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 shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequencies between 300 MHz an ...
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:
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Diffuse extragalactic gamma-ray radiation (also known as
cosmic gamma-ray background)
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Cosmic X-ray background
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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 electrom ...
(which includes the
cosmic infrared background
Cosmic infrared background is infrared radiation caused by stellar dust.
History
Recognizing the cosmological importance of the darkness of the night sky (Olbers' paradox) and the first speculations on an extragalactic background light dates ...
)
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Cosmic microwave background
The cosmic microwave background (CMB, CMBR), or relic radiation, is microwave radiation that fills all space in the observable universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dar ...
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Cosmic radio background
See also
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Photon underproduction crisis
The photon underproduction crisis is a cosmological discussion concerning the purported deficit between observed photons and predicted photons.
The deficit, or underproduction crisis, is a theoretical problem, arising from comparing observations o ...
References
External links
Caltech papers
Extragalactic astronomy
Cosmic rays
Cosmic background radiation
Unsolved problems in astronomy
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