Journal Article

A wide star–black-hole binary system from radial-velocity measurements

Lu, Youjun, Di Stefano, Rosanne, Gu, Wei-Min, Liu, Jifeng, Shao, Lijing, Wang, Yilun, Lattanzi, Mario, Li, Xiangdong, Zhang, Tianmeng, Howard, Andrew W., Lei, Yajuan, Zhang, Junbo, Niu, Zexi, Belczynski, Krzysztof, Zhao, Gang, Zhang, Lan, Zheng, Zheng, Bai, Zhongrui, Bai, Yu, Ren, Juanjuan, Corradi, Romano, Wu, Jianfeng, Wang, Huijuan, Wang, Tinggui, Yuan, Hailong, Liao, Shilong, Han, Zhanwen, Rebolo, Rafael, Wang, Xiaofeng, Bregman, Joel, Shao, Yong, Wang, Wei, Gao, Qing, Dong, Yiqiao, Wang, Song, Shen, Rongfeng, Soria, Roberto, Zhao, Yongheng, Chu, Yaoquan, Mu, Xiaoyong, Cui, Xiangqun, Cui, Kaiming, Zhang, Jujia, Isaacson, Howard, Liu, Qingzhong, Zhang, Wei, Justham, Stephen, Wang, Junfeng, Wang, Xiaoli, Qi, Zhaoxiang, Zheng, Chuanjie, Cabrera-Lavers, Antonio, Casares, Jorge, Heger, Alexander, Zhang, Haotong

2019

Overview

All stellar-mass black holes have hitherto been identified by X-rays emitted from gas that is accreting onto the black hole from a companion star. These systems are all binaries with a black-hole mass that is less than 30 times that of the Sun 1 – 4 . Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star–black-hole binaries 5 , 6 . When the black hole is not accreting gas, it can be found through radial-velocity measurements of the motion of the companion star. Here we report radial-velocity measurements taken over two years of the Galactic B-type star, LB-1. We find that the motion of the B star and an accompanying Hα emission line require the presence of a dark companion with a mass of 68 − 13 + 11 solar masses, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system. Gravitational-wave experiments have detected black holes of similar mass, but the formation of such massive ones in a high-metallicity environment would be extremely challenging within current stellar evolution theories. Radial-velocity measurements of a Galactic B-type star show a dark companion that seems to be a black hole of about 68 solar masses, in a widely spaced binary system.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/33/34/4118 / 639/33/34/4126 / Astronomical spectroscopy / B stars / Binary stars / Binary system / Black holes / Black holes (Astronomy) / Companion stars / Deposition / Emission lines / Extinction / Gravitational waves / Gravity / H alpha line / Humanities and Social Sciences / Light / Measurement / Metallicity / Methods / multidisciplinary / Observations / Orbits / Science / Science (multidisciplinary) / Space telescopes / Speed / Stars / Stars, Double / Stellar evolution / Velocity / X-rays