Gamma rays emanating from active galaxies



Astronomers have tracked gamma rays emanating from active galaxies called blazars (yellow ovals, right) to measure the extragalactic background light throughout the universe’s history. Even at great distances, the EBL washed out most of the gamma rays (top), suggesting that stars were already forming and spitting out photons during early eras.

Credit: Diagram: E. Otwell, Illustrattion: GSFC/NASA

via sciencenews


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