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.
a) radial velocity curves and orbital fits for the B-star (purple) and its dark companion (orange), the latter extracted from the wings of the Hα emission (panel c). b) Residuals obtained after subtracting the best orbital models from the velocity points.
It may interest you
-
An international study led by Almudena Prieto, a researcher at the Instituto de Astrofísica de Canarias (IAC) has found places where new stars are forming, as faint star clusters, around the centre of an evolved galaxy. This is the first time that young populations of stars have been picked out and dated in this type of galaxies dominated by very old stars, which can be called “rejuvenated old galaxies”. The research has combined observations from various telescopes, both ground based and space based, and has used innovative techniques of data analysis. The results are published in theAdvertised on
-
The Solar System research group at the Instituto de Astrofísica de Canarias (IAC) is participating in the international programme to keep a closet track of asteroid 2024 YR4. The aim is to determine its orbit with the highest possible precision before it stops being observable by ground based and satellite telescopes in April, and so improving our value of the probability that it will impact the Earth in 2032. In this context several telescopes of the Canary Observatories of the IAC are playing an outstanding role in this observing campaign: The Gran Telescopio Canarias (GTC) at the Roque deAdvertised on
-
The existence of dark matter is probably one of the fundamental mysteries of modern science and unraveling its nature has become one of the primary goals of modern Physics. Despite representing 85% of all matter in the Universe, we do not know what it is. In its simplest description, it is made up of particles that interact with each other and with ordinary matter only through gravity. However, this description does not correspond to any physical model. Finding out what dark matter is requires finding evidence of some kind of interaction of dark matter that goes beyond gravity. In our workAdvertised on