Starship Asterisk*

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When you're a kid every birthday is cause for celebration, but as you get older they become a little less exciting. You might not want to admit just how old you are. And you might notice yourself slowing down over the years. You're not alone - the same is true of stars. They slow down as they age, and their ages are well-kept secrets. Astronomers are taking advantage of the first fact to tackle the second and tease out stellar ages. ...

Being able to tell the ages of stars is the basis for understanding how astronomical phenomena involving stars and their companions unfold over time.

Knowing a star's age is particularly relevant to the search for signs of alien life outside our solar system. It has taken a long time for life on Earth to attain the complexity we find today. With an accurate stellar clock, astronomers can identify stars with planets that are as old as our Sun or older.

A star's spin rate depends on its age because it slows down steadily with time, like a top spinning on a table. A star's spin also depends on its mass; astronomers have found that larger, heavier stars tend to spin faster than smaller, lighter ones. This new work shows that there is a close mathematical relationship between mass, spin, and age so that by measuring the first two, scientists can calculate the third. ...

For gyrochronology ages to be accurate and precise, astronomers must calibrate their new clock by measuring the spin periods of stars with both known ages and masses. Meibom and his colleagues previously studied a cluster of billion-year-old stars. This new study examines stars in the 2.5-billion-year-old cluster known as NGC 6819, thereby significantly extending the age range. ...

• Nature (online 05 Jan 2015) DOI: 10.1038/nature14118