Indian scientists decode 30 years of solar data to solve Sun's bright poles mystery

A multi-institutional team of Indian astronomers has solved a decades-old solar mystery, deciphering why the Sun’s polar regions emit intense brightness when mapped at microwave frequencies.

The breakthrough, announced by the Ministry of Science and Technology on 12 October, draws on nearly 30 years of continuous solar data. By unravelling the mechanisms behind what astrophysicists call microwave polar brightening, the study provides fresh insight into the magnetic activity and temperature structures governing the Sun’s polar crown.

Understanding these polar regions is crucial for life and technology on Earth. The Sun's poles drive the solar wind and shape interplanetary magnetic fields. When major solar disruptions occur, they generate geomagnetic storms that can disrupt power grids, knock out satellite operations, and scramble high-frequency radio communications.

Decades of observations unpicked

While microwave brightening near the poles has been observed for decades, its precise causes had remained a point of debate. Researchers knew polar coronal holes, magnetic concentrations, and bright atmospheric patches played some role, but the exact balance between them was unknown.

To resolve the question, the Indian research group pulled together three decades of observations from the Nobeyama Radioheliograph, a specialised solar radio telescope in Japan. They paired this long-term radio record with extreme-ultraviolet data from NASA’s space-based Solar Dynamics Observatory and surface magnetic measurements collected by the Wilcox Solar Observatory in California.

The extensive study involved astronomers and physicists from the Aryabhatta Research Institute of Observational Sciences in Nainital, the Udaipur Solar Observatory, Mahatma Jyotiba Phule Rohilkhand University in Bareilly, and three Indian Institutes of Technology: IIT Delhi, IIT Gandhinagar, and IIT Roorkee.

Magnetic forces at the poles

The findings, published in The Astrophysical Journal, reveal a distinct north–south asymmetry in how microwave brightening evolves over time alongside polar coronal holes—dark, open-field areas where high-speed solar wind streams escape into space.

The team demonstrated that while microwave brightening tracks the expanding and contracting surface area of coronal holes, it correlates even more powerfully with the actual strength of the Sun’s polar magnetic field.

When the scientists zoomed in on individual bright patches using simultaneous ultraviolet imaging, they found that many coincided with compact features known as coronal bright points. These bright spots are powered by miniature magnetic loops nested within the broader polar holes. In several instances, the patches aligned with energetic coronal jets, showing that the Sun's polar atmosphere is agitated by continuous small-scale magnetic reconnection alongside its grand solar cycles.

According to the Ministry of Science and Technology, the research delivers definitive observational evidence that both large-scale magnetic structures and local magnetic activity govern polar microwave emissions. The milestone reflects India's growing leadership in solar physics, providing tools that will enhance space weather models and safeguard orbital infrastructure.