There are some changes astronomers noticed while observing Polaris.
When you gaze into the night sky, spotting the North Star, Polaris, isn’t just a moment of wonder. It’s an encounter with the brightest star of the Ursa Minor constellation and a pivotal tool for navigation due to its proximity to the north celestial pole.
Historically, Polaris was understood as a binary system with two significant stars – the F-type yellow supergiant, Polaris Aa, and the smaller main-sequence yellow dwarf, Polaris B. The unique aspect of Polaris Aa is its Cepheid variable nature, where it pulses in a predictable pattern.
Understanding Cepheid Variables
Cepheid variables have the unique trait of radial pulsation, changing in both diameter and temperature. This fluctuation in brightness is crucial for astronomers to measure distances both within and beyond our galaxy.
Polaris was classified as a variable by Danish astronomer Ejnar Hertzsprung in 1911, the same visionary behind the Hertzsprung–Russell diagram. Throughout the last century, data showed a steady pulsation period for Polaris, approximately four days long, and this period lengthened with each passing year.
A Change in the Stars
But this consistent behavior underwent a change. Guillermo Torres of the Harvard & Smithsonian Center for Astrophysics dived into this mystery, revealing in a conversation with Universe Today that the previously lengthening pulsation period has surprisingly begun to decrease after 2010. Such unexpected shifts in behavior signal that the universe still harbors secrets about stars like Polaris.
To further understand this anomaly, Torres delved deep into historical radial velocity (RV) measurements dating back to 1888. RV measurements detect a star’s motion, gauging its velocity by noting shifts in the spectrum. Comprising over 3,600 RV measurements, including those by the Lick Observatory spanning over six decades, Torres pieced together Polaris’ pulsation properties over time.
Revelations and Theories
Contrary to earlier assumptions in the 1990s that Polaris’s pulsations would eventually halt due to dwindling amplitude, the star defied expectations. By the late 1990s, the pulsation amplitude resumed its increase, only to plateau around 2015. Intriguingly, this change seems linked to Polaris’s stellar companion, which orbits close to it every three decades, potentially influencing the pulsations.
Torres believes that this close proximity between Polaris and its partner might be the catalyst for the changes in pulsation. Factoring in this influence, Torres has proposed a refined spectroscopic orbit for the duo, a challenge that has perplexed astronomers for ages.
Unveiling Stellar Secrets
Torres concluded with the assertion that Polaris’s unpredictable nature if confirmed to be a result of its nearby companion’s influence, could provide insights into other pulsating stars. The North Star continues to be a subject of fascination and might still spring more cosmic surprises.
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