scientists have tracked the Sun by observing its surface activity—counting sunspots, monitoring solar flares, and measuring bursts of radiation. But new research suggests that what we see on the surface may not tell the whole story.
By effectively "listening" to vibrations deep inside the Sun, astronomers have discovered significant changes occurring beneath its surface over the past 40 years. Their findings hint that our star may be entering a new phase of behavior.
"We have uncovered evidence of systematic changes in the solar activity cycle," says astrophysicist Bill Chaplin of the University of Birmingham, who led the study. "Most importantly, magnetic activity appears to be becoming increasingly concentrated near the Sun's surface with each cycle."
The Sun follows a roughly 11-year activity cycle, alternating between quieter and more active periods. During a solar minimum, the Sun is relatively calm. During a solar maximum, however, it becomes far more turbulent, unleashing powerful solar flares and coronal mass ejections that can interfere with satellites, GPS systems, communications networks, and even power grids on Earth.
These cycles are driven by the Sun's magnetic field. Deep inside the star, hot electrically charged plasma is constantly churning. Combined with the Sun's uneven rotation—faster at the equator than at the poles—this movement twists and stretches magnetic field lines in a complex cosmic dance. Eventually, the magnetic poles flip, marking the completion of one solar cycle.
Recent cycles have shown notable differences from those that came before. Solar Cycle 24, for instance, was significantly weaker than previous cycles, producing fewer sunspots and lower levels of radiation. Scientists expected the current Solar Cycle 25 to continue that trend, but new evidence suggests something more complicated is happening beneath the surface.
To investigate, Chaplin and his team analyzed nearly four decades of observations collected by the Birmingham Solar Oscillations Network (BiSON), a global network of six observatories that has continuously monitored the Sun since the 1970s.
BiSON uses a technique called helioseismology, which studies tiny vibrations within the Sun. Much like earthquakes reveal the interior of Earth, these vibrations allow scientists to probe the Sun's hidden layers. Sound waves travel through the star, causing it to "ring" like a giant thermonuclear bell.
The researchers examined different vibration frequencies to study activity at various depths inside the Sun. They then compared those findings with traditional measures of solar activity, such as sunspot numbers and radio emissions from the Sun's atmosphere.
What they found was surprising.
While surface activity appears weaker than expected, deeper measurements tell a different story. High-frequency oscillations within the Sun remain relatively strong, resembling levels seen during older, more active solar cycles.
This suggests that the magnetic and structural changes driving the solar cycle are becoming concentrated in a much shallower region—roughly 1,000 kilometers beneath the Sun's surface.
According to the researchers, this is the first time such a pattern has been observed, and it was only possible because of BiSON's exceptionally long observational record.
The discovery could have practical consequences as well. A better understanding of how magnetic fields behave inside the Sun could improve space-weather forecasting, helping scientists predict solar storms that can affect Earth's technological infrastructure.
The findings also reveal that the relationship between the Sun's interior and its visible surface is evolving.
"We discovered that the relationship between internal solar oscillations and surface activity has changed over the past few cycles," says astronomer Sarbani Basu of Yale University.
Scientists will continue monitoring the Sun as Solar Cycle 25 winds down and Solar Cycle 26 approaches around 2030. The big question now is whether this newly observed trend will continue or whether the Sun will once again surprise us.
Either way, the evidence points to something significant happening beneath the solar surface.
"This trend cannot be explained simply by weaker magnetic fields," Basu says. "Instead, it suggests a structural reorganization of how the Sun stores magnetic activity beneath its surface."
The study, published in the journal Monthly Notices of the Royal Astronomical Society, offers a rare glimpse into the hidden workings of our closest star—and suggests that the Sun may be changing in ways we are only beginning to understand.
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