How did a photon survive a journey of more than 2 billion light-years when, according to known physics, it should have been absorbed long before reaching Earth? This is the question at the heart of a new study by Giorgio Galanti (INAF) and Marco Roncadelli (INFN), accepted for publication in Physical Review Letters.

The research addresses one of the most fascinating puzzles in contemporary astrophysics. It proposes a possible explanation for the highest-energy photon ever observed from a gamma-ray burst, suggesting that under extreme conditions spacetime may behave differently from what Einstein’s theory of relativity predicts.

At the center of the story is the brightest gamma-ray burst ever observed, GRB 221009A, nicknamed BOAT by astronomers—the Brightest Of All Time. The explosion, which occurred about 2 billion light-years from Earth and was observed on Oct. 9, 2022, reached our planet as an enormous shower of photons, the elementary particles of light.