Cepheids are stars that pulse at regular intervals in diameter and brightness, but Polaris is part of a binary system, having a dimmer teammate known as Polaris B, which is also visible from Earth.
Different Techniques to Study the Star
The issue with Polaris is that researchers cannot estimate how big or distant it is. Astrophysicists have a few techniques with which they can calculate the mass, age, and distance of a star like Polaris. One of those methods is a stellar evolution model, according to the new study co-author Hilding R. Neilson, an astrophysicist at the University of Toronto.
Scientists can analyze the brightness, color, and rate of pulsation of the star and utilize that information to figure out its size and brightness level, as well as what stage of life it is in. After these details are applied, it is not difficult to figure out how far away the star is, Nelison said.
These models are especially accurate for cepheids because their pulsing pace is straightly related to their luminosity. That makes it easy to estimate the distance of any of these stars, and astronomers are incredibly sure they understand that the correlation: that cepheids have become vital elements in measuring distances all over the Universe.
There are a few other ways to analyze Polaris, and those techniques do not agree with the stellar evolution models.
“Polaris is what we call an astrometric binary,” Neilson said, “which means you can actually see its companion going around it, sort of like a circle being drawn around Polaris. And that takes about 26 years.”
Scientists have not yet made accurate observations of a full circuit by Polaris B, but they have seen sufficient of the counterpart star in recent years to have a quite detailed image of what the orbit looks like. According to Nelison, the team can use Newton’s laws of gravity to measure the masses of the binary system.
Polaris is Extremely Difficult to Study
That information, besides new Hubble Space Telescope ‘parallax’ measurements, results in very accurate numbers on Polaris’ mass and distance. Those calculations say it is approximately 3.45 times the mass of the Sun, which is about 0.75 solar masses. More calculations revealed the fact that the star is much older than its pair, which is rather unusual for a binary system. Normally, the two stars are about the same age.
Nelison and Haley Blinn, an undergraduate student and researcher at the University of Toronto, produced numerous models of Polaris to see whether those templates could adjust all the information known about the system, but they couldn’t.
A possibility is that some o the measurements were wrong, the scientists wrote in the paper, mostly because Polaris is an especially difficult star to analyze. However, the data researchers have seemed reliable, and there is no definite reason to doubt that information, Nelison said.
“It is challenging to draw significant conclusions beyond the fact that Polaris continues to be an enduring mystery, and the more we measure, the less we seem to understand,” Neilson and Blinn wrote.