Six decades after its discovery, the first black hole ever detected is still causing astronomers to scratch their heads. It turns out that the cosmic behemoth at the heart of the Cygnus X-1 system is 50% more massive than previously thought, making it the heaviest stellar-mass black hole ever observed directly.

Based on new observations, an international team of researchers estimate the black hole is 21 times the mass of our sun and spinning faster than any other known black hole. The recalculated weight is causing scientists to rethink how bright stars that turn into black holes evolve, and how fast they shed their skins before they die.