Our understanding of how the Sun works remains limited, particularly because directly studying such a massive and hot star is extremely complex. Astronomers must therefore resort to indirect methods, in particular the analysis of sound waves which propagate in depth from the interior of the body.
By compiling forty years of data from helioseismology – a discipline which studies these internal oscillations of the Sun – researchers have highlighted a hitherto unknown phenomenon. They discovered a concentration of solar magnetic activity in a thin layer just below its surface, an observation that sheds new light on the internal workings of the Sun.
The results, published in the journal Monthly Notices of the Royal Astronomical Society and relayed by Gizmodo, reveal the existence of an internal solar biorhythm. This rhythm reflects variations in activity that cannot be detected by traditional observation methods, based mainly on the study of the surface.
According to Sarbani Basu, an astronomer at Yale University (Connecticut) and co-author of the study, the link between the Sun’s internal oscillations and its surface activity has evolved over recent solar cycles. This evolution cannot be explained simply by a weakening of magnetic fields, suggesting deeper changes in the internal structure of the star.
Solar cycles, which last around eleven years, indeed show recent anomalies. Cycle 24, which took place between 2008 and 2019, was significantly weaker than previous ones. As for cycle 25, currently underway, it was initially announced as below average, but ultimately exceeded expectations in terms of sunspot number and radio activity.
A well-hidden scheme
The analysis of so-called “P-mode” oscillations, sound waves whose frequency varies depending on magnetic activity, has made it possible to partly fill this gap. By studying these data over several solar cycles – from cycle 22 to cycle 25, covering the period from 1987 to 2025 – the researchers identified an unprecedented pattern in the internal behavior of the Sun.
This work revealed a gradual transformation of activity below the solar surface over several decades, indicating that the Sun is going through a long-term change in its internal dynamics, at a depth of about 1,000 kilometers. The phenomenon seems particularly marked during the current solar cycle, the intensity of which had been underestimated by classical methods.
However, scientists remain cautious about interpreting these results. They will continue their observations until the end of solar cycle 25, expected around 2030. If this internal biorhythm is confirmed during the next cycle, it could profoundly transform our understanding of the functioning of the Sun and improve the prediction of phenomena linked to space weather.
