In the cosmos, the most-weakly-interacting particles may have the strongest presence. Dark matter particles are estimated to constitute more than 80% of the matter in the Universe, but are so weakly interacting with other matter that physicists have been unable to figure out what they are. Likewise, neutrinos are the most difficult to detect of the known particles, yet they are known to dominate the late stages of a star’s evolution and likely drive the supernova explosion that follows the core collapse of a dying massive star.
Within this particle landscape is the axion, a hypothetical spin-zero boson with very small mass that is considered a strong contender for dark matter. Axions have never been detected, but the theory that describes them predicts they are created when photons interact with magnetic fields or electric charges—a condition overwhelmingly met in stars. Since this process would drain energy from stars, astrophysicists can observe the evolution of stars to place bounds on the axion production rate. In Physical Review Letters, Alexander Friedland of Los Alamos National Laboratory, New Mexico, and colleagues use this argument to provide the strongest upper limit to date on the strength of the interaction between axions and electromagnetic fields. Their results provide feedback into theoretical models of axions and can be used to assess the sensitivity of axion detectors. On another level, their work highlights the role of stars as particle-physics laboratories, complementary to those on Earth.
(via Physics - Particle Physics in the Sky)