THE PHOTON THAT SHOULD NEVER HAVE ARRIVED ON EARTH

A very-high energy photon, as hish as 18 TeV, associated with the most powerful gamma-ray burst recorded so far, GRB 221009A, has challenged the current models that describe these very violent astrophysical events. An all-Italian group of researchers from the INAF National Institute for Astrophysics and the INFN tried to shed light on this unexpected observation, proposing an interpretation that envisages the presence of an oscillation between photons and ALPs, hypothetical particles predicted by string theory. According to the hypothesis presented in the article “Observability of the very-high-energy emission from GRB 221009A”, published on PRL Physical Review Letters on December 18, the 18 TeV photon could actually be a ‘transformer photon’, it can be capable of changing nature, oscillating from one ‘personality’ to another while traveling at the speed of light. And the ALPs would be one of these personalities (ALPs are axion-like particles, hypothetical candidate particles to constitute cold dark matter, similar to other hypothetical particles, axions). An ALP is in fact capable of carrying out actions that a photon would never be able to complete: crossing the so-called EBL, the extragalactic background light (the light emitted by all the stars during the entire evolution of the universe). To give solidity to this hypothesis, other observations will be needed, and for this reason the new high energy astrophysical observatories – first of all CTA and the Italian ASTRI – are ready to come into operation in the coming years will be of great help