Sun-like Stars Reveal How Old They Are with Their Speedy Spins

How old are sun-like stars? That's a good question, and it's one that astronomers have been struggling with for quite some time. Now, scientists have a new technique for measuring the age of a star by using its spin.

Defining exactly what makes a star "sun-like" is difficult. Yet astronomers give these stars that description when they have a temperature, mass and spectral type that's similar to our sun. In theory, this would make the star about 4.5 billion years old. Yet it's difficult to measure the age of a star, so defining whether a star is sun-like or not is also a challenge.

This challenge, though, may have gotten a bit easier. The researchers measured the spin of stars by looking for changes in their brightness caused by dark spots known as starspots crossing the star's surface. By watching exactly how long it takes for a spot to rotate into view, the researchers can learn exactly how fast the star is spinning. Since younger stars spin faster than older ones, this is a good way to measure a star's age.

"We have found stars with properties that are close enough to those of the sun that we can call them 'solar twins,'" said Jose Dias do Nascimento, the lead author of the new paper, in a news release. "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 these central stars."

Since stars and planets form together, learning a star's age can also tell scientists the age of its planets. 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 hunt for signs of alien life.

The findings are published in the journal The Astrophysical Journal Letters.