A detector buried deep in Antarctic ice has captured the first experimental evidence of a predicted but never-before-seen phenomenon: radio pulses generated when high-energy cosmic rays slam into the ice sheet and trigger particle cascades inside it. Through results published in Physical Review Letters, astronomers of the Askaryan Radio Array (ARA) Collaboration have validated a key technique, which they hope will eventually allow them to detect some of the rarest and most energetic particles in the universe.
In 1962, Soviet physicist Gurgen Askaryan predicted that high-energy particles passing through a dense material should produce a distinctive burst of radio waves. When such a particle strikes an atom, it triggers a cascade of secondary particles that sweeps up electrons from the surrounding material, creating a negatively charged shower front that radiates at radio frequencies.
This “Askaryan radiation” was later confirmed in lab experiments and detected in air, but observing it in ice proved far more challenging. This is partly due to the difficulty of distinguishing genuine signals from the many sources of radio noise in polar environments, and partly because the simulations needed to model the effect in ice have only recently become sophisticated enough to make such rigorous analysis possible.
