Coronal mass ejections (CMEs) are massive bursts of solar plasma and magnetic fields ejected from the Sun’s corona into space. These eruptions can release billions of tons of charged particles traveling at millions of kilometers per hour. While CMEs are primarily known for their impact on space weather—causing geomagnetic storms, auroras, and disruptions to satellites and power grids—they are also connected to various forms of electromagnetic radiation, including X-rays and gamma rays. But do CMEs themselves produce gamma rays directly? The answer involves understanding the complex processes occurring during solar eruptions and the relationship between CMEs, solar flares, and high-energy radiation.
Solar flares and CMEs often occur together but are distinct phenomena. Solar flares are intense bursts of radiation caused by the sudden release of magnetic energy stored in the Sun’s atmosphere. These flares emit a broad spectrum of electromagnetic radiation, including visible light, ultraviolet, X-rays, and gamma rays. Gamma rays from solar flares are produced when accelerated particles, such as electrons and protons, collide with the solar atmosphere, generating high-energy photons. This process is well documented and is a primary source of solar gamma-ray emission.
CMEs, on the other hand, are large-scale expulsions of plasma and magnetic fields that travel outward from the Sun. They are often associated with shock waves that accelerate particles to very high energies as they move through the solar corona and interplanetary space. These accelerated particles, known as solar energetic particles (SEPs), can reach Earth and other planets, posing radiation hazards to astronauts and spacecraft. The acceleration of particles by CME-driven shocks is a key mechanism for producing energetic protons and heavier ions.
While CMEs themselves do not directly emit gamma rays in the same way solar flares do, the shock waves they generate can accelerate particles to energies high enough to produce gamma rays indirectly. When these accelerated particles interact with the solar atmosphere or with interplanetary material, they can produce gamma-ray emission through processes such as nuclear interactions and bremsstrahlung radiation. This means that gamma rays observed during solar events can sometimes be linked to CME-driven shocks, especially during large, gradual solar energetic particle events.
Observations from space missions equipped with particle detectors and telescopes have shown that many solar energetic particle events are associated with CMEs. These events often display a gradual increase in particle intensity, consistent with acceleration by CME shocks rather than the impulsive bursts linked to solar flares. The gamma rays produced in these contexts tend to be less intense and have different temporal profiles compared to flare-associated gamma rays.
In addition, some studies have detected gamma-ray emission from the Sun that lasts much longer than the typical duration of a solar flare, suggesting a connection to CME-driven particle acceleration. This extended gamma-ray emission may arise from particles trapped in magnetic fields near the Sun or from ongoing interactions as the CME propagates outward.
In summary, while coronal mass ejections do not produce gamma rays directly as a primary emission like solar flares, they play a significant role in accelerating particles that can generate gamma rays through secondary interactions. The gamma rays associated with CMEs are generally linked to the energetic particles accelerated by CME-driven shocks and their subsequent collisions with solar or interplanetary material. This interplay between CMEs, particle acceleration, and gamma-ray production is a key area of study in solar and space physics, helping scientists understand the complex dynamics of solar eruptions and their impact on the heliosphere.