Scientists reveal the North Star's secrets through high-resolution images captured for the first time; check for more details.

Polaris and its companion, as observed by the Hubble Space Telescope in 2006.

For the first time, scientists have captured high-resolution images of Polaris, the North Star, uncovering surprising features that challenge long-held assumptions about this celestial icon.

Polaris’s Dynamic Surface
Nestled high in the skies, Polaris has been a steadfast guide for travellers and astronomers alike, its position in the night sky seemingly constant. Yet, recent images from the CHARA Array at Mount Wilson, California, have revealed that Polaris is far more dynamic than previously thought. Using a network of telescopes that work together to create a single, high-resolution lens, astronomers have resolved unprecedented details on Polaris’s surface.

These images reveal large spots, both bright and dark, on the star’s surface. These spots are similar to the sunspots observed on our Sun. Unlike previous depictions of Polaris as a smooth, consistent star, these spots indicate a much more complex and active surface. According to Gail Schaefer, director of the CHARA Array, “The CHARA images revealed large bright and dark spots on the surface of Polaris that changed over time.” This discovery suggests that the star’s magnetic activity could be influencing its luminosity in ways that are not yet fully understood.

A false-colour image of Polaris from the CHARA Array, captured in April 2021, reveals large bright and dark spots on the star's surface. Polaris appears approximately 600,000 times smaller than the full moon in the sky. (Imager: CHARA Array)

Challenging the Understanding of Cepheid Variables
Polaris is not just any star; it is a Cepheid variable, known for its regular pulsations—periodic expansions and contractions of its outer layers that cause predictable changes in brightness. These pulsations have made Cepheids, including Polaris, essential tools for measuring cosmic distances, as their brightness fluctuations serve as reliable indicators of their true luminosity.

However, the newly discovered surface spots on Polaris introduce an additional factor into the equation. Traditionally, the star’s brightness was thought to be governed solely by its pulsation cycles. The discovery of these spots suggests that magnetic activity might also play a role, potentially affecting the star’s luminosity and challenging existing models of Cepheid variable behaviour.

Polaris and its companion, as observed by the Hubble Space Telescope in 2006. (Image: NASA/ESA)

Revisiting Polaris’s Mass and Complexity
The study also shed new light on Polaris’s mass and structure. While previous estimates suggested that Polaris was several times the mass of the Sun, recent observations indicate that it could be up to five times more massive. This finding has significant implications for our understanding of Cepheid stars, as it suggests that Polaris is more luminous than previously believed.

Adding to the complexity, Polaris is part of a triple-star system, with a binary companion that orbits every 30 years. This close orbit, combined with the vast difference in brightness between the two stars, makes it challenging for astronomers to study the system in detail. “The small separation and large contrast in brightness between the two stars makes it extremely challenging to resolve the binary system during their closest approach,” noted Nancy Evans, an astronomer at the Center for Astrophysics, Harvard & Smithsonian.

The discovery of Polaris’s increased mass raises new questions for scientists, suggesting that current models of Cepheid variables might need to be revisited. Understanding these stars better could have broader implications for our knowledge of stellar evolution.

Looking Ahead: Future Research
The discovery of surface spots on Polaris, coupled with the new insights into its mass and complexity, opens up exciting avenues for future research. Scientists are eager to continue observing Polaris to better understand the nature of these spots and their impact on the star’s behaviour.

“We plan to continue imaging Polaris in the future to better understand the mechanism that generates the spots on its surface,” said John Monnier, an astronomy professor at the University of Michigan. These future studies could provide critical insights into the role of magnetic fields in the behaviour of Cepheid variables and offer a deeper understanding of the life cycles of stars.

By studying stars like Polaris, which serve as cosmic distance markers, astronomers hope to refine their techniques for measuring the universe’s scale. These discoveries may not only enhance our understanding of Cepheid stars but also pave the way for new breakthroughs in the field of astronomy.