An Intermediate Mass Stripped Star in a 4.2-hour Orbit around a Compact Object
Abstract
From their discovery as radio pulsars to landmark multi-messenger observations of their mergers, double neutron stars have transformed our understanding of the extreme Universe and the formation of heavy elements (Drout et al. 2017; Abbott et al. 2017). Yet, uncertainties in their formation result in predicted merger rates spanning orders of magnitude (Tauris et al. 2017; Mandel & Broekgaarden 2022). The most critical stage occurs when a star is stripped of its hydrogen-rich envelope, causing the binary orbit to shrink drastically. Despite its fundamental role, the resulting tight binaries comprising a stripped star and neutron star have remained elusive. Here we report a ∼3.4 M⊙ stripped star (Ludwig et al. 2026; Drout et al. 2023; Götberg et al. 2023) orbiting an unseen companion every 4.2 hours. Our orbital and spectroscopic analysis excludes a normal star, which would not fit within the orbit, as well as a second stripped star which would have been detectable in our spectra. Adding constraints from high cadence photometry gives a 99.4% probability that the companion is too massive to be a white dwarf, making a neutron star the most likely companion. We model the system's future and predict that the stripped star will transfer mass again before exploding as a hydrogen-free supernova, leaving a bound pair of neutron stars that will merge after 220 Myr. This system reveals a previously unconstrained phase of binary evolution, uncovering a new class of systems that probes the uncertain physics of massive stars, linking to observable gravitational-wave sources.
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BibTeX
@misc{ludwig2026intermediate,
title = {{An Intermediate Mass Stripped Star in a 4.2-hour Orbit around a Compact Object}},
author = {Bethany Ludwig and Maria R. Drout and Ylva Götberg and Alexander Laroche and Katie Auchettl and Alejandro Vigna-Gómez and Katelyn Breivik and Cole Johnston and Eva Laplace and Vikram S. Dhillon and Hugues Sana},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.35539},
eprint = {2610.35539},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.35539},
}
RIS
TY - UNPB
TI - An Intermediate Mass Stripped Star in a 4.2-hour Orbit around a Compact Object
AU - Bethany Ludwig
AU - Maria R. Drout
AU - Ylva Götberg
AU - Alexander Laroche
AU - Katie Auchettl
AU - Alejandro Vigna-Gómez
AU - Katelyn Breivik
AU - Cole Johnston
AU - Eva Laplace
AU - Vikram S. Dhillon
AU - Hugues Sana
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2610.35539
UR - https://arxiv.org/abs/2610.35539
AB - From their discovery as radio pulsars to landmark multi-messenger observations of their mergers, double neutron stars have transformed our understanding of the extreme Universe and the formation of heavy elements (Drout et al. 2017; Abbott et al. 2017). Yet, uncertainties in their formation result in predicted merger rates spanning orders of magnitude (Tauris et al. 2017; Mandel & Broekgaarden 2022). The most critical stage occurs when a star is stripped of its hydrogen-rich envelope, causing the binary orbit to shrink drastically. Despite its fundamental role, the resulting tight binaries comprising a stripped star and neutron star have remained elusive. Here we report a ∼3.4 M_⊙ stripped star (Ludwig et al. 2026; Drout et al. 2023; Götberg et al. 2023) orbiting an unseen companion every 4.2 hours. Our orbital and spectroscopic analysis excludes a normal star, which would not fit within the orbit, as well as a second stripped star which would have been detectable in our spectra. Adding constraints from high cadence photometry gives a 99.4% probability that the companion is too massive to be a white dwarf, making a neutron star the most likely companion. We model the system's future and predict that the stripped star will transfer mass again before exploding as a hydrogen-free supernova, leaving a bound pair of neutron stars that will merge after 220 Myr. This system reveals a previously unconstrained phase of binary evolution, uncovering a new class of systems that probes the uncertain physics of massive stars, linking to observable gravitational-wave sources.
ER -