Age of Stars

by Fraser Cain on February 9, 2009

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As you know, everything in the Universe is extremely far away. Even the closest stars take more than 4 years for light alone to reach. Since astronomers can’t actually reach out and sample stars, have you ever wondered how they determine the age of stars, and how long they have to live?

Fortunately, the trusty telescope tells astronomers all they need to know about the age of stars. Essentially, astronomers determine the age of stars by observing their spectrum, luminosity and motion through space. They use this information to get a star’s profile, and then they compare the star to models that show what stars should look like at various points of their evolution. From this, they can determine how old a star is, and how much longer it has to live. This method of determining star age can inaccurate because it relies on the accuracy of the models.

There’s a new technique that was recently developed called gyrochronology, and it’s based on the rotational speed of a star. The speed that a star rotates is steadily changing throughout its life, and it’s dependent on the star’s age and color. If you know a star’s color and rotational speed, you can calculate its age to within an uncertainty of 15%.

Our Sun, for example, has been around for 4.6 billion years, and astronomers think that it should last for another 7 billion years or so before becoming a red giant star.

We have written many articles about stars here on Universe Today. Here’s an article about how older stars seem to lack lithium, and here’s one about how astronomers determined the age of the Milky Way.

If you’d like more information on stars, check out Hubblesite’s News Releases about Stars, and here’s the stars and galaxies homepage.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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