A few hundred million years after the Big Bang, the first stars ignited—literally the "let there be light" moment for the universe. Now known to astronomers as Population III, or Pop III, stars, these giants were very different from the stars we know today. They formed from pristine hydrogen and helium, with almost no "metal" (i.e., other elements) holding them back. They were also huge, growing to tens to hundreds of times larger than the sun. And they died young, in many cases collapsing into the universe's earliest black holes.