Astronomers have uncovered that the Sun is undergoing subtle transformations in ways previously not fully understood, according to groundbreaking new research. By analysing over four decades of solar data, scientists have detected small but significant variations in the Sun's internal structure between its 11-year cycles. These findings could revolutionise our understanding of space weather, which poses potentially catastrophic risks to human civilisation.
Unveiling the Sun's Internal Dynamics
Every 11 years, the Sun transitions from a highly active maximum phase, characterised by numerous sunspots and strong magnetic fields, to a quieter minimum phase with a more uniform surface. However, the latest study reveals that these quiet periods are not identical; each solar minimum exhibits slight behavioural differences. Even minor variations in solar activity lead to important internal changes, challenging previous assumptions about the Sun's consistency.
Analysing Solar Vibrations and Glitches
Researchers focused on tiny vibrations within the Sun, generated by trapped sound waves, to probe its internal conditions. They specifically investigated a "glitch" in these sound waves caused by the double ionisation of helium inside the Sun, alongside changes in sound speed. By examining four distinct solar cycles, the team identified that during the quietest minimum—occurring between 2008 and 2009, spanning cycles 23 and 24—the Sun's internal environment was markedly different.
In this period, the helium glitch was more pronounced, sound speed was higher, and magnetic fields were lower compared to the other three cycles studied. Bill Chaplin from the University of Birmingham emphasised, "For the first time, we've been able to clearly quantify how the Sun's internal structure shifts from one cycle minimum to the next. The Sun's outer layers subtly change across activity cycles, and we found that deep quiet minima can leave a measurable internal fingerprint."
Implications for Space Weather Prediction
This discovery holds profound implications for understanding solar weather, which can trigger energetic outbursts with devastating effects on Earth. Such events may lead to power grid failures, communication system disruptions, and satellite damage. Sarbani Basu from Yale University noted, "Revealing how the Sun behaves beneath its surface during these quiet periods is significant because this behaviour has a strong bearing on how the activity levels build up in the cycles that follow."
The research, detailed in a new paper titled 'The seismic diversity of four successive solar cycle minima as observed by the Birmingham Solar-Oscillations Network (BiSON)', published in the Monthly Notices of the Royal Astronomical Society, aims to enhance predictive models for solar activity. By better grasping these internal shifts, scientists hope to mitigate the risks associated with space weather, safeguarding critical infrastructure and advancing our knowledge of stellar processes.
