I went to a lecture yesterday given by Prof Bernard Pagel on neutrinos and we briefly touched on young galaxies, notable 1 Zwicky 47 which is around 500 million years old and he remarked that the metallicity of the stars were pretty much zero - I briefly discussed with him that I cannot accept that there were huge blobs of primordial matter, from the Big Bang, that was still unseeded by elements higher than Li. He agreed that this was a mystery and that maybe there was some other answers, like all that we see are very large, very old white stars mixed in with small amounts of 2nd & 3rd gen stars.
I cannot see how a large and very old white star could remain on the HR diagram without long ago supernovaing or cooling to form neutron stars or whatever....
Any ideas? Because he sure didn't!