The role of turbulence in high-mass star formation: Subsonic and transonic turbulence are ubiquitously found at early stages

TL;DR

This study reveals that subsonic and transonic turbulence are common in early-stage massive star-forming regions, challenging the traditional view that supersonic turbulence dominates and highlighting the need for alternative support mechanisms.

Contribution

The paper provides high-resolution observations showing prevalent sub- and transonic turbulence in massive star-forming cores, suggesting turbulence alone is insufficient for star formation support.

Findings

Sub- and transonic turbulence found in 21 of 32 cores.

Cold, dense cores often located at the centers of multi-core systems.

Results support the hub-filament model for star formation distribution.

Abstract

Context. Traditionally, supersonic turbulence is considered to be one of the most likely mechanisms to slow down the gravitational collapse in dense clumps, thereby enabling the formation of massive stars. However, several recent studies have raised differing points of view based on observations carried out with sufficiently high spatial and spectral resolution. These studies call for a re-evaluation of the role turbulence plays in massive star-forming regions. Aims. Our aim is to study the gas properties, especially the turbulence, in a sample of massive star-forming regions with sufficient spatial and spectral resolution, which can both resolve the core fragmentation and the thermal line width. Methods. We observed NH3 metastable lines with the Very Large Array (VLA) to assess the intrinsic turbulence. Results. Analysis of the turbulence distribution histogram for 32 identified NH3 cores reveals the presence of three distinct components. Furthermore, our results suggest that (1) sub- and transonic turbulence is a prevalent (21 of 32) feature of massive star-forming regions and those cold regions are at early evolutionary stage. This investigation indicates that turbulence alone is insufficient to provide the necessary internal pressure required for massive star formation, necessitating further exploration of alternative candidates; and (2) studies of seven multi-core systems indicate that the cores within each system mainly share similar gas properties and masses. However, two of the systems are characterized by the presence of exceptionally cold and dense cores that are situated at the spatial center of each system. Our findings support the hub-filament model as an explanation for this observed distribution