FORGE'd in Fragments: Pop III star formation in a Milky Way-like progenitor halo
Abstract
We present a radiation-magnetohydrodynamic (RMHD) cosmological zoom-in simulation of Pop III star formation, drawing initial conditions from a Milky Way-like progenitor halo at redshift z ∼ 21. We follow the collapse of primordial gas over 10 orders of magnitude, through to the formation of an accretion disk that becomes gravitationally unstable Δt ∼ −3 kyr before the first protostar's formation. Prominent spiral arms then develop and fragment vigorously, producing ∼ 60 sink formation events over the first $8$ kyr post-collapse evolution, with a total stellar mass reaching > 150 M⊙ by $15$ kyr, the end of our simulation. The disk remains magnetically supercritical throughout: the mass-to-flux ratio falls from μΦ∼ 102-103 to ∼ 15 by $15$ kyr, as the inflow brings in magnetic flux. The magnetic energy in the disk remains sub-dominant throughout, but grows by ∼ 3.5 orders of magnitude after the first star forms. The disk starts sub-virial and reaches virial equilibrium within ∼ 2 kyr. The total stellar mass of the population grows as M* ∝ t2, confirming the prediction of accelerating accretion in self-gravitating turbulent collapse, at rates of Ṁ ∼ 10−3-10−2 M⊙ yr−1. The star formation efficiency reaches ≈ 90% within the disk (after ≈ 11 kyr; ≈ 80% at $9.5$ kyr) and ∼ 50% within a $0.1$ pc sphere. We find a top heavy IMF (dN/dm ∝ m−α) with a high-mass slope α≈ 1. The cosmological environment sets the boundary conditions of the disk: an envelope delivers ∼ 3× 10−3 M⊙ yr−1 to the outer edge of a disk with a radius of ∼ 103 AU; the disk spreads and, in our simulation, its fragmentation sites move outward, from ∼ 500 to ∼ 1350\,AU, until it has been depleted.
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BibTeX
@misc{pustovoit2026forged,
title = {{FORGE'd in Fragments: Pop III star formation in a Milky Way-like progenitor halo}},
author = {Vasilii Pustovoit and Shivan Khullar and Norman Murray and Yasmine J. Meziani and Claude-André Faucher-Giguère and Philip F. Hopkins and Michael Y. Grudić and J. Richard Bond},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.08603},
eprint = {2611.08603},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.08603},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - FORGE'd in Fragments: Pop III star formation in a Milky Way-like progenitor halo
AU - Vasilii Pustovoit
AU - Shivan Khullar
AU - Norman Murray
AU - Yasmine J. Meziani
AU - Claude-André Faucher-Giguère
AU - Philip F. Hopkins
AU - Michael Y. Grudić
AU - J. Richard Bond
PY - 2026
DA - 2026/11/05
PB - arXiv
DO - 10.48550/arxiv.2611.08603
UR - https://arxiv.org/abs/2611.08603
AB - We present a radiation-magnetohydrodynamic (RMHD) cosmological zoom-in simulation of Pop III star formation, drawing initial conditions from a Milky Way-like progenitor halo at redshift z ∼ 21. We follow the collapse of primordial gas over 10 orders of magnitude, through to the formation of an accretion disk that becomes gravitationally unstable Δt ∼ −3 kyr before the first protostar's formation. Prominent spiral arms then develop and fragment vigorously, producing ∼ 60 sink formation events over the first $8$ kyr post-collapse evolution, with a total stellar mass reaching > 150 M_⊙ by $15$ kyr, the end of our simulation. The disk remains magnetically supercritical throughout: the mass-to-flux ratio falls from μ_Φ∼ 10^2-10^3 to ∼ 15 by $15$ kyr, as the inflow brings in magnetic flux. The magnetic energy in the disk remains sub-dominant throughout, but grows by ∼ 3.5 orders of magnitude after the first star forms. The disk starts sub-virial and reaches virial equilibrium within ∼ 2 kyr. The total stellar mass of the population grows as M_* ∝ t^2, confirming the prediction of accelerating accretion in self-gravitating turbulent collapse, at rates of Ṁ ∼ 10^−3-10^−2 M_⊙ yr^−1. The star formation efficiency reaches ≈ 90% within the disk (after ≈ 11 kyr; ≈ 80% at $9.5$ kyr) and ∼ 50% within a $0.1$ pc sphere. We find a top heavy IMF (dN/dm ∝ m^−α) with a high-mass slope α≈ 1. The cosmological environment sets the boundary conditions of the disk: an envelope delivers ∼ 3× 10^−3 M_⊙ yr^−1 to the outer edge of a disk with a radius of ∼ 10^3 AU; the disk spreads and, in our simulation, its fragmentation sites move outward, from ∼ 500 to ∼ 1350\,AU, until it has been depleted.
ER -