Pulsation of Polaris, the North Star, Shows Unexpected Changes
When gazing at the night sky and locating the North Star, also known as Polaris, one is actually looking at the brightest star in the Ursa Minor constellation, otherwise known as the Little Dipper. Not only is Polaris a significant star in terms of its brightness, but its proximity to the north celestial pole makes it quite useful for orienteering and navigation. However, recent studies have revealed unexpected changes in the pulsation of Polaris, leaving astronomers puzzled and eager to unravel its mysteries.
Polaris is a binary system that consists of two stars: an F-type yellow supergiant named Polaris Aa, and a smaller main-sequence yellow dwarf referred to as Polaris B. These stars are part of a stellar class called Cepheid variables, which pulsate regularly and are known for their radial pulsations causing changes in diameter and temperature. These variations directly affect their brightness, making Cepheid variables valuable tools for calculating galactic and extragalactic distances.
Throughout most of the 20th century, records indicated that the pulsation period of Polaris has been steadily increasing, while the pulsation amplitude has been declining. However, recent observations have shown a dramatic shift in this trend. According to a new study led by Guillermo Torres, an astronomer with the Harvard & Smithsonian Center for Astrophysics (CfA), the pulsation period of Polaris has started getting shorter, and the amplitude of velocity variations has stopped increasing.
Dr. Torres suggests that these unexpected changes in Polaris’ pulsation behavior could be linked to long-term changes related to the binary nature of the system. As the two stars get closer to each other, the secondary star perturbs the atmosphere of the primary star, leading to alterations in its pulsation period and amplitude.
To gain a deeper understanding of these pulsation changes, Dr. Torres examined over 3,600 radial velocity measurements dating back to 1888. These measurements involved analyzing spectra from Polaris and identifying indications of redshift and blueshift, which reveal the star’s back-and-forth motion and velocity.
The analysis revealed a revolutionizing insight into the pulsation properties of Polaris. In the early 1990s, the amplitude of the pulsations had become so small that astronomers believed they were about to cease. However, Polaris surprised them and by the late 1990s, the amplitude started increasing again until around 2015. Recent observations indicate that the amplitude is no longer increasing and may begin to decrease. Furthermore, radial velocity measurements suggest that these changes may be influenced by the presence of another star orbiting Polaris, which comes closer to it every 30 years and may disturb the outer layers where the pulsations occur.
These discoveries provide important insights into the irregular and unpredictable behavior of Polaris. If confirmed that these changes are caused by the presence of its companion star, it could shed light on the behavior of other stars with similar properties and aid in understanding the nature of their oscillations. Dr. Torres emphasized the significance of keeping an eye on Polaris, as it may hold more surprises in the future.
This study is expected to contribute to further research on Cepheid variables and their behavior, improving our understanding of these fascinating stellar objects. As scientists continue to explore the mysteries of the universe, Polaris remains a captivating star that continues to astound astronomers with its pulsating nature.