Protostellar Outflows and Radiative Feedback from Massive Stars

TL;DR

This study uses radiation hydrodynamical simulations to explore how protostellar outflows and radiative feedback influence the formation and final mass of massive stars, revealing that outflows extend accretion duration and increase stellar mass.

Contribution

It introduces a detailed simulation of massive star formation including outflows and radiative feedback, highlighting their combined effect on prolonging accretion and increasing stellar mass.

Findings

Protostellar outflows create bipolar cavities facilitating anisotropic radiation escape.

Outflows extend the accretion phase, allowing stars to grow more massive.

Outflows lead to a higher final stellar mass compared to models without outflows.

Abstract

We carry out radiation hydrodynamical simulations of the formation of massive stars in the super-Eddington regime including both their radiative feedback and protostellar outflows. The calculations start from a prestellar core of dusty gas and continue until the star stops growing. The accretion ends when the remnants of the core are ejected, mostly by the force of the direct stellar radiation in the polar direction and elsewhere by the reradiated thermal infrared radiation. How long the accretion persists depends on whether the protostellar outflows are present. We set the mass outflow rate to 1% of the stellar sink particle's accretion rate. The outflows open a bipolar cavity extending to the core's outer edge, through which the thermal radiation readily escapes. The radiative flux is funneled into the polar directions while the core's collapse proceeds near the equator. The outflow thus extends the "flashlight effect", or anisotropic radiation field, found in previous studies from the few hundred AU scale of the circumstellar disk up to the 0.1 parsec scale of the core. The core's flashlight effect allows core gas to accrete on the disk for longer, in the same way that the disk's flashlight effect allows disk gas to accrete on the star for longer. Thus although the protostellar outflows remove material near the core's poles, causing slower stellar growth over the first few free-fall times, they also enable accretion to go on longer in our calculations. The outflows ultimately lead to stars of somewhat higher mass.