In addition to all the sources Fermi detects, the gamma-ray sky is filled with a diffuse glow from cosmic ray interactions with gas and dust between stars.
It's important to disentangle the diffuse interstellar emission from gamma-ray sources inside and outside of our Galaxy in order to find and accurately characterize them. Here's how we construct those maps.
Fermi revealed gigantic faint structures in the diffuse interstellar emission. This discovery and its relation to the Microwave Haze give us unique insight into the history of the Milky Way.
Over the last 10 years Fermi has revealed fascinating structures in the gamma-ray sky by collecting one photon at a time, now with >300 million and counting. We visualize how counting photons reveals sources and structures by representing Fermi photons with LEGO.