A wide star-black-hole binary system from radial-velocity measurements
Soria, Roberto; Zhao, Gang; Wang, Wei; Wang, Xiaoli; Niu, Zexi; Liu, Jifeng; Han, Zhanwen; Howard, Andrew W.; Bai, Yu; Cabrera-Lavers, Antonio; Lu, Youjun; Zhang, Haotong; Justham, Stephen; Belczynski, Krzysztof; Wang, Xiaofeng; Corradi, Romano; Zhang, Jujia; Zhang, Tianmeng; Gu, Wei-Min; Wang, Song; Casares, Jorge; Gao, Qing; Yuan, Hailong; Bai, Zhongrui; Wang, Junfeng; Zheng, Chuanjie; Shao, Yong; Liao, Shilong; Qi, Zhaoxiang; Isaacson, Howard; Di Stefano, Rosanne; Rebolo, Rafael; Zheng, Zheng; Ren, Juanjuan; Wu, Jianfeng; Zhao, Yongheng; Wang, Huijuan; Zhang, Lan; Cui, Kaiming; Wang, Yilun; Wang, Tinggui; Cui, Xiangqun; Liu, Qingzhong; Heger, Alexander; Dong, Yiqiao; Chu, Yaoquan; Lei, Yajuan; Lattanzi, Mario; Zhang, Junbo; Bregman, Joel; Shao, Lijing; Zhang, Wei; Li, Xiangdong; Shen, Rongfeng; Mu, Xiaoyong
China, United States, Australia, Netherlands, Poland, Spain, Italy
Abstract
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 Sun1-4. Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star-black-hole binaries5,6. 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.