For many years, the activity of the Sun's 11-year solar cycle has been measured through visible indicators such as sunspots, solar activity, magnetic fields, and radio waves. However, recent findings from the Birmingham Solar-Oscillations Network (BiSON) suggest that there may be an underlying solar signal forming deep within the Sun. Scientists have observed that structural changes related to Solar Cycles 22, 23, 24, and 25 are moving progressively deeper toward the outer layers of the solar core. This discovery has significant implications for how solar activity has traditionally been monitored and what other scientific fields can learn from this phenomenon.
Solar Cycle Study Uncovers a Hidden Signal Beneath the Sun
A team led by Professor William J. Chaplin from the University of Birmingham analyzed nearly four decades of helioseismic observations collected by BiSON, a global network that measures oscillations inside the Sun. Unlike traditional methods that track surface activity through sunspots and radio flux, helioseismology studies acoustic waves, specifically p-mode acoustic waves, which are sound waves traveling through the Sun's interior. These waves help scientists investigate structures below the Sun's surface.
According to the study, the relationship between surface solar activity and seismic activity beneath it has changed significantly during Solar Cycle 25. The researchers stated, "Cycle 25 is as strong as Cycles 22 and 23 when studied in this high-frequency seismic band, unlike the relative sizes of the cycles in the activity proxies." Overall, the findings indicate that solar activity inside the Sun is much higher than what is observed at the surface.
Study Reveals Changes Closer to the Solar Surface
It was revealed that structural processes within the Sun have been moving nearer to the surface with each solar cycle. In older cycles, these processes were much deeper, but recent research shows that structural changes are now limited to a narrow layer close to the star's surface. Higher-frequency modes are more responsive to structural processes occurring within about 1,000 kilometers of the surface. The study discovered an unusually high number of these processes in the upper layers of the Sun during Solar Cycle 25.
The researchers concluded that "subsurface structural changes occurring in successive 11-year cycles are increasingly progressively confined near the surface." This phenomenon is believed to have started during the declining phase of Solar Cycle 23 and persisted through Cycles 24 and 25. Moreover, these results confirm earlier BiSON research from 2017, which suggested that the Sun may be undergoing significant changes related to its dynamo. That study noted that "a fundamental change in the nature of the solar dynamo may be in progress."
What the Hidden Solar Signal Could Mean for Future Solar Activity
The cause of this change remains unknown. The study shows that changing magnetic field strength alone cannot explain the observed phenomenon. However, it appears that magnetic structures are becoming increasingly compacted within shallower depths beneath the solar surface. This is significant because the solar dynamo generates solar flares, coronal mass ejections, and other space weather phenomena that can affect satellites, terrestrial communications, and energy networks.
The latest results align with other recent research on long-term changes in sunspot behavior and subsurface layers. Studies in recent years have established changes in sunspot strength, oscillations of the solar seismic radius, and other anomalies in the magnetic environment, indicating that a different phase of the Sun's life cycle may be beginning. While the researchers emphasize that further investigation is needed, their conclusions are intriguing: some major processes occurring in the Sun may no longer be understood solely from surface observations.
For now, the hidden signal detected through helioseismology offers a rare glimpse beneath the Sun's outer layers and suggests that there is still much to learn about the star that sustains life on Earth.
