The Sun is experiencing long-term changes, as revealed by an international team of researchers led by the University of Birmingham, who have identified a major squeeze in the four most recent solar activity cycles.
A recent paper in the Monthly Notices of the Royal Astronomical Society by the University of Birmingham-led team reveals that Solar magnetic activity is now being forced into a shallow layer of the Sun, just beneath the solar surface, marking a major change to our host star’s active biorhythm.
The Sun’s 11-year cycles of activity range from a low ebb to robust periods, producing explosive events such as highly charged particle ejections and coronal mass ejections, which are major drivers of dangerous space weather.
Inside the Sun
Below the solar surface, processes generate the Sun’s magnetic field, which drives the solar cycles, which in turn drive space weather. Space weather can be extremely hazardous to the electronic and communications infrastructure we rely on, both in space and on Earth’s surface, including GPS systems and the power grid. Therefore, as our reliance on that infrastructure grows, accurately predicting space weather has become an increasingly important concern.
Scientists have primarily used external markers, such as sunspots, to track solar activity, but, like in any system, much of what drives the Sun occurs beneath the surface. To pierce the solar veil, the researchers have adopted a technique called helioseismology, which allows them to listen to small sound waves from inside the Sun. These waves reveal minute changes beneath the surface, providing a very different understanding of the most recent solar cycles than what could be observed from external markers.
A History of the Sun
The research relied on nearly four decades of helioseismic data collected by the Birmingham Solar Oscillations Network (BiSON) of six telescopes located around the globe. Finally, researchers had sufficient historical data on the Sun’s inner workings to conduct a lengthy study of how these workings have changed over time.
In their analysis of that data, the international team identified a slow but growing change in the structure of the Sun’s interior, occurring across multiple cycles.
“The Sun has its own ‘active biorhythm’ creating rising and falling magnetic activity that shapes space weather,” said lead author Professor Bill Chaplin, from the University of Birmingham. “However, traditional surface measures don’t capture the full story – that the Sun may be entering a different mode of behavior unfolding over decades.”
“We have uncovered evidence of systematic changes in the solar activity cycle,” Chaplin added. “Crucially, magnetic activity is becoming more tightly confined near the surface with each cycle. This is the first such discovery and would have been impossible without the long BiSON observations.”
A Deeper Look
From 1987 through 2025, during cycles 22-25, shifts in p-mode oscillations driven by magnetic activity revealed internal changes in the Sun. The team identified three different groups of oscillations, marked by the low, medium, and high-frequency bands, each penetrating the solar surface to a different depth. Compared with traditional external markers, the data revealed three unique elements.
Since cycle 23, oscillation frequencies and external markers have begun telling very different stories, indicating major changes in the Sun’s internal workings. As time goes on, more and more of the changes are occurring near the surface, at depths of less than 1,000 kilometers. In the most recent cycle, 25, helioseismic data are giving off much stronger indications of this activity than surface markers.
According to the researchers, weakening magnetic fields cannot account for the changes observed, suggesting a major structural reorganization beneath the Sun’s surface.
The team says that continuing exploitation of the BiSON data into cycle 26 will be essential to determining whether this indicates a sustained change in solar activity.
The paper, “Sub-Surface Structural Changes Associated with Successive 11-yr Solar Activity Cycles Have Been Progressively More Confined Near the Surface: New Helioseismic Results on Cycles 22– 25 from BiSON,” appeared in Monthly Notices of the Royal Astronomical Society on May 28, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.