The first stars in the universe have a very unique property: the matter from which they form consists only of hydrogen, helium, and some traces of lithium, but essentially nothing heavier. All later generations, including present stars, are very different, polluted by the ashes of the first generation. This deficiency in heavier elements, "metals", dominates the whole life of these stars. Current numerical simulations indicate that they might have been much heavier than modern stars, indeed, real "heavy weights" of hundreds of solar masses or more could have been frequent among them. These very massive stars are rare today, and those we observer lose mass at such a high rate that they will have shrunk to "normal size" when they die. We now believe that the mass loss in the first stars was much less, maybe negligible. This allows for special evolutionary paths: for example, stars of a few hundred solar masses can encounter the electron-positron pair creation instability and entirely disrupt in explosions that may reach a hundred times the kinetic energy of typical supernova today. With upcoming generations of space telescopes we might be able to observe these events despite their being as distant as a redshift of twenty. Even without observing these explosions, a different approach to test our understanding of the first stars is to study the composition of their ashes, on which new stars have formed. Some very old stars, only recently observed in the halo of our galaxy, are assumed to consist mostly of such compositions, giving us additional clues on the fate of the first stars.
References| Katrin Heitmann / LANL / heitmann@lanl.gov / revised January 20 | |