Free Astronomy Magazine May-June 2022

MAY-JUNE 2022 Today we know that many of them have existed for over 10 billion years and that some are almost as old as the universe itself. However, not even the oldest known stars can be- long to the first generation of stars born in the universe. In fact, even if the metals of Population II are not very abundant, most of those metals still did not exist immediately after the Big Bang, when the universe was composed almost entirely of hy- drogen and helium, with negligible traces of lithium and beryllium. It was to fill this gap that astronomers introduced a hypothetical third class of stars, Population III, whose chem- ical composition should mirror that of the primordial gas generated di- rectly by the Big Bang. While the search has been on for decades, no Population III stars have so far been observed with certainty. The most shared explanation by as- tronomers for this is that all Popula- tion III stars must have had enor- mous masses, at least 50-300 solar masses, since star formation models indicate that lower metallicity re- quires a greater initial mass for the