Gamma rays from solar flares sometimes last for hours because the processes that produce these high-energy photons can continue well beyond the initial explosive event, involving complex interactions of accelerated particles with the solar atmosphere and magnetic fields. Unlike the brief flash of visible light or X-rays during a flare, gamma-ray emission can be sustained by prolonged acceleration and trapping of energetic protons and ions, which then collide with the solar material to produce gamma rays over extended periods.
When a solar flare occurs, it releases a tremendous amount of energy, accelerating charged particles such as protons, electrons, and heavier ions to very high speeds. These energetic particles interact with the Sun’s atmosphere, producing gamma rays primarily through nuclear reactions—especially when high-energy protons collide with atomic nuclei, creating unstable particles that decay and emit gamma rays. This nuclear gamma-ray emission can persist as long as there are energetic protons present and interacting with the solar material.
One key reason gamma rays can last hours is that the accelerated protons do not immediately escape the Sun’s magnetic environment. Instead, they can become trapped in magnetic loops or structures above the solar surface, where they continue to spiral and collide with the dense solar atmosphere. This trapping delays their escape and prolongs the gamma-ray production. The magnetic fields act like a cage, holding these particles in place and allowing sustained interactions that emit gamma rays long after the initial flare’s peak brightness.
Additionally, some solar flares are associated with coronal mass ejections (CMEs), which are massive bursts of solar plasma and magnetic field ejected into space. These CMEs can drive shock waves that further accelerate particles over extended timescales. The shock-accelerated protons can then return to the Sun’s atmosphere or interact with the solar wind, producing gamma rays that last for hours or even longer.
The energy spectrum of these gamma rays often shows signatures consistent with proton and ion acceleration rather than just electron acceleration, indicating that nuclear processes dominate the prolonged emission. Observations have detected gamma rays in the range from tens of MeV up to several GeV during these extended phases, confirming the presence of very high-energy particles interacting with the Sun.
In some cases, gamma-ray emission has been observed from solar flares originating in active regions just beyond the visible edge of the Sun, suggesting that the accelerated particles can travel along magnetic field lines and produce gamma rays in regions not directly visible in other wavelengths. This further supports the idea that particle acceleration and gamma-ray production are complex, extended processes involving large-scale magnetic structures.
The duration of gamma-ray emission can also be influenced by the density and composition of the solar atmosphere where the particles interact. Denser regions provide more targets for collisions, sustaining gamma-ray production, while variations in magnetic field strength and configuration affect how long particles remain trapped.
In summary, gamma rays from solar flares last hours because the energetic protons and ions responsible for their production are trapped and continuously accelerated by the Sun’s magnetic fields and shock waves, allowing ongoing nuclear interactions with the solar atmosphere. This extended particle acceleration and interaction phase contrasts with the brief bursts of lower-energy radiation and explains why gamma-ray emission can persist long after the flare’s initial explosion.