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arXiv · 2610.22816

A Unified Solution to the Low-Mass X-ray Binary Diversity Puzzle: Saturated Magnetic Braking Coupled with Irradiation-Driven Winds

Zhu-Ling Deng·Xiang-Dong Li·Bo Wang·Philipp Podsiadlowski·Yong Shao·Dong-Dong Liu·Zhan-Wen Han
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Abstract

The standard magnetic braking (MB) model has long failed to explain key properties of low-mass X-ray binaries (LMXBs)---including their accretion rates, the formation of ultracompact binaries, and orbital expansion---casting doubt on binary evolution and gravitational-wave progenitor predictions. Phenomenological modifications exist, but a unified, physically grounded mechanism has been missing. Here we show that the overlooked coupling between magnetic saturation and irradiation-driven winds (IDW) provides this missing framework. Accretion-powered irradiation enhances the donor wind, which in turn amplifies MB exactly where needed. Our Saturated MB + IDW (SMB+IDW) model simultaneously resolves three outstanding discrepancies with no fine-tuning: (1) it reproduces the full observed distribution of accretion rates across persistent and transient LMXBs; (2) it naturally explains ultracompact X-ray binary formation; and (3) it quantitatively matches the orbital period distribution of descendant millisecond pulsar (MSP) binaries---a critical independent test failed by all previous models. Critically, the SMB+IDW model transforms MB from an externally imposed condition into a self-consistently regulated process tied to the accretion history. By unifying LMXB evolution to MSPs in a single physical picture, our work resolves the long-standing diversity puzzle and establishes a physics-based foundation for next-generation population synthesis, gravitational-wave progenitor predictions, and compact binary interpretation across cosmic time.

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Zhu-Ling Deng, Xiang-Dong Li, Bo Wang, Philipp Podsiadlowski, Yong Shao, Dong-Dong Liu, Zhan-Wen Han. 2026-10-16. A Unified Solution to the Low-Mass X-ray Binary Diversity Puzzle: Saturated Magnetic Braking Coupled with Irradiation-Driven Winds. https://arxiv.org/abs/2610.22816

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