The diffuse extragalactic background radiation (DEBRA) refers to the photon field of extragalactic origin that fills our Universe. 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 Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...

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 origin and the physical processes involved are different within every wavelength range. There is plenty of observational evidence that support the existence of the DEBRA. The figure shows a schematic picture, based on many different data sets, of the spectral intensity (also called spectral radiance) multiplied by wavelength of the DEBRA over all the electromagnetic spectrum. This representation is convenient because the area inside the curve is the energy. 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.

Regions of the DEBRA

The overall diffuse extragalactic radiation field may be divided in different regions according to their origin and physical processes involved. This is a standard classification from the highest down to the lowest energies: *

Diffuse extragalactic gamma-ray radiation Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemica ...

(also known as

cosmic gamma-ray background Cosmic commonly refers to: * The cosmos, a concept of the universe Cosmic may also refer to: Media * ''Cosmic'' (album), an album by Bazzi * Afro/Cosmic music In music, the terms Afro/cosmic disco, “Looking over to the blogosphere, the ...

) *

Cosmic X-ray background The observed X-ray background is thought to result from, at the "soft" end (below 0.3 keV), galactic X-ray emission, the "galactic" X-ray background, and, at the "hard" end (above 0.3keV), from a combination of many unresolved X-ray sources outsid ...

Extragalactic background light The diffuse extragalactic background light (EBL) is all the accumulated radiation in the universe due to star formation processes, plus a contribution from active galactic nuclei (AGNs). This radiation covers almost all wavelengths of the electromag ...

(which includes the cosmic infrared background) *

Cosmic microwave background In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...

Cosmic radio background Cosmic commonly refers to: * The cosmos, a concept of the universe Cosmic may also refer to: Media * ''Cosmic'' (album), an album by Bazzi * Afro/Cosmic music In music, the terms Afro/cosmic disco, “Looking over to the blogosphere, the ...

References

External links

Caltech papers
Extragalactic astronomy Cosmic rays Cosmic background radiation Unsolved problems in astronomy {{Astrophysics-stub