Extragalactic background light (EBL) is an incredibly important measurement for scientists trying to unravel the mysteries of our universe. An accurate documentation of EBL, however, has never been recorded - until now - and it proves that all galaxies visible today are the reason for all the light we see, ever.
EBL has been difficult to measure for the same reason it's hard to see stars through any significant light pollution. Our bright solar system and our bright galaxy tend to change the pathways of photons, meaning that using a traditional ground or solar telescope setup simply isn't enough. Instead, astrophysicists had to turn to an indirect method to measure EBL.
Enter blazars. These supermassive black holes can be found in the center of supermassive black holes spewing out massive gamma ray jets directly at us. These gamma rays, however, do not travel through the universe unimpeded.
"When a high-energy gamma ray photon from a blazar hits a much lower energy EBL photon, both are annihilated and produce two different particles: an electron and its antiparticle, a positron, which fly off into space and are never heard from again," explains a University of California press release. "Different energies of the highest-energy gamma rays are waylaid by different energies of EBL photons."
What this means is that by measuring the various energy levels of the blazar gamma rays shooting at us, researchers can determine EBL levels and how they've evolved over the past 5 billion years.
In the end, it doesn't give us a clear panorama of our universe, but the levels of EBLs observed means scientists don't have to worry about galaxies that might be too faint and too far away for us to see yet. What we can see, is all that ever was.
You can read the full published study in The Astrophysical Journal.
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