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In our solar system, six eggshell-white telescopes, spread out across one of Earth’s verdant mountainsides, peer into the deep universe. The domed structures work as a single, cohesive hive to collect cosmic light to guide modern astronomers as they explore space, and through that hive, we have a brilliant new perspective on the light that guided astronomers of the past: the North Star.
Our current visual knowledge of the North Star (due to the Earth’s axial wobble, the heading passes to different stars (throughout the ages) it goes deep. Artists old and new have depicted Polaris shining in their paintings, astrophotographers have photographed it from their backyards, and scientists have pointed their instruments at it for decades. But the special thing about these new views of Polaris, courtesy of the CHARA Array on Mount Wilson in California, is all about resolution. The special thing about CHARA, as mentioned earlier, is that its telescopes work in harmony with each other. The light data is combined in a central facility to provide a single, sharp image of the source. It’s as if six working telescopes were combining to form a single, final telescope, measuring 330 meters (1,083 feet) in diameter. And so the project’s image resolution—especially the angular resolution—is excellent.
In fact, after examining some of these Polaris images, which were put together with CHARA observations taken between 2016 and 2021, scientists found that to create some previously unknown features of the star. The most notable is that the star has distinguishable spots on its surface, similar to the sunspots we sometimes see on the Sun.
“CHARA images revealed large bright and dark spots on the surface of Polaris that change with time,” said Gail Schaefer, manager of the CHARA Array. expression.
One of the main reasons this finding was surprising is that Polaris isn’t just any old star. It’s a type of star known as a Cepheid variable, meaning it brightens and fades periodically. Polaris, in particular, brightens and dims on a four-day cycle, and scientists love finding Cepheids because of their predictable behavior. That’s because they can be used to measure cosmic distances. Essentially, tracking a Cepheid’s brightness over a cycle can reveal its true brightness.
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In contrast, without predictable periodic pulsations, a star would be unreliable for such measurements. At the risk of oversimplification, a dim star, for example, could be either very far away or simply small — or, for some other reason, strangely dim. Or, It is also possible that the light was dim at the time it was observed.
Going back to these dots, these high-resolution images of Polaris represent “the first glimpse of what the surface of a Cepheid variable looks like,” as the CHARA team puts it. So, finding the dots with this first glimpse was intriguing. But these dots weren’t the only result of the team’s analysis.
Unlike our lonely Sun, Polaris doesn’t wander the universe alone. About 46 times the size of our host star and located 400 light-years away, it’s part of a triple star system. It’s simply the brightest of its siblings. In fact, the original goal of CHARA’s Polaris survey was to map the orbit of the star that orbits our North Star every 30 years. It’s this star that’s much closer, making the endeavor a complex feat. Not only does this star float very close to Polaris, but its companion is also incredibly faint. Its existence wasn’t even confirmed until 2005, when the Hubble Space Telescope was required to document it.
“The small separation and large contrast in brightness between the two stars make the binary system extremely difficult to resolve during its closest approach,” team leader Nancy Evans of the Harvard & Smithsonian Center for Astrophysics, which also helped identify the companion, said in the statement. So the team also looked to some of their other astronomy toolboxes, such as a speckle interferometer at Apache Point Observatory in New Mexico.
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This mission was indeed successful, helping to confirm things like the size of Polaris and suggesting that the star could be about five times more massive than the sun – which is more massive than previously thought. This discovery in itself is significant because, as Evans points out, He told ScienceNewsonly a few Cepheids have had their masses determined. It also raises some interesting questions to investigate in the future. For example, “the combination of mass and distance suggests that the Cepheid is more luminous than evolutionary paths would predict for this mass,” the study authors write.
Still, the spotted nature of the North Star seems to have taken center stage. Consider how the areas of the star where spots are visible and the star’s rotation rate imply a 120-day radial velocity variation—essentially referring to changes in the speed of an object seen along an observer’s line of sight. This raises another puzzle.
“We plan to continue imaging Polaris in the future,” John Monnier, a professor of astronomy at the University of Michigan and co-author of the study, said in a statement. “We hope to better understand the mechanism that creates the spots on Polaris’ surface.”
The study was as follows: It was published In The Astrophysical Journal on August 20.