Study of 138 stars shows the Sun’s magnetic cycle is not unique

Earth experiences seasons because of its axial tilt. The Sun, however, has its own version of seasons driven by magnetic activity. Every 11 years, the Sun’s magnetic poles flip — north becomes south, and south becomes north. This reversal marks a full solar cycle.

At the peak of the cycle, known as solar maximum, sunspots and solar flares are common events, releasing streams of charged particles that interact with Earth’s magnetic field and produce auroras near the poles. They can also interfere with satellites, disrupt radio communications, and stress electrical grids.

The most extreme example is the Carrington Event of 1859, which caused telegraph failures worldwide and produced auroras as far south as the Caribbean. More recently, in March 1989, a powerful geomagnetic storm caused a blackout in Quebec, Canada, affecting millions of people for hours.

What the new study found

An international team led by Dr. Deepak Chahal of Macquarie University set out to test whether the Sun’s magnetic behaviour is typical or unusual. The group analyzed 14 years of combined photometric observations from three major surveys: the Kepler Full Frame Images (FFIs), the All-Sky Automated Survey for Supernovae (ASAS-SN), and the Zwicky Transient Facility (ZTF).

The dataset covered:

• 70 stars observed with Kepler–ASAS-SN–ZTF,
• 68 stars observed with Kepler–ZTF, and
• 25 RS CVn candidates (close binary systems with strong magnetic activity).

In total, 138 G–K-type main-sequence stars were examined. These are stars similar in mass and temperature to the Sun but often younger and rotating faster.

The team tracked brightness variations caused by starspots and faculae, stellar equivalents of sunspots and bright magnetic regions, to infer magnetic cycles.

Patterns of magnetic activity

The study found that fast-rotating G–K-type stars do not follow the expected correlation between rotation period and cycle length. Instead, many stars fell into an intermediate region of the activity–rotation diagram, the same area where the Sun is located.

• 34% of stars in the sample were in this intermediate region.
• 23% of young Sun-like stars also appeared here.

This challenges the long-standing model that stars follow either an “active” or “inactive” magnetic branch. The Sun, once thought to be an outlier, appears instead to be part of a common evolutionary pattern.

“We found several young Sun-like stars with magnetic cycles similar to our Sun, but shorter,” said Dr. Chahal. “As these stars age and slow down, their cycles may evolve into patterns resembling our Sun’s current 11-year cycle.”

Why it matters for Earth

Solar storms are not just astronomical curiosities. They directly affect modern technology. Coronal mass ejections can disable satellites, interfere with GPS navigation, and pose hazards to astronauts, while radiation storms can expose airline passengers on polar routes to elevated doses.

“If a solar storm the size of the Carrington Event occurred today, it could disrupt GPS, banking, aviation, and communications systems, potentially causing trillions of dollars in damage,” said Associate Professor Devika Kamath, co-author of the study.

The new findings suggest the Sun is not unique in its behaviour. Understanding where our star fits into the wider stellar population provides a foundation for better forecasting. By learning how magnetic cycles change with age, scientists can anticipate future phases of the Sun’s activity and improve space weather models.

Looking beyond our Sun

“Understanding the patterns of stellar activity cycles helps us better predict when dangerous space weather events might occur, not just around our own Sun but potentially around other stars with planetary systems,” said Professor Richard de Grijs, co-author of the study.

For exoplanets orbiting young, active stars, strong magnetic cycles could mean harsher radiation environments — a factor influencing habitability.

For Earth, the research serves as a reminder that living with an active star comes with recurring risks that require constant monitoring and preparedness.

Dynamo theory and stellar evolution

The underlying process driving stellar cycles is the stellar dynamo. It arises from the interplay of plasma flows inside stars: differential rotation, convection, and magnetic feedback. The cycle gradually flips the star’s magnetic field, producing the periodic activity observed at the surface.

Previous studies proposed distinct dynamo regimes, but the intermediate group identified in this study shows that stellar dynamos may operate across a broader continuum. The Sun’s position in this group suggests that its 11-year cycle is a representative — not exceptional — case of stellar magnetic behaviour.

References:

¹ Please explain: Does the sun have seasons? – Macquarie University – September 10, 2025

² Photometric activity cycles in fast-rotating stars: revisiting the reality of stellar activity cycle branches – Deepak Chahal et al. – Monthly Notices of the Royal Astronomical Society – May 8, 2025 – https://doi.org/10.1093/mnras/staf754 – OPEN ACCESS

Reet Kaur

I’m a science journalist and researcher at The Watchers, contributing to the Epicenter edition, where I cover peer-reviewed scientific research and emerging discoveries across Earth and space sciences. With a background in astronomy and a passion for environmental science, I’ve worked in shark and coral conservation in Fiji, conducting reef and shark-behavior research, contributing to mangrove restoration, and earning PADI Open Water and Coral Reef Certifications. I bring a blend of scientific rigor and storytelling to illuminate the discoveries shaping our planet and beyond.

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