New details about the size and appearance of the North Star

By Amit Malewar 21 Aug, 2024

Collected at: https://www.techexplorist.com/new-details-size-appearance-north-star/87479/

Earth’s North Pole points to a direction in space marked by the North Star called Polaris. In addition to being a helpful guide, Polaris is a spectacular star in its own right. It is a pulsating variable and the brightest star in a triple-star system. The star’s diameter increases and decreases throughout a four-day cycle, making Polaris intermittently brighter and fainter.

Using Georgia State University‘s Center for High Angular Resolution Astronomy (CHARA) Array, scientists have identified new details about the size and appearance of the North Star, also known as Polaris.

Polaris is a kind of star known as a Cepheid variable. Astronomers refer to these stars as “standard candles” since their actual brightness varies according to their pulsation period: Compared to fainter stars, brighter stars pulse more slowly. The distance to a star and its brightness determine how bright the star looks in the sky.

Astronomers may use Cepheids to measure the distances to their host galaxies and assess the rate at which the universe expands since we can determine the actual brightness of a Cepheid based on its pulsational period.

A team of astronomers led by Nancy Evans at the Center for Astrophysics | Harvard & Smithsonian observed Polaris using the CHARA optical interferometric array of six telescopes at Mount Wilson, Calif. The investigation aimed to map the orbit of the close, faint companion that orbits Polaris every 30 years.

Nancy Evans at the Center for Astrophysics | Harvard & Smithsonian said, “The small separation and large contrast in brightness between the two stars makes it extremely challenging to resolve the binary system during their closest approach.”

At the famous Mount Wilson Observatory, the CHARA Array combines the light from six telescopes arranged over the mountaintop. The faint companion traveled close to Polaris, and the CHARA Array used its combined light to detect it like a 330-meter telescope. The MIRC-X camera, developed by astronomers at Exeter University in the United Kingdom and the University of Michigan, recorded Polaris observations. The MIRC-X camera is remarkably good at capturing stellar surface details.

The group was able to measure variations in the Cepheid’s size throughout its pulsations and successfully trace the close companion’s orbit. Based on its orbital speed, Polaris has a mass five times greater than the Sun. According to pictures of the object, Polaris’s diameter is 46 times larger than the Sun.

The biggest surprise was Polaris’s appearance in close-up images. Observations from CHARA offered the first glimpse of the surface of a Cepheid variable.

“The CHARA images revealed large bright and dark spots on the surface of Polaris that changed over time,” said Gail Schaefer, director of the CHARA Array. The presence of spots and the star’s rotation might be linked to a 120-day variation in measured velocity.

“We plan to continue imaging Polaris in the future,” said John Monnier, an astronomy professor at the University of Michigan. “We hope to understand better the mechanism that generates the spots on the surface of Polaris.”

Journal Reference:

1. Nancy Remage Evans, Gail Schaefer et al. The Orbit and Dynamical Mass of Polaris: Observations with the CHARA Array. The Astrophysical Journal. DOI 10.3847/1538-4357/ad5e7a