The first stars ignite

Clouds of pristine hydrogen and helium collapse until their cores are hot enough to fuse, ending the Cosmic Dark Ages. These Population III stars have no elements heavier than lithium — nothing exists yet to make them from — which makes them enormous, blisteringly hot and short-lived, some hundreds of times the mass of the Sun. None has ever been observed directly; their existence is inferred from theory and from the chemistry of the oldest stars that followed.