When the Sun unleashes its most violent eruptions, known as solar flares, it floods space with intense radiation, including powerful gamma rays.
For decades, scientists have detected these signals but struggled to explain exactly where they come from. Now, solar physicists say they have finally solved this long-standing mystery.
In a new study published in Nature Astronomy, researchers from New Jersey Institute of Technology’s Center for Solar-Terrestrial Research report the discovery of a previously unknown source of high-energy particles in the Sun’s atmosphere.
These particles, they say, are responsible for producing the intense gamma rays observed during major solar flares.
The team focused on a powerful X8.2-class solar flare that erupted on September 10, 2017. During this event, they detected an enormous concentration of particles in the Sun’s upper atmosphere, known as the corona.
These particles reached energies of several million electron volts, making them hundreds to thousands of times more energetic than typical flare particles and fast enough to move close to the speed of light.
According to the researchers, these extreme particles generate gamma rays through a process called bremsstrahlung. In simple terms, this happens when lightweight charged particles, such as electrons, slam into material in the Sun’s atmosphere and release high-energy light.
“We knew solar flares produced a distinctive gamma-ray signal, but the data alone didn’t tell us where it came from or how it formed,” said lead author Gregory Fleishman. “By combining different types of observations, we were finally able to track down the source.”
To do this, the team merged data from two powerful instruments. NASA’s Fermi Gamma-ray Space Telescope provided detailed measurements of gamma rays from the flare, while NJIT’s Expanded Owens Valley Solar Array supplied high-resolution microwave images that reveal where energetic particles are located in the corona.
By comparing these datasets, the researchers identified a previously unrecognized region in the solar atmosphere where gamma-ray and microwave signals overlapped. This region contained a strange population of particles unlike those normally seen in solar flares. Instead of having many low-energy particles and fewer high-energy ones, this group was dominated by extremely energetic particles.
Advanced computer models showed that the energy pattern of these particles matched the observed gamma-ray signals, confirming that bremsstrahlung was the missing mechanism scientists had been searching for. The location of the particles also fits with long-standing theories suggesting that solar flares release stored magnetic energy to accelerate particles to extreme speeds.
Many questions remain, including whether these particles are electrons or their antimatter counterparts, positrons. Future upgrades to the solar array, led by co-author Bin Chen, are expected to provide new clues.
By filling a major gap in solar flare physics, the discovery could improve models of solar activity and help scientists better predict space weather events that can affect satellites, astronauts, and power systems on Earth.
Source: KSR.
