Scientists at Skoltech have discovered how the dark regions of the Sun are restored.

The research results have been published in the journal Astronomy&Astrophysics. Coronal mass ejections are massive magnetic bubbles of plasma weighing several billion tons that erupt from the Sun's surface and reach Earth within a few days. This leads to powerful geomagnetic storms capable of disrupting modern technologies that we rely on daily, ultimately affecting our everyday lives.

In May 2024, due to an intense magnetic storm, the routes of transpolar flights had to be altered, and satellites were forced to perform over five thousand maneuvers to avoid drifting off their orbits. Detecting a coronal mass ejection at its initial stage is extremely challenging; such phenomena can only be observed once they have fully formed and come into the view of coronagraphs—devices that simulate a total solar eclipse.

However, we can track signs of ejections directly on the Sun by observing coronal dimmings—dark regions in images of the solar corona in extreme ultraviolet light. Dimmmings reflect the loss of material in the corona during a plasma ejection and serve as a valuable source of information regarding the mass, speed, and direction of its movement. Scientists have developed methods to analyze the lifetime of coronal dimmings, which allow them to determine how and when the solar corona recovers after an ejection. This method is based on long-term observations of coronal dimmings over several days from the onset of the ejection, utilizing satellite data collected from various points in the heliosphere.

“In high-resolution images from the SDO and STEREO spacecraft, we see how coronal loops expand and brighten above the dimming areas following a coronal mass ejection. These loops, which appear both before and after ejections, gradually cover and fill the darkened regions, revealing the mechanism through which the Sun recovers after an ejection,” says the lead author of the study, Julia Ronka, a graduate of the Polytechnic University of Milan, who participated in a student exchange program at Skoltech.

“The characteristic signs of phenomena related to increased solar activity should not be studied in isolation,” notes co-author Galina Chikunova, a graduate of Skoltech’s graduate program who is currently continuing her research at the Hvar Observatory of the University of Zagreb. “By extracting as much information as possible from solar images obtained from various satellites, unexpected correlations can be identified. For instance, we observed that dimmings—traces of solar ejections—often disappear faster than expected. By studying both the dark and bright areas of the solar corona, we discovered a continuous development of coronal loops—an important recovery mechanism—which helps explain why dimmings vanish sooner than anticipated.”

“Coronal loops form in active solar regions. Their formation and dispersion occur constantly, as they expand into the upper layers of the solar corona. Due to their brightness being lower than that of the surrounding structures, detecting them can be difficult; however, their expansion plays a crucial role in accelerating the recovery of dimmings,” adds co-author Tatiana Podladchikova, Director of the System Design Center at Skoltech.

This research opens new horizons in the study of eruptive solar phenomena, providing valuable data on the complex processes underlying the Sun's behavior and its turbulent temperament. The study is supported by a grant from the Russian Science Foundation.