⚡ A new population of ultra-energetic particles discovered in the Sun

The Sun, which provides us with light and heat, is also the site of immense phenomena. In 2017, a powerful solar flare emitted gamma rays whose origin left astronomers puzzled. These emissions seemed to come from a particular area of the solar atmosphere, but their precise source remained unknown until today.

A team from NJIT's Center for Solar-Terrestrial Research has identified the origin of these radiations. By examining data from an X8.2-class burst, scientists have revealed a previously unknown population of particles in the solar corona. These particles reach energies of several million electronvolts, far higher than those usually encountered during flares. This discovery therefore lifts the veil on a previously unknown mechanism of our star.


To achieve this result, researchers combined observations from two instruments. NASA's Fermi space telescope measured the high-energy gamma rays, while the ground-based EOVSA radio array provided microwave images. The overlay of this data allowed them to isolate a specific region of the solar atmosphere, designated ROI 3. This method established a link between the energetic signals and a very specific local activity.

Within this zone, scientists detected a significant number of particles accelerated to speeds close to that of light. Unlike the classic electrons from flares, this new population shows a high concentration of very high-energy particles, with few low-energy electrons. This particular distribution made it possible to directly associate these particles with the captured gamma emissions.

The responsible mechanism, called bremsstrahlung or braking radiation, is itself well-known. It occurs when charged particles like electrons collide with matter, here the solar atmosphere, and thus release high-energy radiation. It is this process that generates the observed gamma rays, clarifying an unknown aspect of solar flare physics and putting an end to a scientific debate.

This advancement allows for a better understanding of how solar flares manage to accelerate particles to such extreme energy levels. It also facilitates the development of more effective models to predict space weather, which affects Earth's technological systems. Some points remain to be clarified, notably the exact nature of these particles, which could be electrons or positrons. Improved instruments such as EOVSA-15 will allow further progress.

According to Gregory Fleishman, lead author of the study published in Nature Astronomy, measuring the polarization of microwave emissions should allow differentiation between particle types.

Braking radiation (bremsstrahlung)

Braking radiation is a physical phenomenon where charged particles, like electrons, lose energy in the form of light when they are slowed down by an electric field, such as that of an atom. This process is common in the Universe; it explains why we observe X-rays or gamma rays in many cosmic events.

In the case of the Sun, during a flare, electrons are accelerated to very high speeds. As they pass through the dense solar atmosphere, they collide with other particles, which abruptly slows them down. This deceleration causes the emission of high-energy photons, i.e., gamma rays. This is how bremsstrahlung becomes a significant source of radiation in solar flares.

Understanding this mechanism helps scientists interpret the signals observed by telescopes. By linking the energy of the particles to the radiation spectra, they can deduce the physical conditions in the solar atmosphere. This allows them to improve theoretical models and better predict the Sun's behavior during extreme events.

Bremsstrahlung is not limited to the Sun; it also occurs in other environments, such as around black holes or in particle accelerators on Earth. Studying this phenomenon therefore offers keys to exploring various energetic processes in the Universe, simplifying difficult concepts to make them accessible.