Massive Star Formation

TL;DR

This chapter reviews recent progress in understanding massive star formation, emphasizing high accretion rates, their effects on stellar properties, and the transition to ultra-compact H II regions.

Contribution

It highlights the role of high accretion rates in massive star formation and discusses diagnostic tools for identifying different evolutionary phases.

Findings

High accretion rates lead to larger stellar radii and lower temperatures.

Luminous young stellar objects may not ionize surroundings due to low temperatures.

Transition to ultra-compact H II regions marks end of high accretion phase.

Abstract

This chapter reviews progress in the field of massive star formation. It focuses on evidence for accretion and current models that invoke high accretion rates. In particular it is noted that high accretion rates will cause the massive young stellar object to have a radius much larger than its eventual main sequence radius throughout much of the accretion phase. This results in low effective temperatures which may provide the explanation as to why luminous young stellar objects do not ionized their surroundings to form ultra-compact H II regions. The transition to the ultra-compact H II region phase would then be associated with the termination of the high accretion rate phase. Objects thought to be in a transition phase are discussed and diagnostic diagrams to distinguish between massive young stellar objects and ultra-compact H II regions in terms of line widths and radio luminosity are presented.