Astronomers Discover Stellar Clock Coded In A Star's Spin

Astronomers have figured out an innovative way to determine the age of the most common stars in the universe -- sun-like cool stars with a relatively low mass -- by using their rates of spin as a yardstick. The findings, published Monday in the journal Nature, allow scientists to accurately calculate the age of these stars, which have been observed to support the vast majority of Earth-like planets.

“A cool star spins very fast when it's young, but just like a top on a table it gets slower and slower as the star grows older,” Soren Meibom from the Harvard-Smithsonian Center for Astrophysics in Massachusetts, and the lead author of the paper, told BBC. However, because the spin of a star is measured using the movement of dark starspots, which are smaller and fewer in number in older stars, it makes determining the age of these stars extremely difficult.

The accurate measurement of spin rate is essential to gauge the age of sun-like stars as most of their measurable properties like size, mass, brightness and temperature remain approximately the same through their entire life. For the purpose of the study, the scientists used data from NASA’s Kepler space observatory, which is equipped with a photometer capable of detecting the periodic dimming of light emitted by distant stars. The scientists tracked the spin of 30 stars, whose spin rates ranged from four days to 23 days, in a 2.5 billion-year-old cluster known as NGC 6819 and discovered that the older a star gets, the slower it spins.

The technique, known as gyrochronology, can be used to determine the age of such older, cooler stars with a less than 10 percent margin of error, a substantial improvement over previous techniques where the margin of error could reportedly be as high as 100 percent.

“We have found that the relationship between mass, rotation rate and age is now defined well enough by observations and is sufficiently supported by the theory that it is possible to obtain the ages of non-cluster stars to within 10 percent,” Sydney Barnes from the Leibniz Institute for Astrophysics in Germany, said, according to a report by Discovery News.

Determining a star’s age is crucial in calculating the age of the planets it supports -- an essential factor in determining whether there might be life on one or more of them.