New photometry was acquired in 2008 from the Nordic Optical Telescope (NOT) and again in 2010 using both the NOT and WHT, and spectra were acquired from the Gran Telescopio Canarias (GTC). Due to the short integration time of the WHT images the astronomers were able to resolve an intense flickering which strongly dilutes the secondary star's ellipsoidal modulation. The object was about one magnitude brighter than in its quiescence state and showed flares with a time-scale of order 10 minutes and amplitudes of up to magnitude 0.5.
By combining the data taken using the INT and the WHT in 2000 with the photometry taken in 2008, an orbital period of 6.6 hours was derived. The spectra taken with the GTC gave a radial velocity of semi-amplitude 541 km/s. These values give a mass function of 4.5 solar masses which sets a lower limit to the mass of the compact object, therefore implying the presence of a black hole. The lack of eclipses and the depth of the minima in the light curve constrains the inclination of the system to be between 40° and 70°, giving a lower limit to the mass of the black hole of 5.42 solar masses.
There are ~20 dynamically confirmed binaries with black holes out of an estimated population of a few thousand in our Galaxy.
J. M. Corral-Santana, J. Casares, T. Shahbaz, C. Zurita, I. G. Martínez-Pais, P. Rodríguez-Gil, 2011, MNRAS, article first published online: 25 Feb 2011.
"Descubren un agujero negro de más de cinco veces la masa del Sol", IAC Press Release, 23/03/2011..
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