From the Milky Way to the Early Universe: How Metallicity Shapes the Formation of Double Neutron Stars
Abstract
Among the compact binaries detected through gravitational wave (GW) emission, double neutron stars (DNSs) hold the unique distinction of having well-characterized local analogs in the Milky Way. However, understanding their broader cosmological population remains challenging due to the complex metallicity-dependent evolution of their progenitors. Using the detailed binary population synthesis code POSYDON, we model DNS formation across a cosmological range of metallicities. We find that while DNSs are predominantly formed through common envelope evolution, metallicity-dependent radial expansion and stellar wind mass loss bifurcates the pathway into distinct subchannels, producing systematically distinct merging populations at different metallicities. Notably, our best representative Galactic models predict local merger rates in broad agreement with the latest GWTC-5 constraints, suggesting that the populations observed via radio pulsar surveys and through GW emission need not be in tension. Contrary to previous studies, we demonstrate that the intrinsic merger efficiency increases toward low metallicities, a trend robust across varying binary evolution assumptions, although the magnitude and the underlying stellar processes driving this enhancement vary across metallicity regimes. When convolved with the cosmic star formation history, our models reveal that the majority of merging DNSs originate from progenitors in the range ∼ 0.1 Z⊙ − Z⊙, with significant supersolar contributions. Furthermore, we show that weaker stellar winds at low metallicities produce DNS mergers with systematically more symmetric mass ratios (q ≳0.9). Additionally, we assess detectability within proposed configurations for third-generation GW observatories. Our study provides a framework for interpreting the cosmological DNS population in the upcoming multi-messenger era.
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BibTeX
@misc{chattaraj2026from,
title = {{From the Milky Way to the Early Universe: How Metallicity Shapes the Formation of Double Neutron Stars}},
author = {Abhishek Chattaraj and Jeff J. Andrews and Monica Gallegos-Garcia and Max M. Briel and Michael Zevin and Tassos Fragos and Emmanouil Zapartas and David R. Aguilera-Dena and Seth Gossage and Anarya Ray and Philipp M. Srivastava and Zepei Xing},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.05773},
eprint = {2610.05773},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.05773},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - From the Milky Way to the Early Universe: How Metallicity Shapes the Formation of Double Neutron Stars
AU - Abhishek Chattaraj
AU - Jeff J. Andrews
AU - Monica Gallegos-Garcia
AU - Max M. Briel
AU - Michael Zevin
AU - Tassos Fragos
AU - Emmanouil Zapartas
AU - David R. Aguilera-Dena
AU - Seth Gossage
AU - Anarya Ray
AU - Philipp M. Srivastava
AU - Zepei Xing
PY - 2026
DA - 2026/10/06
PB - arXiv
DO - 10.48550/arxiv.2610.05773
UR - https://arxiv.org/abs/2610.05773
AB - Among the compact binaries detected through gravitational wave (GW) emission, double neutron stars (DNSs) hold the unique distinction of having well-characterized local analogs in the Milky Way. However, understanding their broader cosmological population remains challenging due to the complex metallicity-dependent evolution of their progenitors. Using the detailed binary population synthesis code POSYDON, we model DNS formation across a cosmological range of metallicities. We find that while DNSs are predominantly formed through common envelope evolution, metallicity-dependent radial expansion and stellar wind mass loss bifurcates the pathway into distinct subchannels, producing systematically distinct merging populations at different metallicities. Notably, our best representative Galactic models predict local merger rates in broad agreement with the latest GWTC-5 constraints, suggesting that the populations observed via radio pulsar surveys and through GW emission need not be in tension. Contrary to previous studies, we demonstrate that the intrinsic merger efficiency increases toward low metallicities, a trend robust across varying binary evolution assumptions, although the magnitude and the underlying stellar processes driving this enhancement vary across metallicity regimes. When convolved with the cosmic star formation history, our models reveal that the majority of merging DNSs originate from progenitors in the range ∼ 0.1 Z_⊙ − Z_⊙, with significant supersolar contributions. Furthermore, we show that weaker stellar winds at low metallicities produce DNS mergers with systematically more symmetric mass ratios (q ≳0.9). Additionally, we assess detectability within proposed configurations for third-generation GW observatories. Our study provides a framework for interpreting the cosmological DNS population in the upcoming multi-messenger era.
ER -