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. Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star–black-hole binaries. When the black hole is not accreting gas, it can be found through radial-velocity measurements of the motion of the companion star. We report here radial-velocity measurements taken over two years of the Galactic B-type star, LB-1. The star was initially discovered during a monitoring campaign with the 4-m telescope LAMOST and subsequently studied in more detail with the 10-m class telescopes GTC and Keck. We find that the motion of the B star and a superimposed Hα emission line (see figure) require the presence of a dark companion with a mass of 68 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. For comparison, black holes detected in X-ray binaries have masses in the range 5-15 solar masses. On the other hand, gravitational-wave experiments have detected black holes with several tens of solar masses. However, the formation of a ~70 solar mass black hole in a high-metallicity environment is extremely challenging within current stellar evolution theories. This would require a significant reduction in wind mass-loss rates and overcoming the pair-instability supernova phase, which limits the maximum black hole mass to less than ~50 solar masses. Alternatively, the black hole in LB-1 might have formed after a binary black hole merger or other exotic mechanisms.
It may interest you
-
Researchers at the Instituto de Astrofísica de Canarias (IAC) and the University of La Laguna (ULL), publish today in the journal Astronomy & Astrophysics the first results of a detailed study of nearly a thousand blue supergiants in the Milky Way. This is the biggest sample of stars of this type which has been studied until now. The study has used over 15 years of high quality observations taken mainly with the NOT and Mercator telescopes at the Roque de los Muchachos Observatory in La Palma. The analysis of these data will allow researchers to improve their knowledge of the evolution ofAdvertised on
-
It is well known that fullerenes – big, complex, and highly resistant carbon molecules with potential applications in nanotechnology – are mostly seen in planetary nebulae (PNe); old dying stars with progenitor masses similar to our Sun. Fullerenes, like C60 and C70, have been detected in PNe whose infrared (IR) spectra are dominated by broad unidentified IR (UIR) plateau emissions. The identification of the chemical species (structure and composition) responsible for such UIR emission widely present in the Universe is a mystery in astrochemistry; although they are believed to be carbon-richAdvertised on
-
Red dwarfs are the most common stars in the galaxy. In recent years they have become key targets in the search for exoplanets. These stars are usually accompanied by rocky planets and due to their low brightness, their habitable zone is close to the star, making it easier to find planets that are within it. GJ 1002 is a red dwarf just one-eighth the mass of the Sun, located only 15.8 light-years away. Using radial velocity measurements from the ESPRESSO and CARMENES spectrographs, we have discovered the presence of two Earth-like and potentially habitable planets. The planets, GJ 1002 b andAdvertised on