Hydrogen, helium, and a minuscule trace of lithium are the only elements left over from the first minutes after the Big Bang, 13.7 billion years ago. The creation of all heavier elements, collectively called “metals” in astrophysicists’ shorthand, had to await the coming of the first stars a few hundred million years later. So first-generation stars formed from pristine clouds of H and He. Only with their deaths was the cosmos first seeded with the metals they created.
So goes the standard theory of Big Bang nucleosynthesis (BBN). It’s been impressively confirmed by the agreement between the predicted and measured cosmic abundance ratios of the various H and He isotopes (see PHYSICS TODAY, August 1996, page 17). But despite its general acceptance, the BBN scenario has come up against some frustrating nonobservations. No first-generation stars have yet been seen. Nor, until now, have observers found any intergalactic gas cloud...
