Turns out Hollywood celebs aren’t the only stars who hide their age well – small cool stars are very good at frustrating astronomers’ efforts to determine how old they are, because they essentially look the same for most of their lives.
But now, astronomers have determined that they can accurately judge the age of a star by how fast it is spinning. We know, for example, that stars slow down over time, but it was not until very recently there was no data to support any solid calculations. But, a team of US astronomers have finally done it.
The findings were presented in Seattle at a meeting of the American Astronomical Society by Soren Meibom of the Harvard-Smithsonian Center for Astrophysics (CfA). The details will also appear in the journal Nature.
Astronomers measured the rotation rates of stars by measuring their brightness over time. As sunspot-like features move across the surface of the star, light from the stellar body dims before the dark patch rotates around the target once more. The scientists used data from the original mission of NASA’s Kepler spacecraft. The data was used when the spacecraft was looking for the periodic dimming of stars as their planets passed in front of them.
The scientists were basically looking for another pattern of dimming, which is caused as the dark spots on the surface of the stars rotate in and out of view. These periodic dimmings would shed light on how quickly the star was rotating.
In their new study, the team examined stars in the 2.5-billion-year-old cluster known as NGC 6819. “Older stars have fewer and smaller spots, making their periods harder to detect,” Dr Meibom said.
The astronomers examined stars weighing 80 to 140 percent as much as the Sun. They were able to measure the spins of 30 stars with periods ranging from 4 to 23 days, compared to the present 26-day spin period of the Sun. The eight stars in NGC 6819 most similar to the Sun have an average spin period of 18.2 days, strongly implying that the Sun’s period was about that value when it was 2.5 billion years old.
The scientists then evaluated several existing computer models that calculate the spin rates of stars based on their masses and ages, and determined which model best matched their observations.
“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,” said Barnes from the Leibniz Institute for Astrophysics in Germany.
“Now we can derive precise ages for large numbers of cool field stars in our Galaxy by measuring their spin periods,” states Meibom. “This is an important new tool for astronomers studying the evolution of stars and their companions, and one that can help identify planets old enough for complex life to have evolved.”
Abstract Study Source: http://goo.gl/wsT7dl.