Can Population III stars generate primordial helium?

Only stars with masses in excess of M_c∼200 M _⊙ can generate a cosmologically significant amount of helium^1-3 without overproducing either metals^2,3 or radiation². Such very massive objects (VMOs) would also leave a large number of black hole remnants. Recent stellar evolution calculations ^4,5 show that the helium-rich envelope of VMOs could undergo explosive ejection. We describe here a viable model of primordial helium synthesis which can be constructed after recombination, providing heavy elements are not dredged up and ejected at the same time.