From Wide Triples to UCXBs: Multimessenger Signatures of Dynamically-formed Black Hole-White Dwarf Systems in the LISA Band
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866917126682443776 |
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| author | Xuan, Zeyuan Shariat, Cheyanne Naoz, Smadar |
| author_facet | Xuan, Zeyuan Shariat, Cheyanne Naoz, Smadar |
| contents | Ultracompact X-ray binaries (UCXBs) are a subclass of low-mass X-ray binaries characterized by tight orbits and degenerate donors, which pose significant challenges to our understanding of their formation. Recent discoveries of black hole (BH) candidates with main-sequence (MS) or red giant (RG) companions suggest that BH-white dwarf (BH-WD) binaries are common in the Galactic field. Motivated by these observations and the fact that most massive stars are born in triples, we show that wide BH-WD systems can naturally form UCXBs through the eccentric Kozai-Lidov (EKL) mechanism. Notably, EKL-driven eccentricity excitations combined with gravitational wave (GW) emission and WD dynamical tides can effectively shrink and circularize the orbit, leading to mass-transferring BH-WD binaries. These systems represent promising multimessenger sources in both X-ray and GW observations. Specifically, we predict that the wide triple channel can produce $\sim3-27$ ($\sim1-5$) detectable UCXBs in the Milky Way (Andromeda galaxy), including $\sim1$ system observable by the mHz GW detection of LISA. If the final WD mass can reach sufficiently small values, this channel could contribute up to $\sim 10^3$ UCXBs in the Galaxy. Furthermore, the identification of tertiary companions in observed UCXBs would provide direct evidence for this formation pathway and yield unique insights into their dynamical origins. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_13264 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | From Wide Triples to UCXBs: Multimessenger Signatures of Dynamically-formed Black Hole-White Dwarf Systems in the LISA Band Xuan, Zeyuan Shariat, Cheyanne Naoz, Smadar High Energy Astrophysical Phenomena Astrophysics of Galaxies General Relativity and Quantum Cosmology Ultracompact X-ray binaries (UCXBs) are a subclass of low-mass X-ray binaries characterized by tight orbits and degenerate donors, which pose significant challenges to our understanding of their formation. Recent discoveries of black hole (BH) candidates with main-sequence (MS) or red giant (RG) companions suggest that BH-white dwarf (BH-WD) binaries are common in the Galactic field. Motivated by these observations and the fact that most massive stars are born in triples, we show that wide BH-WD systems can naturally form UCXBs through the eccentric Kozai-Lidov (EKL) mechanism. Notably, EKL-driven eccentricity excitations combined with gravitational wave (GW) emission and WD dynamical tides can effectively shrink and circularize the orbit, leading to mass-transferring BH-WD binaries. These systems represent promising multimessenger sources in both X-ray and GW observations. Specifically, we predict that the wide triple channel can produce $\sim3-27$ ($\sim1-5$) detectable UCXBs in the Milky Way (Andromeda galaxy), including $\sim1$ system observable by the mHz GW detection of LISA. If the final WD mass can reach sufficiently small values, this channel could contribute up to $\sim 10^3$ UCXBs in the Galaxy. Furthermore, the identification of tertiary companions in observed UCXBs would provide direct evidence for this formation pathway and yield unique insights into their dynamical origins. |
| title | From Wide Triples to UCXBs: Multimessenger Signatures of Dynamically-formed Black Hole-White Dwarf Systems in the LISA Band |
| topic | High Energy Astrophysical Phenomena Astrophysics of Galaxies General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2508.13264 |