Polaris is the closest, brightest cepheid variable. Very recently, something changed
When you look up in the night sky and find your way to the North Star, you are looking at Polaris. Not only is it the brightest star in the Ursa Minor constellation (the Little Dipper), but its position relative to the north ...
For most of the 20th century, records indicate that the pulsation period has been increasing while the pulsation amplitude has been declining. But recently, this changed as the pulsation period started getting shorter while the amplitude of the velocity variations stopped increasing. According to a new study published on the arXiv preprint server by Guillermo Torres, an astronomer with the Harvard & Smithsonian Center for Astrophysics (CfA), these behaviors could be attributed to long-term changes related to the binary nature of the system, where the two stars get closer to each other, and the secondary perturbs the atmosphere of the primary.
Cepheid variables are stars that pulsate radially, causing them to vary in diameter and temperature. These pulsations are directly related to changes in their brightness, which makes them a useful tool for measuring galactic and extragalactic distances. The variable nature of Polaris was confirmed in 1911 by Danish astronomer Ejnar HertzsDaprung, for whom the Hertzsprung–Russell diagram is partly named. Observations conducted throughout the 20th century have shown that Polaris has a consistent pulse period of about four days, which has been steadily increasing every year.
View from within the Polaris triple star system; artist's rendering. The North Star is labeled Polaris A. Credit: NASA/ESA/HST, G. Bacon (STScI)
An artist’s conception shows Polaris A with a close companion, known as Polaris Ab. Yet another companion star, Polaris B, can be seen as a speck in the background at right. Credit: STScI