Apparently, in the early universe, stars were massive - ranging up to about 500 solar masses. Furthermore the metallicity (elements other than H, He) in the early universe was effectively zero with only hydrogen, helium and trace amounts of lithium. Apparently, stars could reach large masses because much larger quantities of these H, He had to accumulate before they could come together and form a star. I was wondering if anyone knows an intuitive explanation for this? Or knows any equations which could explain this?