First hydrodynamics simulations of radiation forces and photoionization feedback in massive star formation

TL;DR

This study presents the first hydrodynamics simulations of massive star formation that incorporate radiation forces, photoionization, and protostellar outflows, revealing radiation feedback as the key regulator of the final stellar mass.

Contribution

It introduces the first comprehensive simulations including radiation forces and photoionization feedback in massive star formation models, highlighting their roles in limiting stellar growth.

Findings

Protostellar outflows alone limit stellar mass only with finite reservoirs.

Photoionization broadens outflow cavities but does not limit accretion.

Radiation forces ultimately shut down accretion, setting the final stellar mass.

Abstract

We present the first simulations of the formation and feedback of massive stars which account for radiation forces as well as photoionization feedback (along with protostellar outflows). In two different accretion scenarios modeled, we determine the relative strength of these feedback components and derive the size of the reservoir from which the forming stars gained their masses. We find that protostellar outflows alone limit the stellar mass growth only in an accretion scenario with a finite mass reservoir; when including accretion and ram pressure from large scales (> 0.1 pc), protostellar outflows do not limit stellar mass growth at all. Photoionization and HII regions dominate the feedback ladder only at later times and only on large scales. Specifically, photoionization yields a broadening of the bipolar outflow cavities and a reduction of the gravitational infall momentum by about 50 percent, but does not limit the stellar mass accretion. On the other hand, we find radiation forces restrain the gravitational infall toward the circumstellar disk, impact the gravito-centrifugal equilibrium at the outer edge of the disk, and eventually shut down stellar accretion completely. The most massive star formed in the simulations accreted 95 solar masses before disk destruction; this mass was drawn-in from an accretion reservoir of approximately 240 solar masses and 0.24 pc in radius. In the regime of very massive stars, the final mass of these stars is controlled by their own radiation force feedback.