In a surprising twist, astronomers recently discovered an excess of gamma rays with energies of about a trillion electronvolts (TeV) emanating from the Sun. This finding puzzled scientists because it was previously thought that rare circumstances were needed to emit such high-energy gamma rays. This discovery challenges our understanding of how something so powerful could be produced by a relatively quiet, middle-aged star like the Sun.
Understanding gamma rays and their detection
Gamma rays are a type of high-energy electromagnetic radiation that is emitted by various celestial objects, including supernovae and star-forming regions. They have the highest energy levels in the electromagnetic spectrum and are known to be dangerous to living organisms. Fortunately, the Earth’s atmosphere acts as a shield, preventing gamma radiation from reaching the Earth’s surface.
To study gamma rays, astronomers use specialized satellites capable of recording energies up to 200 billion electron-volts. However, indirect methods are required to detect gamma rays with energies above this range. When high-energy gamma rays enter the upper atmosphere, they create a cascade of lower-energy particles and photons that fly in the same direction. When these particles pass through water, they produce a phenomenon called Cherenkov radiation, which can be observed in pitch black conditions.
Astronomers track this Cherenkov radiation using several tanks of water placed next to each other. If several tanks begin to glow at the same time, this indicates the presence of a gamma-ray flux and allows scientists to determine its energy and source.
Until now, our knowledge of high-energy gamma rays has come mainly from studying distant celestial objects. Extreme environments such as supernovae or star-forming regions were assumed to be the source of such powerful gamma rays. Therefore, little attention was paid to the study of gamma radiation emitted by our Sun.
However, Dr. Mehr Un Nisa of Michigan State University and her colleagues decided to pursue further research using the High Altitude Water Cherenkov Observatory (HAWC). To their amazement, they found a significant excess of gamma rays in the TeV range coming from the Sun. ‘After examining six years of data, the gamma ray excess was detected,’ says Dr. Nisa. “When we first saw it, we thought, ‘We’re definitely on to something. The Sun can’t be that bright at these energies.” HAWC detected seven times more radiation in this range than the highest estimates.
Further analysis confirmed the accuracy of the findings. The Sun was found to emit gamma rays at energies approaching 10 TeV, although no evidence of radiation above that level was observed.
Implications and future research
The detection of high-energy gamma rays from the Sun challenges our understanding of stellar physics. It was previously thought that the Sun could only produce gamma rays in the TeV range by interacting with cosmic rays from more powerful sources. However, the abundance of these gamma rays suggests that our star is capable of generating them on its own.
“The Sun is turning out to be more surprising than we thought,” Dr. Nisa remarked. “We thought we had this star figured out, but that turned out not to be the case.”
Scientists now face the challenge of unraveling the mechanisms behind the phenomenon. Further research and observations will be needed to determine how and why the Sun emits such high-energy gamma rays and what impact they may have on our understanding of stellar evolution.