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 celestial pole (less than 1° away) makes it useful for orienteering and navigation. Since the age of modern astronomy, scientists have understood that the star is a binary system consisting of an F-type yellow supergiant (Polaris Aa) and a smaller main-sequence yellow dwarf (Polaris B). Further observations revealed that Polaris Aa is a classic Cepheid variable, a stellar class that pulses regularly.
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.
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
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.As Dr. Torres explained to Universe Today via email, this recently began to change, leading many astronomers to question what is driving Polaris' pulsations."For more than 150 years and up until about 2010, the period had been getting longer by about four or five seconds each year," he said.
To learn more about Polaris' pulsation period, Torres consulted radial velocity measurements going back to 1888. This technique consists of measuring spectra from a
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