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Scientists have now traced all the starlight across
ninety percent of cosmic history, thanks to NASA's Fermi Gamma-ray
Space Telescope. Fermi studies the universe using gamma rays,
the highest-energy form of light. Over the last 10 years,
Fermi has measured gamma rays from nearly 2,000 blazars.
These galaxies host supermassive black holes and produce
jets of high-speed particles. Gamma rays from these blazars
interact with starlight produced throughout the cosmos. Even after
stars burn out, their light continues to travel across the universe,
forming the extragalactic background light, or EBL.
When a gamma ray collides with starlight, it transforms into two
particles, an electron and a positron, in accordance with Einstein's
famous equation. These collisions weaken a blazar's gamma-ray
signal like fog dulling a car's headlights. The further back scientists
look, the greater the EBL's dimming effect. A new study
of the EBL peered back through 12 billion years of starlight,
confirming that star formation in our universe peaked about
10 billion years ago. Stars create most of the light in the universe
and many of its heavy elements, like silicon and iron.
Understanding how our cosmos came to be depends in large part on
understanding how stars evolved. Thanks to Fermi,
we're one step closer. [Music]
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