What were the very first stars like, and can we still see them?

Right after the Big Bang, the universe was almost pure hydrogen and helium, with barely a trace of anything heavier. The very first stars to form out of that gas, called population III stars, had none of the heavier elements (astronomers call anything past helium a 'metal') that later stars are built from. That absence is thought to have let them grow enormous, hundreds of times the Sun's mass, and burn through their fuel fast.

Those giant first stars likely lived short, violent lives. Many are thought to have ended in pair-instability supernovae, some of the most energetic explosions physics allows, scattering the first heavy elements, up to iron, out into space, to be recycled into the next generation of stars. The light these stars gave off is also thought to have started reionizing the universe: splitting the neutral hydrogen gas that filled the 'dark ages' back into charged plasma, and ending a long stretch when there were no visible-light photons anywhere.

Here's the catch: nobody has directly seen a single population III star. Everything we think we know about them comes from computer models of how such stars would have formed and died. The closest thing to evidence is indirect: a 2015 study reported signs consistent with them in a distant galaxy, and measurements of the universe's oldest light suggest the first stars formed roughly 300 million years after the very beginning.

That's exactly why the James Webb Space Telescope was built the way it was. It can see objects 100 times fainter than Hubble, and look back further in time, to within about 180 million years of the Big Bang, right around when the very first stars are thought to have switched on. Catching their light would finally test what the models say about the universe's first stars.