Scientists Reveal Age of Sun-Like Stars Via Their Spin

Scientists have devised a new way of revealing the age of Sun-like stars, not relying on acoustic vibrations as in the past, but via their spins, according to recent research.

Stars' ages have long been a well-kept secret, but with this new technique astronomers may be able to identify stars with planets that are as old or even older than our own Sun - that is, around 4.6 billion years of age.

A star's age will also help in the hunt for habitable worlds outside our solar system and shed light on astronomical phenomena involving stars and their companions.

"Our goal is to construct a clock that can measure accurate and precise ages of stars from their spins. We've taken another significant step forward in building that clock," lead author Soren Meibom, of the Harvard-Smithsonian Center for Astrophysics (CfA), said in a statement.

To build this stellar clock, Meibom and his colleagues examined stars in the cluster NGC 6819 weighing 80 to 140 percent as much as the Sun. They were able to measure the spins of 30 stars with periods ranging from 4 to 23 days (our Sun currently has a 26-day spin period).

A star's spin rate can reveal its age because its rate of spin slows down over time - so the slower the star is spinning, the older it is. A star's mass also has something to do with it, as researchers found that larger, heavier stars tend to spin faster than smaller, lighter ones. Given this mathematical relationship, astronomers can easily use a star's mass and spin to calculate its age, with 90 percent accuracy.

But measuring a star's spin is easier said than done. Scientists rely on changes in its brightness caused by dark spots - the equivalent of sunspots - on its surface. Specifically, they watch for the star to dim slightly when a sunspot appears, and brighten again when the sunspot rotates out of view.

"Older stars have fewer and smaller spots, making their periods harder to detect," added Meibom.

Looking at eight Sun-like stars in NGC 6819, which is 2.5 billion years old, the researchers determined that they had an average spin period of 18.2 days. That insinuates that when the Sun was 2.5 billion years old it likely had a similar spin rate.

"Now we can derive precise ages for large numbers of cool field stars in our Galaxy by measuring their spin periods," Meibom said. "This is an important new tool for astronomers studying the evolution of stars and their companions, and one that can help identify planets old enough for complex life to have evolved."

The findings were presented today at meeting of the American Astronomical Society and published Jan. 5 in the journal Nature.

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