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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.sup.1-4. Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star-black-hole binaries.sup.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 H[alpha] emission line require the presence of a dark companion with a mass of [Formula omitted] 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., Author(s): Jifeng Liu [sup.1] [sup.2] [sup.3] , Haotong Zhang [sup.1] , Andrew W. Howard [sup.4] , Zhongrui Bai [sup.1] , Youjun Lu [sup.1] [sup.2] , Roberto Soria [sup.2] [sup.5] , [...]

Author(s): Jifeng Liu [sup.1] [sup.2] [sup.3] , Roberto Soria [sup.2] [sup.4] , Zheng Zheng [sup.5] , Haotong Zhang [sup.1] , Youjun Lu [sup.1] [sup.2] , Song Wang [sup.1] , Hailong [...]

Black-hole accretion states near or above the Eddington luminosity (the point at which radiation force outwards overcomes gravity) are still poorly known because of the rarity of such sources. Ultraluminous X-ray sources (1) are the most luminous class of black hole ([L.sub.x] ≅ [10.sup.40] erg [s.sup.-1]) located outside the nuclei of active galaxies. They are likely to be accreting at super-Eddington rates, if they are powered by black holes with masses less than 100 solar masses. They are often associated with shock-ionized nebulae (2,3), though with no evidence of collimated jets. Microquasars with steady jets are much less luminous. Here we report that the large nebula S26 (ref. 4) in the nearby galaxy NGC 7793 is powered by a black hole with a pair of collimated jets. It is similar to the famous Galactic source SS433 (ref. 5), but twice as large and a few times more powerful. We determine a mechanical power of around a few [10.sup.40] erg [s.sup.-1]. The jets therefore seem [10.sup.4] times more energetic than the X-ray emission from the core. S26 has the structure of a Fanaroff-Riley type II (FRII-type) active galaxy: X-ray and optical core, X-ray hot spots, radio lobes (6) and an optical and X-ray cocoon. It is a microquasar where most of the jet power is dissipated in thermal particles in the lobes rather than relativistic electrons., The very large, shock-ionized nebulae (ultraluminous X-ray source (ULX) bubbles (7)), with characteristic sizes of ~100-500 pc and ages of around a few [10.sup.5] yr are much larger and more [...]