The same nearby star produced six gigantic X-ray flares in just a few months, some lasting up to three days.
The star in question, Sigma Geminorum, belongs to a binary system located in our galactic neighborhood. Two stars orbit each other there. This type of system can exhibit very strong magnetic activity, far greater than what we usually observe on the Sun.
The Chinese Einstein Probe space observatory
Image Wikimedia
The researchers used Einstein Probe, a Chinese space observatory launched in 2024. Its wide-field telescope monitors vast portions of the sky in X-rays. This capability makes it possible to detect phenomena that appear suddenly without having to point the instrument at a specific target in advance.
Between October 2024 and April 2025, the instrument recorded six distinct flares from Sigma Geminorum. They lasted from 21 hours to three days. The researchers classify them as “superflares,” stellar flares that release a very large amount of energy.
To understand this phenomenon, magnetic fields on a star can be viewed as structures capable of accumulating energy. When they suddenly reorganize, this energy is released and strongly heats the surrounding gas. The gas can then emit intensely in the X-ray range.
The six events did not all have the same power. Their total X-ray energy ranged from approximately 1.1 × 1036 to 4.4 × 1037 ergs. Beyond the numbers, their duration and recurrence mainly make it possible to measure the frequency and diversity of this star’s activity.
The Sun also experiences flares linked to its magnetic field. However, Sigma Geminorum belongs to a particularly active category of stars known as RS Canum Venaticorum systems. The proximity of the two stars and their rotation promote intense magnetic activity.
This series of observations also serves as a test for Einstein Probe. The researchers developed a method for automatically extracting changes in brightness and identifying significant flares in the telescope’s long observations.
The method must now be applied to all the stars recorded by Einstein Probe. As observations accumulate, astronomers will be able to compile a large sample of X-ray flares and compare their frequency across different types of stars.