Astronomers are reaching ever further back in time, seeking
events from the earliest days of the universe. Now, the
discovery of the farthest (and thus oldest) supernova ever seen
is raising hopes that astronomers will soon detect the explosive
deaths of the first stars to form after the universe's birth.
These stars forged the first heavy elements, which helped create
smaller and longer-lived stars like our own sun. The earliest
stars looked different from modern stars. The big bang produced
only three light elements—hydrogen, helium, and a little
lithium—but today, stars form in gas clouds that also contain
heavier elements such as carbon and oxygen. These elements
radiate away enough energy to eventually cool the clouds. When
the clouds cool, they fragment into smaller clumps that collapse
to spawn a plethora of mostly small stars. But such
fragmentation wasn't easy early in the universe's life, when
stars formed from carbon- and oxygen-free gas clouds that
remained warm. Because of their warmth, more grav