Protostellar Outflows and Radiative Feedback from Massive Stars. II. Feedback, Star Formation Efficiency, and Outflow Broadening

TL;DR

This study uses radiation-hydrodynamic simulations to explore how outflows and radiative feedback influence star formation efficiency and outflow structures in massive protostars, revealing the dominant role of radiative forces and outflow strength.

Contribution

It provides new insights into how outflow properties and radiative feedback regulate star formation efficiency and outflow morphology in massive star formation.

Findings

Star formation efficiency ranges from 20% to 50% depending on outflow strength.

Outflow momentum and cavity size significantly reduce radiative feedback effects.

Bipolar outflow opening angles increase from below 20° to 65° during protostellar evolution.

Abstract

We perform two-dimensional axially symmetric radiation-hydrodynamic simulations to assess the impact of outflows and radiative force feedback from massive protostars by varying when the protostellar outflow starts, the ratio of ejection to accretion rates, and the strength of the wide angle disk wind component. The star formation efficiency, i.e. the ratio of final stellar mass to initial core mass, is dominated by radiative forces and the ratio of outflow to accretion rates. Increasing this ratio has three effects: First, the protostar grows slower with a lower luminosity at any given time, lowering radiative feedback. Second, bipolar cavities cleared by the outflow are larger, further diminishing radiative feedback on disk and core scales. Third, the higher momentum outflow sweeps up more material from the collapsing envelope, decreasing the protostar's potential mass reservoir via entrainment. The star formation efficiency varies with the ratio of ejection to accretion rates from 50% in the case of very weak outflows to as low as 20% for very strong outflows. At latitudes between the low density bipolar cavity and the high density accretion disk, wide angle disk winds remove some of the gas, which otherwise would be part of the accretion flow onto the disk; varying the strength of these wide angle disk winds, however, alters the final star formation efficiency by only +/-6%. For all cases, the opening angle of the bipolar outflow cavity remains below 20 degree during early protostellar accretion phases, increasing rapidly up to 65 degree at the onset of radiation pressure feedback.