Although predicted by theory, none had been found until the observations leading to the discovery were performed with telescopes at the Observatorio del Roque de los Muchachos in the Canary Islands, the University of Barcelona reported Thursday.
The newly discovered black hole orbits the Be star known as MWC 656, located 8,500 light years from Earth.
Be-type stars are quite common across the Universe, the astronomers said.
"Their distinctive property is their strong centrifugal force: they rotate very fast, close to their break-up speed," Jorge Casares of the Instituto de Astrofisica de Canarias said.
In our Milky Way Galaxy alone more than 80 of them are known in binary systems together with neutron stars.
But MWC 656's companion was something different, the scientists said.
"It turned out to be an object with a mass between 3.8 and 6.9 solar masses," Ignasi Ribas of the Instituto de Ciencias del Espacio said. "An object like that, invisible to telescopes and with such large mass, can only be a black hole, because no neutron star with more than three solar masses can exist."