  It has been proposed theoretically that the first generation of stars in the
Universe (population III) would be as massive as 100 solar masses (100Mo),
because of inefficient cooling of the precursor gas clouds. Recently, the most
iron-deficient (but still carbon-rich) low-mass star -- HE0107-5240 -- was
discovered. If this is a population III that gained its metals (elements
heavier than helium) after its formation, it would challenge the theoretical
picture of the formation of the first stars. Here we report that the patterns
of elemental abundance in HE0107-5240 (and other extremely metal-poor stars)
are in good accord with the nucleosynthesis that occurs in stars with masses of
20-130Mo when they become supernovae if, during the explosions, the ejecta
undergo substantial mixing and fall-back to form massive black holes. Such
supernovae have been observed. The abundance patterns are not, however,
consistent with enrichment by supernovae from stars in the range 130-300 Mo. We
accordingly infer that the first-generation supernovae came mostly from
explosions of ~ 20-130Mo stars; some of these produced iron-poor but carbon-
and oxygen-rich ejecta. Low-mass second-generation stars, like HE0107-5240,
could form because the carbon and oxygen provided pathways for gas to cool.
