A Be star-black hole binary with a wide orbit from LAMOST time-domain survey
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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866910973350117376 |
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| author | An, Qian-Yu Huang, Yang Gu, Wei-Min Shao, Yong Zhang, Zhi-Xiang Yi, Tuan Lailey, B. D. Sigut, T. A. A. Rocha, Kyle Akira Sun, Meng Gossage, Seth Gao, Shi-Jie Weng, Shan-Shan Wang, Song Zhang, Bowen Zhao, Xinlin Qi, Senyu Liao, Shilong Ji, Jianghui Wang, Junfeng Wu, Jianfeng Sun, Mouyuan Li, Xiang-Dong Liu, Jifeng |
| author_facet | An, Qian-Yu Huang, Yang Gu, Wei-Min Shao, Yong Zhang, Zhi-Xiang Yi, Tuan Lailey, B. D. Sigut, T. A. A. Rocha, Kyle Akira Sun, Meng Gossage, Seth Gao, Shi-Jie Weng, Shan-Shan Wang, Song Zhang, Bowen Zhao, Xinlin Qi, Senyu Liao, Shilong Ji, Jianghui Wang, Junfeng Wu, Jianfeng Sun, Mouyuan Li, Xiang-Dong Liu, Jifeng |
| contents | Binary systems consisting of an early type star and a black hole (BH) are crucial for understanding various astrophysical phenomena, particularly the origins of detected gravitational wave sources. Be binary systems are expected to represent a key evolutionary stage in hosting BHs. However, while hundreds of Be X-ray binaries are known, the only confirmed BH candidate in a Be binary remains highly controversial. We report the discovery of ALS 8814, a Be star-BH binary with a moderately eccentric ($e = 0.23$) and wide orbit ($P = 176.6$ days), revealed by the radial velocity (RV) measurement of the visible Be star. Our analysis, combining flux-calibrated spectra in the Balmer discontinuity region and spectral template matching, yields a mass of $11.2^{+1.4}_{-1.2}$ $M_\odot$ for the Be star. The minimum mass of the unseen companion, assuming an edge-on inclination ($i = 90^{\circ}$), is $9.8\pm 0.7\,M_\odot$. We rule out the presence of non-degenerate companions in ALS 8814, indicating that it can only be a BH. This discovery represents a robust case of a Be-BH binary, identified purely through precise RV measurements from a single set of lines. The extremely low peculiar velocity of ALS 8814 suggests that the BH is formed via a direct core-collapse with a negligible natal kick, implying an almost perfect alignment between the Be star's spin and the orbital plane. In this context, the binary's inclination angle is estimated to be 22$^{\circ}$-49$^{\circ}$ by analyzing the shallow double-peaked profile of the H$α$ emission line. This inclination range corresponds to a BH mass estimate between $15\,M_\odot$ and $58\,M_\odot$. As the only unambiguous Be-BH binary system known to date, ALS 8814 provides valuable constraints on the BH formation in a binary system with a high-mass companion. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2505_23151 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | A Be star-black hole binary with a wide orbit from LAMOST time-domain survey An, Qian-Yu Huang, Yang Gu, Wei-Min Shao, Yong Zhang, Zhi-Xiang Yi, Tuan Lailey, B. D. Sigut, T. A. A. Rocha, Kyle Akira Sun, Meng Gossage, Seth Gao, Shi-Jie Weng, Shan-Shan Wang, Song Zhang, Bowen Zhao, Xinlin Qi, Senyu Liao, Shilong Ji, Jianghui Wang, Junfeng Wu, Jianfeng Sun, Mouyuan Li, Xiang-Dong Liu, Jifeng Solar and Stellar Astrophysics High Energy Astrophysical Phenomena Binary systems consisting of an early type star and a black hole (BH) are crucial for understanding various astrophysical phenomena, particularly the origins of detected gravitational wave sources. Be binary systems are expected to represent a key evolutionary stage in hosting BHs. However, while hundreds of Be X-ray binaries are known, the only confirmed BH candidate in a Be binary remains highly controversial. We report the discovery of ALS 8814, a Be star-BH binary with a moderately eccentric ($e = 0.23$) and wide orbit ($P = 176.6$ days), revealed by the radial velocity (RV) measurement of the visible Be star. Our analysis, combining flux-calibrated spectra in the Balmer discontinuity region and spectral template matching, yields a mass of $11.2^{+1.4}_{-1.2}$ $M_\odot$ for the Be star. The minimum mass of the unseen companion, assuming an edge-on inclination ($i = 90^{\circ}$), is $9.8\pm 0.7\,M_\odot$. We rule out the presence of non-degenerate companions in ALS 8814, indicating that it can only be a BH. This discovery represents a robust case of a Be-BH binary, identified purely through precise RV measurements from a single set of lines. The extremely low peculiar velocity of ALS 8814 suggests that the BH is formed via a direct core-collapse with a negligible natal kick, implying an almost perfect alignment between the Be star's spin and the orbital plane. In this context, the binary's inclination angle is estimated to be 22$^{\circ}$-49$^{\circ}$ by analyzing the shallow double-peaked profile of the H$α$ emission line. This inclination range corresponds to a BH mass estimate between $15\,M_\odot$ and $58\,M_\odot$. As the only unambiguous Be-BH binary system known to date, ALS 8814 provides valuable constraints on the BH formation in a binary system with a high-mass companion. |
| title | A Be star-black hole binary with a wide orbit from LAMOST time-domain survey |
| topic | Solar and Stellar Astrophysics High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2505.23151 |