Astronomers are investigating the sound waves that travel within the Sun. This method, referred to as asteroseismology or helioseismology, offers a glimpse into the Sun’s internal structure. Evidence gathered over four decades suggests that transformations are occurring in the Sun’s core. The findings from a recent study have been published in the Monthly Notices of the Royal Astronomical Society.
The Sun undergoes an 11-year cycle of activity, from one minimum to the next. We have recently passed the peak of the 25th cycle, but the new research indicates that since the 23rd cycle, the relationship between oscillation frequencies and conventional activity indicators has shifted.
The 24th cycle proved unexpectedly weaker across all metrics. While the 25th cycle appears weaker based on surface indicators, it has actually been exceptionally strong and active. Seismic data supports this observation.
Low, medium, and high-frequency oscillations seem to point to internal structural changes within the Sun. Solar magnetic activity, which is how the cycle manifests, is becoming concentrated in an increasingly thinner layer just beneath the photosphere, the Sun’s visible surface.
Data collected between 1987 and 2025 by six telescopes from the Birmingham Solar Oscillations Network (BiSON) showcases these long-term variations in solar activity.
“The Sun has its own ‘active biorhythm’ that generates the rises and falls in magnetic activity shaping space weather. However, traditional surface measurements don’t tell the whole story – it’s possible the Sun is entering a different mode of behavior that will play out over decades,” explains lead author Professor Bill Chaplin from the University of Birmingham. “We found evidence of systematic changes in the solar activity cycle. Crucially, magnetic activity is becoming more localized near the surface with each cycle. This is the first time this has been discovered, and it wouldn’t have been possible without long-term observations from the BiSON telescope.”
Solar activity impacts our planet and the surrounding space weather. A powerful solar cycle can lead to numerous geomagnetic storms. Understanding the factors that govern the Sun’s behavior is paramount for accurate predictions.
“We have found that the relationship between internal solar oscillations and surface activity has been changing over the last few cycles,” state the study authors. “This trend cannot be explained simply by weakening magnetic fields. Instead, it suggests a structural reorganization in how the Sun stores magnetic activity beneath its surface.”
Is this a long-term shift in solar activity, or will our star revert to its previous state within the next few years? The team will continue to utilize the BiSON telescope throughout the remainder of the 25th cycle and into the 26th cycle, expected to begin around 2030, to determine the answer.
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