FORGE'd in the Early Universe: The Effect of Protostellar Outflows on Pop III Accretion

TL;DR

This study uses advanced RMHD simulations to explore how protostellar jets influence the growth and environment of the first generation of stars, revealing their critical role in regulating star mass and feedback in the early universe.

Contribution

It presents the first detailed simulation showing how protostellar jets regulate Pop III star formation and their surroundings, highlighting the importance of magnetic fields and disk dynamics.

Findings

Protostellar jets regulate accretion and final star mass.

Jets drive outflows that slow infall of gas.

The circumstellar disk remains gravitationally stable.

Abstract

We present a cosmological zoom-in radiation magneto-hydrodynamic (RMHD) simulation, using FORGE'd in FIRE, that follows the formation, growth, and evolution of a single metal-free Pop. III (proto)star at redshift $z \sim 14$. The simulation captures a rotationally supported circumstellar disk and protostellar jets, both resolved down to $<100$ au scales. We find the star grows to $\sim 27$ M$_{\odot}$ over $31,000$ years, with its final mass regulated by accretion and protostellar jets. Protostellar jets form because the magnetic mass-to-flux ratio lies within the regime that allows jet launching, and they are further enabled by a rotating circumstellar disk with sufficient gas-magnetic-field coupling, both present in this simulation. These jets regulate accretion onto the (proto)star and drive outflows that collide with infalling gas, slowing inflow at large radii due to the substantial momentum they carry. A circumstellar disk forms, extending out to $\sim 0.01$ pc, which remains gravitationally stable (Q $\gg 1$). The stability of the disk is maintained through both thermal support and turbulence. In this paper we focus on how jets play a critical role not only in shaping the final masses of Pop. III stars but also in directly influencing their surroundings by regulating accretion. These results will provide important insights into the initial mass function and feedback processes in the earliest star-forming regions of the Universe.