Radiation hydrodynamics of triggered star formation: the effect of the diffuse radiation field

TL;DR

This study models the impact of diffuse radiation fields on triggered star formation, revealing significant effects on collapse dynamics, shock strength, and the formation of structures like elephant trunks, with implications for understanding star formation processes.

Contribution

It introduces a combined Monte Carlo and hydrodynamics simulation approach to include diffuse radiation effects in star formation models, highlighting their influence on collapse and structure formation.

Findings

Diffuse field significantly alters collapse timescales.

Stronger shocks lead to increased shell density and photo-evaporative ejections.

Diffuse field inclusion affects the formation and evolution of elephant trunks.

Abstract

We investigate the effect of including diffuse field radiation when modelling the radiatively driven implosion of a Bonnor-Ebert sphere (BES). Radiation-hydrodynamical calculations are performed by using operator splitting to combine Monte Carlo photoionization with grid-based Eulerian hydrodynamics that includes self-gravity. It is found that the diffuse field has a significant effect on the nature of radiatively driven collapse which is strongly coupled to the strength of the driving shock that is established before impacting the BES. This can result in either slower or more rapid star formation than expected using the on-the-spot approximation depending on the distance of the BES from the source object. As well as directly compressing the BES, stronger shocks increase the thickness and density in the shell of accumulated material, which leads to short, strong, photo-evaporative ejections that reinforce the compression whenever it slows. This happens particularly effectively when the diffuse field is included as rocket motion is induced over a larger area of the shell surface. The formation and evolution of 'elephant trunks' via instability is also found to vary significantly when the diffuse field is included. Since the perturbations that seed instabilities are smeared out elephant trunks form less readily and, once formed, are exposed to enhanced thermal compression.