A wide star-black-hole binary system from radial-velocity measurements.
basic_science · Level V
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- Record sourced from PubMed, PMID 31776491.
- Also identified by DOI 10.1038/s41586-019-1766-2.
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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 Sun<sup>1-4</sup>. Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star-black-hole binaries<sup>5,6</sup>. 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 [Formula: see text] 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.