Evidence of a supernova origin for the black hole in the system GRO J1655-40

Stars with masses greater than about ten solar masses are thought to end th eir lives either in a supernova(1) or in a direct gravitational collapse pr ocess(2), either of which could have a black hole as a remnant. But there i s as yet no direct observational evidence to support either gravitational c ollapse in general or the formation of black hole remnants in particular. H ere we report a large overabundance of oxygen, magnesium, silicon and sulph ur in the atmosphere of the star orbiting a probable black hole in the bina ry system GRO J1655-40 (also known as Nova Scorpii 1994), These alpha-eleme nts are six to ten times more abundant in the star's atmosphere than they a re in the Sun's. We interpret these high abundances as evidence for superno va ejecta captured by the companion star. The relative abundances of these elements suggest that the supernova progenitor was in the mass range 25-40 solar masses.