The Sun's high-energy radiation was seven times more abundant than thought, new research has found.

In 2019, a puzzling discovery left astronomers scratching their heads about the sun. After a decade of observations, researchers found that the sun's high-energy radiation was seven times more abundant than anticipated. A recent study, based on even higher-energy data, has provided further insights into this solar mystery. The research, conducted by the High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory and its collaborators, reveals that the excess of solar gamma radiation persists at higher energies before declining at the topmost energies explored. This enigmatic phenomenon remains unexplained, leaving scientists intrigued.

One leading hypothesis centers on cosmic rays—high-energy particles originating from events like supernovas and black hole collisions. These cosmic rays interact with the sun's magnetic fields, which capture and redirect them outward. As cosmic rays collide with protons in the sun's atmosphere, they generate unstable particles called pions, leading to the production of gamma rays. However, not all of these gamma rays escape the sun.

The new findings suggest that cosmic rays in a specific energy range are "mirrored" by the sun's magnetic field lines. These cosmic rays enter and, on their way out, collide with protons to produce gamma rays. This hypothesis aligns with observations showing that the gamma-ray signal is strongest during the solar minimum, a phase when the sun's magnetic field is weakest. However, there remains a question of a potential cutoff in the data—above a certain energy, gamma rays might disappear, offering insights into the nature of this excess.

Researchers employed the HAWC experiment, a ground-based observatory near Puebla, Mexico, to explore gamma rays more than ten times more energetic than previous studies. The results indicated a cutoff effect, where the signal strength dropped off with increasing energies, providing a vital energy scale to model the sun's gamma-ray radiation. However, the cause of this cutoff and the persistence of the unusual signal at high energies remain mysteries, challenging existing models.

The study also did not address a perplexing narrow dip in the gamma-ray signal at specific frequencies. Researchers are working on extensive simulations of the sun's magnetic fields and cosmic particle dynamics to unravel this mystery. Beyond solving the gamma-ray puzzle, scientists believe that HAWC measurements could offer insights into solar and particle physics, providing a new laboratory to explore uncharted regions of the sun and study new physics.