Sun-like Stars Reveal Their Ages b4in.org/p5mu 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. More b4in.org/p5mu
Posted on: Fri, 11 Jul 2014 01:20:55 +0000
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