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Detection of the Cosmic Gamma Ray Horizon: Measures All the Light in the Universe Since the Big Bang.

May 24, 2013 — How much light has been emitted by all galaxies since the cosmos began?

After all, almost every photon (particle of light) from ultraviolet to far infrared wavelengths ever radiated by all galaxies that ever existed throughout cosmic history is still speeding through the Universe today.

If we could carefully measure the number and energy (wavelength) of all those photons -- not only at the present time, but also back in time -- we might learn important secrets about the nature and evolution of the Universe, including how similar or different ancient galaxies were compared to the galaxies we see today.

That bath of ancient and young photons suffusing the Universe today is called the extragalactic background light (EBL).

An accurate measurement of the EBL is as fundamental to cosmology as measuring the heat radiation left over from the Big Bang (the cosmic microwave background) at radio wavelengths.

A new paper, called "Detection of the Cosmic γ-Ray Horizon from Multiwavelength Observations of Blazars," by Alberto Dominguez and six coauthors, just published today by the Astrophysical Journal -- based on observations spanning wavelengths from radio waves to very energetic gamma rays, obtained from several NASA spacecraft and several ground-based telescopes -- describes the best measurement yet of the evolution of the EBL over the past 5 billion years.