Diffuse extragalactic background radiation

It contains photons whose energies span more than twenty orders of magnitude, from 10−7 eV to more than 100 GeV.

This range covers everything from the microwaves emitted by free hydrogen atoms to ultra high-energy gamma rays, which can only be emitted by the most powerful physical processes in the modern universe such as kilonovas and merging black holes.

The nature and history of the universe is coded in this radiation field and any realistic cosmological model must be able to describe it.

Understanding the DEBRA is a major challenge of modern cosmology with huge consequences in other fields of astrophysics, therefore extraordinary efforts are being put by theoreticians, observers, and instrumentalists to do so.

The overall diffuse extragalactic radiation field may be divided in different regions according to their origin and physical processes involved.