Polaris is the brightest star in the constellation Ursa Minor and one of the first stars in the sky that many of us knew. Because it is a star that can always be seen in the same position, people in the past even used it as a pointer to give directions.
In the past, both astronomers and the general public have photographed the North Star from many different places and angles. There are photos taken from an observatory to simple photos taken from people's backyards.
But recently, the CHARA array on Mount Wilson in California, USA, has captured the most complete and clearest image of Polaris's surface ever taken. This is revealing a lot about the North Star that we didn't know before.
The most striking feature of Polaris that we didn't know about before is that it has a “spot” on the star's surface. It's similar to the dark spots (sunspots) on the Sun.
“CHARA images reveal large bright and dark patches on Polaris’ surface that change over time,” said Gil Schaefer, CHARA array manager.
However, Polaris is not an ordinary star. It is a type of star known as a Cepheid variable star, or a star that periodically gets brighter and fainter, especially Polaris, which gets brighter and fainter every 4 days.
This feature of Cepheids allows astronomers to use them to measure distances in the universe. Observing how the brightness of a Cepheid changes over time can reveal the star's true brightness.
This high-resolution image of Polaris is “fantastic,” the CHARA team says. “The first image of the surface of a Cepheid variable star.” The discovery of the spots on the surface was interesting, he said. But these spots aren’t the only results from the team’s analysis.
Unlike our only Sun, the North Star does not rotate on its own. It is about 46 times the size of the Sun and is more than 400 light-years away.
Polaris is part of a triple star system and is the brightest star among its siblings.
The imaging team said the mission was a huge success because it helped confirm things like the size of the North Star. The star may be about five times more massive than the Sun, heavier than previously thought, they noted.
This discovery is significant in itself. Since only a few Cepheids have mass, the finding also raises some interesting questions for future investigations. “The combination of mass and distance suggests that Cepheids shine brighter than expected for this mass based on their evolutionary path.”
However, the dot on Polaris seems to have received special attention. The region of the star in which the dot is visible and the star's rotation rate seem to indicate changes in radial velocity, or the change in the speed of an object when viewed along an observer's line of sight. This raises another mystery.
“We plan to continue taking images of the North Star in the future,” said John Monier, a professor of astronomy at the University of Michigan and one of the researchers. “We hope to better understand the mechanisms that create the spots on Polaris’ surface.”
Read the full research here
Compiled from Space.com website
