Toward Understanding Massive Star Formation

TLDR

Massive star formation remains poorly understood because of large distances, high extinction, short evolutionary timescales, and a lack of observational guidance that has left theoretical models controversial. This review aims to describe the collapse of a massive molecular core and critically evaluate three competing formation scenarios—monolithic collapse, competitive accretion, and stellar collisions—while also examining observed outflows, multiplicity, clustering, the upper initial mass function, and the mass limit. The authors synthesize current observations and theoretical work by outlining the collapse process of massive cores, comparing the three formation models, and summarizing key observational signatures such as outflows, multiplicity, and clustering. They conclude that high‑mass star formation is not merely a scaled‑up version of low‑mass star formation but involves distinct mechanisms driven by stellar mass and radiation pressure that shape the dynamics.

Abstract

Although fundamental for astrophysics, the processes that produce massive stars are not well understood. Large distances, high extinction, and short timescales of critical evolutionary phases make observations of these processes challenging. Lacking good observational guidance, theoretical models have remained controversial. This review offers a basic description of the collapse of a massive molecular core and a critical discussion of the three competing concepts of massive star formation: - monolithic collapse in isolated cores - competitive accretion in a protocluster environment - stellar collisions and mergers in very dense systems We also review the observed outflows, multiplicity, and clustering properties of massive stars, the upper initial mass function and the upper mass limit. We conclude that high-mass star formation is not merely a scaled-up version of low-mass star formation with higher accretion rates, but partly a mechanism of its own, primarily owing to the role of stellar mass and radiation pressure in controlling the dynamics.