Published on July 20, 2017
This animation tracks several gamma rays through space and time, from
their emission in the jet of a distant blazar to their arrival in
Fermi’s Large Area Telescope (LAT). During their journey, the number of
randomly moving ultraviolet and optical photons (blue) increases as
more and more stars are born in the universe. Eventually, one of the
gamma rays encounters a photon of starlight and the gamma ray
transforms into an electron and a positron. The remaining gamma-ray
photons arrive at Fermi, interact with tungsten plates in the LAT, and
produce the electrons and positrons whose paths through the detector
allows astronomers to backtrack the gamma rays to their source.
