An international team of astronomers using the Solar Orbiter spacecraft has uncovered how powerful solar flares are born. It turns out they do not begin with a single explosive event, but with a chain of weak magnetic disturbances that rapidly intensify and grow into an avalanche-like process. The results were published in the journal Astronomy and Astrophysics.

Rare Observations from Close Range

Solar Orbiter, a mission of the European Space Agency, approached the Sun at a record-close distance. At that moment, the probe captured one of the most detailed solar flares ever observed. Scientists were able to track events almost forty minutes before the peak and see how magnetic structures gradually accumulated and unraveled in the solar corona.

At first, a system of thin, intertwined magnetic threads appears in the Sun’s atmosphere, holding extremely hot plasma. These structures are unstable. Individual parts of the magnetic field break and immediately reconnect. Each act of magnetic reconnection releases energy that triggers the next one. As a result, the process becomes avalanche-like, with weak events rapidly escalating into a powerful flare.

Plasma Rain and Relativistic Particles

Particular attention was drawn to a phenomenon the authors called plasma rain. Even before the main phase of the flare and for some time after it, streams of hot clumps of plasma rush downward through the Sun’s atmosphere. These flows are a sign of active energy transfer from the magnetic field to matter.

X-ray observations showed that particles are accelerated to speeds of forty to fifty percent of the speed of light. This makes such flares potentially dangerous for spacecraft and astronauts.

Previously, the avalanche model was considered only as a statistical explanation for the large number of flares observed on the Sun and other stars. Now, for the first time, it has been shown that even a single large flare can be the result of a cascade of many small events.

Importance for Space Weather Forecasting

This discovery changes our understanding of how energy is released on the Sun. Knowing how small magnetic disturbances grow into colossal energy outbursts will help improve forecasts of space weather, including solar flares, coronal mass ejections, and geomagnetic storms that affect satellites, power grids, and radio communications.

The authors emphasize that these data are among the most important obtained during the entire Solar Orbiter mission. In the future, scientists hope to confirm that this avalanche mechanism is universal and operates not only on the Sun but also on other active stars.

In Brief

Using the Solar Orbiter probe, astronomers have shown for the first time that powerful solar flares begin like an avalanche: a chain of weak magnetic reconnections rapidly intensifies and grows into a giant release of energy. Before and after the flare’s peak, plasma rain is observed, streams of plasma containing particles moving at up to fifty percent of the speed of light. This discovery changes our understanding of how flares work and will improve space weather forecasts. It is one of the most significant results of the Solar Orbiter mission.