A better model for star aging

With current methods, it's much easier to determine the ages of stars in clusters, such as NGC 1783, as pictured here by the Hubble Space Telescope(Credit: NASA/ESA)

Working out the age of any given star in the night sky can be a very difficult task, and estimates are easier to make based on readings from groups rather than individual objects. A new model might significantly improve the situation, providing a conceptual framework to explain the rotation of stars, the intensity of their stellar winds and their X-ray emissions, arriving at a much more accurate estimate of age.

With current models, determining stellar age can be difficult. Astronomers have an easier time working out the age of stars residing within clusters, using mutual properties to obtain enough data to make an estimate, but those figures can be rather inaccurate, with a margin of error up to 25 percent – often equal to billions of years.

Working out the age of a star that's not in a cluster is even more difficult. There's less data to go on, so astronomers calculate the age based on known factors, such as the fact that older stars spin more slowly, or have lower X-ray luminosities. A team from the University of Rochester believed that it could improve the situation, creating a much more advanced system that brings together observable data and astrophysics theory.

The new model is designed to bring data together, working out how rotation, magnetic fields, X-ray activity and loss of mass are linked and affect one another. Most previous approaches have only looked at these factors individually or in pairs, but by looking at the complete problem, the new model can, the researchers believe, much more accurately determine stellar age.

Specifically, the model is designed to analyze stars with a similar mass and radius to our own Sun, which was used as a calibration point during development. The model is still a work in progress, but it's already revealing important information about Sun-like stars.

"Our model shows that stars younger than our Sun can vary quite significantly in the intensity of their X-ray emission and mass loss," said lead author Eric Blackman. "But there is a convergence in the activity of the stars after a certain age, so you could say that our Sun is very typical for stars of its mass, radius, and its age. They get more predictable as they age."

The findings of the work are published online in the Monthly Notices of the Royal Astronomical Society.

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