BE Lyncis: A Pulsating Star in the Most Eccentric Binary with a Massive Unseen Companion
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| Format: | Preprint |
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2026
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| _version_ | 1866915941462310912 |
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| author | Niu, Jia-Shu Zhang, Ying Xue, Hui-Fang |
| author_facet | Niu, Jia-Shu Zhang, Ying Xue, Hui-Fang |
| contents | We report the discovery of an exceptionally eccentric binary system, BE Lyncis (BE~Lyn), which might host a compact companion with mass $\gtrsim 2.5~M_{\odot}$. By combining TESS photometry with an extensive set of times of maximum light spanning 39~years, we identify BE~Lyn as a high-amplitude $δ$ Scuti star in a binary with an orbital period of $\approx15.9$~years and an extraordinary eccentricity of $e=0.9989^{+0.0008}_{-0.0021}$ ($>0.9968$ at 95% confidence) -- the most extreme eccentricity reliably measured for any binary system. Dynamical constraints limit the orbital inclination to $i \lesssim 10.1^{\circ}$, implying a companion mass $M_2 \gtrsim 2.5~M_{\odot}$, which identifies the companion as a compact object. This mass points to it most likely being a black hole; if instead it is a rapidly rotating neutron star, it would be the most massive known. If the black hole interpretation holds, it would be the closest such object to Earth. This system provides a unique laboratory for studying asteroseismology in strong gravitational fields, as well as the formation and evolution of extremely eccentric binaries. Our work demonstrates the use of the light-travel time effect in a pulsating star to reveal a compact companion, offering a novel method for detecting black holes in non-interacting binaries. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2601_12999 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | BE Lyncis: A Pulsating Star in the Most Eccentric Binary with a Massive Unseen Companion Niu, Jia-Shu Zhang, Ying Xue, Hui-Fang Solar and Stellar Astrophysics High Energy Astrophysical Phenomena We report the discovery of an exceptionally eccentric binary system, BE Lyncis (BE~Lyn), which might host a compact companion with mass $\gtrsim 2.5~M_{\odot}$. By combining TESS photometry with an extensive set of times of maximum light spanning 39~years, we identify BE~Lyn as a high-amplitude $δ$ Scuti star in a binary with an orbital period of $\approx15.9$~years and an extraordinary eccentricity of $e=0.9989^{+0.0008}_{-0.0021}$ ($>0.9968$ at 95% confidence) -- the most extreme eccentricity reliably measured for any binary system. Dynamical constraints limit the orbital inclination to $i \lesssim 10.1^{\circ}$, implying a companion mass $M_2 \gtrsim 2.5~M_{\odot}$, which identifies the companion as a compact object. This mass points to it most likely being a black hole; if instead it is a rapidly rotating neutron star, it would be the most massive known. If the black hole interpretation holds, it would be the closest such object to Earth. This system provides a unique laboratory for studying asteroseismology in strong gravitational fields, as well as the formation and evolution of extremely eccentric binaries. Our work demonstrates the use of the light-travel time effect in a pulsating star to reveal a compact companion, offering a novel method for detecting black holes in non-interacting binaries. |
| title | BE Lyncis: A Pulsating Star in the Most Eccentric Binary with a Massive Unseen Companion |
| topic | Solar and Stellar Astrophysics High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2601.12999 |