Researchers using the Center for High Angular Resolution Astronomy (CHARA) Array at Georgia State University have conducted a study on the North Star, Polaris, which has revealed new details about the star’s size and appearance. Polaris is a triple-star system and a pulsating variable star, meaning that it periodically changes in brightness as its diameter fluctuates over a four-day cycle. This study aimed to map the orbit of a close, faint companion star that orbits Polaris every 30 years.
Polaris is classified as a Cepheid variable star, which means that its true brightness depends on its period of pulsation. Brighter Cepheid stars pulsate slower than fainter ones, making them useful for astronomers as “standard candles.” This allows astronomers to measure the distances to these stars and infer the expansion rate of the universe based on their true brightness. The team of astronomers led by Nancy Evans from the Center for Astrophysics | Harvard & Smithsonian used the CHARA Array to observe Polaris and track the orbit of its companion star, which is challenging due to the small separation and large contrast in brightness between the two stars.
Using six telescopes at the Mount Wilson Observatory in California, the CHARA Array acted as a 330-meter telescope to detect the faint companion as it passed close to Polaris. The observations were recorded using the MIRC-X camera, which has the ability to capture details of stellar surfaces. The team successfully tracked the orbit of the companion star and measured changes in the size of Polaris as it pulsated, revealing that Polaris has a mass five times larger than the Sun and a diameter 46 times that of the Sun.
One of the most surprising findings from the study was the appearance of Polaris in close-up images taken by the CHARA Array. The images revealed large bright and dark spots on the surface of Polaris, which changed over time. This discovery provides the first glimpse of what the surface of a Cepheid variable star looks like and raises questions about the mechanism that generates these spots. The team plans to continue imaging Polaris in the future in order to better understand this phenomenon.
The observations of Polaris were made as part of the open access program at the CHARA Array, where astronomers from around the world can apply for time through the National Optical-Infrared Astronomy Research Laboratory (NOIRLab). The CHARA Array is located at the Mount Wilson Observatory in California, with its six telescopes arranged along three arms that converge on the MIRC-X camera in the central beam combining lab. The open access program is funded by the National Science Foundation and receives institutional support from Georgia State University.
In conclusion, the study of Polaris using the CHARA Array has provided valuable insights into the size, appearance, and behavior of this important star. The observations have shed light on the orbit of its companion star, the mechanism behind the bright and dark spots on its surface, and its role as a Cepheid variable star. This research contributes to our understanding of the universe and showcases the capabilities of the CHARA Array in advancing astronomical knowledge.