Washington: The evolution of the extragalactic background light (EBL) over the past 5 billion years has been measured for the first time.
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 study by Alberto Dominguez and six coauthors -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.
Directly measuring the EBL by collecting its photons with a telescope, however, poses towering technical challenges-harder than trying to see the dim band of the Milky Way spanning the heavens at night from midtown Manhattan.
Earth is inside a very bright galaxy with billions of stars and glowing gas. Indeed, Earth is inside a very bright solar system: sunlight scattered by all the dust in the plane of Earth`s orbit creates the zodiacal light radiating across the optical spectrum down to long-wavelength infrared. Therefore ground-based and space-based telescopes have not succeeded in reliably measuring the EBL directly.
So, astrophysicists developed an ingenious work-around method: measuring the EBL indirectly through measuring the attenuation of-that is, the absorption of-very high energy gamma rays from distant blazars. Blazars are supermassive black holes in the centers of galaxies with brilliant jets directly pointed at us like a flashlight beam.
This latest result confirms that the kinds of galaxies observed today are responsible for most of the EBL over all time. Moreover, it sets limits on possible contributions from many galaxies too faint to have been included in the galaxy surveys, or on possible contributions from hypothetical additional sources (such as the decay of hypothetical unknown elementary particles).
The research is published in the Astrophysical Journal.