Avi Loeb, a Harvard astrophysicist, has suggested that the interstellar object 3I/ATLAS could contain antimatter, which he describes as "the most efficient fuel" in the universe.
"the most efficient fuel" in the universe
Loeb proposes that the interaction between antimatter and solar particles could explain the object's unusual brightness and apparent acceleration. He also suggests that if 3I/ATLAS contains antimatter, its passage through the solar wind might generate detectable gamma-ray or X-ray emissions, which could be observed by NASA's Fermi Gamma-Ray Space Telescope.
Author's summary: Avi Loeb suggests 3I/ATLAS may contain antimatter.