Solar Orbiter Sheds Light on Sun’s Fiery Tango: A Surprising Magnetic Twist

The Solar Orbiter has made a groundbreaking discovery: solar flares are initiated by small but rapidly intensifying disturbances, much like an avalanche in the mountains. This process results in a plasma ‘rain’ that continues even after the flare itself has subsided. These findings are based on detailed observations of a major solar flare that occurred on September 30, 2024. Solar flares are powerful explosions on the Sun that happen with the sudden release of energy stored in twisted magnetic fields. This process, known as ‘reconnection,’ occurs within minutes: magnetic field lines of opposite directions break and reconnect. The energy released heats the plasma to millions of degrees and accelerates particles, leading to solar flares. In turn, solar flares can cause geomagnetic storms on Earth, leading to radio communication disruptions and satellite damage. The power of flares is classified using Latin alphabet letters (A, B, C, M, X), with the class X being the most powerful.

High-resolution images obtained by the Solar Orbiter spacecraft allow us to examine the minutest details of the ‘magnetic avalanche’ that led to the significant solar flare on September 30, 2024. Source: ESA & NASA / Solar Orbiter / EUI Team.

Unprecedented Insights

New data from the Solar Orbiter, derived from four instruments, has provided the most comprehensive understanding of a solar flare to date. The EUI (Extreme Ultraviolet Imager) instrument captured high-resolution images in the ultraviolet range, showing details mere hundreds of kilometers in size in the solar corona at a rate of two frames per second. Other instruments-SPICE, STIX, and PHI-analyzed various layers of the solar atmosphere and temperature ranges, from the corona to the photosphere. Observations covered a 40-minute period preceding the flare.

The analysis revealed that 40 minutes before the peak activity of the flare, an arched structure comprising twisted magnetic fields and plasma was already present in the observed region, associated with a cross-like structure of intensifying magnetic force lines. Further scaling up revealed that new magnetic threads appeared in each frame (every two seconds or faster). These threads twisted and led to instability in the region. Twisted threads began breaking and reconnecting, initiating a cascade of further destabilizations. This led to stronger reconnections and energy ejections, which manifested as a sudden brightness increase.

Magnetic Cascade and Particle Acceleration

A particularly strong brightness increase begins in the next phase, followed by the disconnection of a dark thread from one side, its ejection into space, and simultaneous spinning at high speed. Bright reconnection sparks are visible along the entire thread when the main flare occurs.

For the first time, simultaneous measurements by SPICE and STIX instruments allowed the study of how a rapid series of reconnections transfers energy to the outer part of the solar atmosphere. Of particular interest is high-energy X-ray radiation, which indicates where accelerated particles have expended their energy. During the September 30 flare, the X-ray radiation sharply increased, and particles accelerated to 40–50% of light speed (431–540 million km/h).

Observations showed that energy transferred from the magnetic field to the surrounding plasma during reconnections. After the main phase of the flare, the cross-like shape of magnetic force lines disintegrated, and the plasma began cooling, while the radiation of particles decreased to ‘normal’ levels. Simultaneously, the PHI instrument recorded the flare’s imprint on the Sun’s visible surface, completing a three-dimensional picture of the event.