A group of international researchers has discovered the highest-energy light ever observed from the sun.
In a new paper published last week in the journal Physical Review Letters, scientists found the star had emitted surprisingly bright gamma rays that had an energy level of about 1 trillion electron volts, or one tera electron volt (TeV).
Gamma rays are wavelengths of light that are known to carry the most energy of any other wavelength in the electromagnetic spectrum.
"The sun is more surprising than we knew," Mehr Un Nisa, a postdoctoral research associate at Michigan State University and the corresponding author, said in a release. "We thought we had this star figured out, but that’s not the case."
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Nisa works with the High-Altitude Water Cherenkov Observatory — a key part of this discovery — located between two dormant volcano peaks in Mexico.
Although the high-energy light doesn't reach the Earth's surface, the gamma rays create signatures that Nisa and her colleagues detected.
"In this particular energy regime, other ground-based telescopes couldn’t look at the sun because they only work at night," she explained. "Ours operates 24/7."
From its position, 13,000 feet above sea level, the observatory can witness the aftermath of gamma rays striking air in the atmosphere, with collisions resulting in "air showers."
Air showers are like particle explosions that the naked eye cannot see. The energy of the ray is "liberated and redistributed amongst new fragments consisting of lower energy particles and light," Michigan State University notes. And those particles created on the way down are what the observatory can "see."
When those particles interact with water in its tanks, they create Cherenkov radiation that can be detected with the observatory’s instruments.
Following six years of data collection, Nisa said an "excess of gamma rays" popped out.
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"When we first saw it, we were like, ‘We definitely messed this up. The sun cannot be this bright at these energies,'" she recalled.
The brightness and the amount of gamma rays were more than previously anticipated.
The university notes that researchers previously hypothesized it would be rare to see gamma rays reach Earth. However NASA's Fermi Gamma-ray Space Telescope mission showed there were about seven times more of the rays than initially expected. Notably, the telescope's measurements of the sun's gamma rays maxed out at around 200 billion electron volts.
Ohio State University professors John Beacom and Annika Peter encouraged the observatory's international collaboration to take a look.
"They nudged us and said, ‘We’re not seeing a cutoff. You might be able to see something,'" Nisa said.
Now, for the first time, the team has shown that the energies of the sun’s rays extend into the tera electron volts range, up to nearly 10 TeV, Nisa said. She noted that level does appear to be the maximum.
She said solar scientists will now ask how these gamma rays achieve such high energies and what role the sun’s magnetic fields play.
