Formation of a Possible Black-hole Ultracompact X-Ray Binary with the Shortest Orbital Period

In the bulge of M31, the Chandra observations discovered a possible black hole (BH) ultracompact X-ray binary (UCXB) Seq.1 with an orbital period of 7.7 minutes and a maximum X-ray luminosity ${L}_{{\rm{X}}}=1.0{9}_{-0.01}^{+0.02}\,\times 1{0}^{38}\,{\rm{erg}}\,{{\rm{s}}}^{-1}$ in the 0.5–8 keV band...

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Main Authors: Xing-Peng Yang, Kun Xu, Zhi-Fu Gao, Long Jiang, Wen-Cong Chen
Format: Article
Language:English
Published: IOP Publishing 2025-01-01
Series:The Astrophysical Journal
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Online Access:https://doi.org/10.3847/1538-4357/add479
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author Xing-Peng Yang
Kun Xu
Zhi-Fu Gao
Long Jiang
Wen-Cong Chen
author_facet Xing-Peng Yang
Kun Xu
Zhi-Fu Gao
Long Jiang
Wen-Cong Chen
author_sort Xing-Peng Yang
collection DOAJ
description In the bulge of M31, the Chandra observations discovered a possible black hole (BH) ultracompact X-ray binary (UCXB) Seq.1 with an orbital period of 7.7 minutes and a maximum X-ray luminosity ${L}_{{\rm{X}}}=1.0{9}_{-0.01}^{+0.02}\,\times 1{0}^{38}\,{\rm{erg}}\,{{\rm{s}}}^{-1}$ in the 0.5–8 keV band. The minimum orbital period of the BH UCXBs predicted by the standard magnetic braking (MB) model is longer than 8.3 minutes. In this work, we investigate whether the convection- and rotation-boosted (CARB) MB prescription can account for the formation of a BH UCXB such as Seq.1. Our detailed stellar evolution models indicate that the CARB MB law can drive isolated BH–main-sequence (MS) binaries to evolve toward BH UCXBs with an orbital period of 7.7 minutes, in which a low-mass white dwarf transfers the material onto a BH in a short-term mass-transfer episode, producing an X-ray luminosity of ∼10 ^38 erg s ^−1 . We also obtain an initial parameter space of BH–MS binaries as the progenitors of Seq.1 in the donor-star masses and orbital periods plane, which can be applied to future population synthesis simulations. If Seq.1 is indeed a BH UCXB, future spaceborne gravitational wave (GW) detectors can detect the low-frequency GW signals from this source, and a tidal disruption event will be expected after 0.12 Myr.
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spelling doaj-art-bd623794d5fe400382853dd2bf0906182025-08-20T03:30:43ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01986221910.3847/1538-4357/add479Formation of a Possible Black-hole Ultracompact X-Ray Binary with the Shortest Orbital PeriodXing-Peng Yang0https://orcid.org/0009-0001-6764-106XKun Xu1https://orcid.org/0000-0002-9739-8929Zhi-Fu Gao2https://orcid.org/0000-0002-0138-3360Long Jiang3https://orcid.org/0000-0002-2479-1295Wen-Cong Chen4https://orcid.org/0000-0002-0785-5349School of Science, Qingdao University of Technology , Qingdao 266525, People’s Republic of China ; chenwc@pku.edu.cnSchool of Science, Qingdao University of Technology , Qingdao 266525, People’s Republic of China ; chenwc@pku.edu.cnXinjiang Astronomical Observatory, Chinese Academy of Sciences , Urumqi, Xinjiang 830011, People’s Republic of ChinaSchool of Science, Qingdao University of Technology , Qingdao 266525, People’s Republic of China ; chenwc@pku.edu.cn; School of Physics and Electrical Information, Shangqiu Normal University , Shangqiu 476000, People’s Republic of ChinaSchool of Science, Qingdao University of Technology , Qingdao 266525, People’s Republic of China ; chenwc@pku.edu.cn; School of Physics and Electrical Information, Shangqiu Normal University , Shangqiu 476000, People’s Republic of ChinaIn the bulge of M31, the Chandra observations discovered a possible black hole (BH) ultracompact X-ray binary (UCXB) Seq.1 with an orbital period of 7.7 minutes and a maximum X-ray luminosity ${L}_{{\rm{X}}}=1.0{9}_{-0.01}^{+0.02}\,\times 1{0}^{38}\,{\rm{erg}}\,{{\rm{s}}}^{-1}$ in the 0.5–8 keV band. The minimum orbital period of the BH UCXBs predicted by the standard magnetic braking (MB) model is longer than 8.3 minutes. In this work, we investigate whether the convection- and rotation-boosted (CARB) MB prescription can account for the formation of a BH UCXB such as Seq.1. Our detailed stellar evolution models indicate that the CARB MB law can drive isolated BH–main-sequence (MS) binaries to evolve toward BH UCXBs with an orbital period of 7.7 minutes, in which a low-mass white dwarf transfers the material onto a BH in a short-term mass-transfer episode, producing an X-ray luminosity of ∼10 ^38 erg s ^−1 . We also obtain an initial parameter space of BH–MS binaries as the progenitors of Seq.1 in the donor-star masses and orbital periods plane, which can be applied to future population synthesis simulations. If Seq.1 is indeed a BH UCXB, future spaceborne gravitational wave (GW) detectors can detect the low-frequency GW signals from this source, and a tidal disruption event will be expected after 0.12 Myr.https://doi.org/10.3847/1538-4357/add479X-ray binary starsStellar evolutionBlack holesWhite dwarf starsGravitational wave sources
spellingShingle Xing-Peng Yang
Kun Xu
Zhi-Fu Gao
Long Jiang
Wen-Cong Chen
Formation of a Possible Black-hole Ultracompact X-Ray Binary with the Shortest Orbital Period
The Astrophysical Journal
X-ray binary stars
Stellar evolution
Black holes
White dwarf stars
Gravitational wave sources
title Formation of a Possible Black-hole Ultracompact X-Ray Binary with the Shortest Orbital Period
title_full Formation of a Possible Black-hole Ultracompact X-Ray Binary with the Shortest Orbital Period
title_fullStr Formation of a Possible Black-hole Ultracompact X-Ray Binary with the Shortest Orbital Period
title_full_unstemmed Formation of a Possible Black-hole Ultracompact X-Ray Binary with the Shortest Orbital Period
title_short Formation of a Possible Black-hole Ultracompact X-Ray Binary with the Shortest Orbital Period
title_sort formation of a possible black hole ultracompact x ray binary with the shortest orbital period
topic X-ray binary stars
Stellar evolution
Black holes
White dwarf stars
Gravitational wave sources
url https://doi.org/10.3847/1538-4357/add479
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