical prescription, akin to the Schmidt law, for low-mass star formation in our contracting cloud. Applying this prescription to the Orion Nebula Cluster, we are able to reproduce the accelerating star formation previously inferred from the distribution of member stars in the HR diagram. The cloud turns about 10 percent of its mass into low-mass stars before becoming dynamically unstable. Over a cloud free-fall time, this figure drops to 1 percent, consistent with the overall star formation efficiency of molecular clouds in the Galaxy.