In a groundbreaking discovery, solar physicists detected the most energetic light ever observed emanating from the sun, raising new questions about our home star's behavior.
The observation was made during a near decadelong campaign involving over 30 institutions across three continents - North America, Europe, and Asia, and it marked the first-ever detection of solar gamma radiation in the teraelectron volt (TeV) range.
The High Altitude Water Cherenkov (HAWC) observatory in Mexico proved instrumental in the discovery. HAWC is one of the few detectors capable of observing the sun in the TeV range, allowing continuous exposure as the sun moves across the sky.
"We now have observational techniques that weren’t possible a few years ago... In this particular energy regime, other ground-based telescopes couldn’t look at the sun because they only work at night. Ours operates 24/7," said Mehr Un Nisa, a post-doctoral research associate at Michigan State University and co-author of the study.
The data collected from 2014 to 2021 revealed emissions ranging from 0.5 to 2.6 TeV coming from the direction of the sun. Researchers concluded that an emission reading originated from the sun, with a 6.3 sigma probability.
While not the highest-energy light ever detected in space (that record belongs to gamma rays from the Crab Nebula), the findings are unprecedented for our own star.
Researchers speculate the TeV emission could be a result of galactic cosmic rays colliding with nuclei in the solar atmosphere. Similar to how cosmic rays interact with Earth's atmosphere to produce a gamma ray glow, a comparable process might be occurring on the sun.
However, the exact mechanism behind the phenomenon remains unknown and does not align with current theoretical models. It is suspected that the sun's messy magnetic fields may play a crucial role, possibly acting as accelerators for cosmic ray electrons to generate synchrotron gamma radiation.
Further modeling and research will be needed to fully comprehend the puzzling phenomenon. The observations underscored the necessity for a revised framework that can account for the anomalous excess of gamma rays from the sun, not only in the giga-electron volts range but also in the TeV range.
The research was published in the Physical Review Letters journal.