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

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Main Authors: Yang, Xing-Peng, Xu, Kun, Gao, Zhi-Fu, Jiang, Long, Chen, Wen-Cong
Format: Preprint
Published: 2025
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author Yang, Xing-Peng
Xu, Kun
Gao, Zhi-Fu
Jiang, Long
Chen, Wen-Cong
author_facet Yang, Xing-Peng
Xu, Kun
Gao, Zhi-Fu
Jiang, Long
Chen, Wen-Cong
contents 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 $L_{\rm X}=1.09^{+0.02}_{-0.01}\times10^{38}~ \rm erg\,s^{-1}$ 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 like 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 $7.7~ \rm minutes$, 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 $10^{38}~\rm erg\,s^{-1}$. 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.
format Preprint
id arxiv_https___arxiv_org_abs_2505_12689
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Formation of a Possible Black-hole Ultracompact X-ray Binary with the Shortest Orbital Period
Yang, Xing-Peng
Xu, Kun
Gao, Zhi-Fu
Jiang, Long
Chen, Wen-Cong
High Energy Astrophysical Phenomena
Solar and Stellar Astrophysics
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 $L_{\rm X}=1.09^{+0.02}_{-0.01}\times10^{38}~ \rm erg\,s^{-1}$ 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 like 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 $7.7~ \rm minutes$, 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 $10^{38}~\rm erg\,s^{-1}$. 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.
title Formation of a Possible Black-hole Ultracompact X-ray Binary with the Shortest Orbital Period
topic High Energy Astrophysical Phenomena
Solar and Stellar Astrophysics
url https://arxiv.org/abs/2505.12689