NJIT Physicists Confirm Gamma-Ray Generation Mechanism in Intense Solar Flares

Solar physicists at the New Jersey Institute of Technology’s Center for Solar-Terrestrial Research (NJIT-CSTR) have achieved a major breakthrough in understanding the most violent events on the Sun. They have definitively pinpointed the origin of the powerful gamma-ray emissions observed during major solar flares. This significant finding, recently published in the journal Nature Astronomy, resolves a long-standing scientific puzzle concerning the anomalous radiation signals detected during these intense solar outbursts.

The research focused specifically on the X8.2-class flare that erupted on September 10, 2017. Through meticulous data analysis, the team localized a concentration within the solar corona, specifically in what is termed Region of Interest 3 (ROI 3). This area contained trillions of particles energized to levels reaching several million electron volts (MeV). These particles were traveling at speeds approaching the speed of light, possessing energies hundreds to thousands of times greater than the typical particles released during standard solar flares. The researchers established that the primary mechanism producing the gamma radiation was bremsstrahlung, or 'braking radiation,' which occurs when these ultra-high-energy electrons collide with the material making up the solar atmosphere.

This crucial work involved leading experts, notably Physics Professor Gregory Fleishman, who served as the lead author, and Binchang Chen, Director of the Owens Valley Solar Array (EOVSA), who acted as a co-author. To secure such granular results, the team successfully integrated data streams from two distinct instruments. NASA’s Fermi Gamma-ray Space Telescope provided precise temporal tracking of the gamma-ray emissions, while the NJIT-developed Extended Owens Valley Solar Array (EOVSA), a ground-based radio interferometer, offered microwave imagery sensitive to the presence of these accelerated electrons.

This confirmation validates long-held theories suggesting the Sun is capable of efficiently accelerating charged particles to extreme energies by tapping into stored magnetic energy. According to Gregory Fleishman, this scientific milestone is set to substantially refine current models of solar activity, thereby improving the accuracy of space weather forecasting. The necessity for such improvements has been underscored by recent phenomena, such as the powerful geomagnetic storm observed in May 2024, which was linked to the active region designated NOAA 13664.

The next critical phase for the research team involves discerning the precise composition of these extreme particle populations—specifically, separating the contribution of electrons from that of positrons. To tackle this challenge, plans are underway to upgrade the EOVSA facility to the EOVSA-15 configuration, with completion anticipated in 2026. This enhanced capability will permit measurements of microwave polarization, which should finally resolve the nature of these high-energy particles. While the Sun’s 28-day rotation imposes limitations on continuous observation, this constraint was partially mitigated in 2024 by supplementary data gathered by the European Space Agency’s Solar Orbiter spacecraft during its observations of NOAA 13664.