Radiative Feedback in Population III Protostellar Growth: HI Shielding \& HII Region Trapping

Avi Chen; Shyam H. Menon; Blakesley Burkhart; Piyush Sharda; Claire E. Williams; Smadar Naoz; Naoki Yoshida; Federico Marinacci; Mark Vogelsberger; William Lake

arXiv · 2604.00197

Radiative Feedback in Population III Protostellar Growth: HI Shielding \& HII Region Trapping

Avi Chen·Shyam H. Menon·Blakesley Burkhart·Piyush Sharda·Claire E. Williams·Smadar Naoz·Naoki Yoshida·Federico Marinacci·Mark Vogelsberger·William Lake

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Abstract

We present a suite of radiation-magnetohydrodynamics simulations from the Popsicle project that follow the long-term growth ($\sim 50$ kyr) of primordial protostars while self-consistently coupling radiation, turbulence, and magnetic fields. The simulation suite is designed to quantify the relative impacts of the pathways of radiative feedback in Pop III stars -- the extreme-ultraviolet (EUV) ionization and Lyman-Werner (LW) dissociation -- by considering simulations with/without their inclusion. We find that without HI shielding, LW feedback can suppress and ultimately terminate accretion. With HI shielding, the large column densities near the protostar significantly weaken LW feedback. In the polar direction, atomic hydrogen fully shields LW radiation where H$_2$ self-shielding alone is insufficient. This leads to lower gas temperatures near the protostar and higher accretion rates, yielding larger final stellar masses than in models without shielding. The HII region remain confined, extending $\sim$100 AU beyond the sink accretion radius (75 AU), as dense gravitationally bound gas sustains high recombination rates and prevents sustained pressure-driven breakout. Turbulence and magnetic fields may also contribute to its confinement, even at high ionizing luminosities. These results demonstrate that the interplay of gas dynamics, shielding, and radiative feedback can significantly alter the growth of Pop III stars. We discuss the implications for the initial mass function of primordial stars and the influence of feedback from early stellar populations.

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Avi Chen, Shyam H. Menon, Blakesley Burkhart, Piyush Sharda, Claire E. Williams, Smadar Naoz, Naoki Yoshida, Federico Marinacci, Mark Vogelsberger, William Lake. 2026-03-31. Radiative Feedback in Population III Protostellar Growth: HI Shielding \& HII Region Trapping. https://arxiv.org/abs/2604.00197

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