Sun-like stars reveal their ages

Jul 10, 2014 by David A. Aguilar

( —Defining what makes a star "Sun-like" is as difficult as defining what makes a planet "Earth-like." A solar twin should have a temperature, mass, and spectral type similar to our Sun. We also would expect it to be about 4.5 billion years old. However, it is notoriously difficult to measure a star's age so astronomers usually ignore age when deciding if a star counts as "Sun-like."

A new technique for measuring the age of a star using its spin - gyrochronology - is coming into its own. Today astronomers are presenting the gyrochronological ages of 22 Sun-like stars. Before this, only two Sun-like stars had measured spins and ages.

"We have found stars with properties that are close enough to those of the Sun that we can call them 'solar twins,'" says lead author Jose Dias do Nascimento of the Harvard-Smithsonian Center for Astrophysics (CfA). "With solar twins we can study the past, present, and future of stars like our Sun. Consequently, we can predict how planetary systems like our solar system will be affected by the evolution of their central stars."

To measure a star's spin, astronomers look for changes in its brightness caused by dark spots known as starspots crossing the star's surface. By watching how long it takes for a spot to rotate into view, across the star and out of view again, we learn how fast the star is spinning.

The change in a star's brightness due to starspots is very small, typically a few percent or less. NASA's Kepler spacecraft excels at such exacting brightness measurements. Using Kepler, do Nascimento and his colleagues found that the Sun-like stars in their study spin once every 21 days on average, compared to the 25-day rotation period of our Sun at its equator.

Younger stars spin faster than older ones because stars slow down as they age, much like humans. As a result, a star's rotation can be used like a clock to derive its age. Since most of the stars the team studied spin slightly faster than our sun, they tend to be younger too.

This work expands on previous research done by CfA astronomer (and co-author on the new study) Soren Meibom. Meibom and his collaborators measured the rotation rates for stars in a 1-billion-year-old cluster called NGC 6811. Since the stars had a known age, could use them to calibrate the gyrochronology "clock." The new research led by do Nascimento examines free-floating "field" stars that are not members of a cluster.

Since stars and planets form together at the same time, by learning a star's age we learn the age of its planets. And since it takes time for life to develop and evolve, knowing the ages of planet-hosting stars could help narrow down the best targets to search for signs of alien life. Although none of the 22 stars in the new study are known to have planets, this work represents an important step in the hunt for Sun-like that could host Earth-like planets.

The paper was accepted for publication in The Astrophysical Journal Letters.

Explore further: First planet found around solar twin in star cluster

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not rated yet Jul 10, 2014
How can we "define" sun like stars when we don't even know how our own star works?
Uncle Ira
3 / 5 (2) Jul 10, 2014
How can we "define" sun like stars when we don't even know how our own star works?

I might have read him wrong, but I think the article was telling about how they are working on that. Making the definitions better I mean.
5 / 5 (4) Jul 10, 2014
They use comparisons, same as you do when you recognize other humans even if you don't know every detail of how, say, the immune system works.

We do know how star evolution and star innards works on the largest scales, our own especially, same as we do know how biological evolution and cell theory works. It is one of the greatest successes of astrophysics. "Important theoretical work on the physical structure of stars occurred during the first decades of the twentieth century. In 1913, the Hertzsprung-Russell diagram was developed, propelling the astrophysical study of stars. Successful models were developed to explain the interiors of stars and stellar evolution." [ http://en.wikiped...iki/Star ]

That is why the comparison studies are worthwhile, if stars differed too much and we didn't understand why, it would be little value.
not rated yet Jul 11, 2014
"We do know how star evolution and star innards works on the largest scales"
Hey now just settle down. Those theories are pretty sad case for the "greatest successes of astrophysics" This dogma is a major factor in us not having a clue.
If that's not enough to convince you the thermonuclear model is bunk it proves faith defies reason.