‘Gyrochronology’ Allows Astronomers to Find True Sun-like Stars

by Shannon Hall on July 11, 2014

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Credit: NASA/European Space Agency

Our active Sun. Image Credit: NASA / European Space Agency

There’s no doubt the term “Earth-like” is a bit of a misnomer. It requires only that a planet is both Earth-size (less than 1.25 times Earth’s girth and less than twice Earth’s mass) and circles its host star within the habitable zone.

But defining a “Sun-like” star may be just as difficult. A solar twin should have a temperature, mass, age, radius, metallicity, and spectral type similar to the Sun. Although measuring most of these factors isn’t easy, aging a star is extremely difficult, and astronomers tend to ignore it when concluding if a star is Sun-like or not.

This is less than ideal, given that our Sun and all stars change over time. Thankfully a technique — gyrochronology — is allowing astronomers to measure stellar ages based only on spin and find true solar analogues.

“We have found stars with properties that are close enough to those of the Sun that we can call them ‘solar twins,’” said lead author Jose Dias do Nascimento from the Harvard-Smithsonian Center for Astrophysics (CfA) in a press release.

do Nascimento and colleagues measured the spin of 75 stars by looking for changes in brightness caused by dark star spots, rotating in and out of view. Although this difference is minute, clocking in at a few percent or less, NASA’s Kepler spacecraft excels at extracting such small changes in brightness.

On average, the sampled stars spin once every 19 days, compared to the 25-day rotation period of the Sun. This makes most of the stars slightly younger than the Sun, as younger stars spin faster than older ones.

The relationship between stellar spin and age was determined in previous research by Soren Meibom (CfA) and colleagues, who measured the rotation rates for stars in a one-billion-year-old cluster. Since the stars already had a known age, the team could measure their spin rates and calibrate the previous relationship.

Using this method, do Nascimento and colleagues found 22 true solar analogues within their data set of 75 stars.

“With solar twins we can study the past, present, and future of stars like our Sun,” said do Nascimento. “Consequently, we can predict how planetary systems like our solar system will be affected by the evolution of their central stars.”

The results were accepted for publication in The Astrophysical Journal Letters and are available online.

About 

Shannon Hall is an aspiring science journalist and is an editorial intern at Sky & Telescope magazine. She holds two B.A.'s from Whitman College in physics-astronomy and philosophy, and an M.S. in astronomy from the University of Wyoming. This fall she will attend NYU's Science, Health and Environmental Reporting program.

{ 2 comments… read them below or add one }

ursomniac July 11, 2014 at 1:29 PM

I don’t understand.

This is NOT new. The age-activity-rotation relationship for lower Main-sequence stars has been known for over 30 years.

The author would do well to look up papers by Olin Wilson and all of the researchers who worked on the HK Project out of Mount Wilson.

Ianmedeiros July 11, 2014 at 11:35 PM

Ursomniac You wrote well “I don’t understand”. I agree with you that
you DO NOT understand what you are talking about.

-Stars from Mount Wilson survey are not so similar to the Sun (much larger masses and different metallicities) / Bias effect
- There is no true rotation, but projected rotation / bias again
- The authors cited the Olin Wilson papers, so they read the article.

Conclusion: You should shut up and delete this post meaningless.

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