Hiding one’s age is not just for vane humans. Low-mass stars, or the so-called “cool” stars, have for many years stymied attempts by scientists to accurately estimate how old they are. Recently, however, researchers report in the journal Nature on how a star’s spin betrays its age.
The new findings suggest that the measurements of the spins of stars can offer information on these very long-lived celestial objects that reside in some of the oldest, most remote parts of the universe. Otherwise, the small cool stars remain roughly the same size and emit an almost constant amount of light over the bulk of their lifetimes. This constancy makes them very difficult to study.
“Let’s imagine that we’re born as small babies, but by our first birthday, we look like an adult, and we stay looking the same through our 20s and 40s and 60s, even 80s, until we suddenly appear old,” said lead author Soren Meibom in a news briefing at the American Astronomical Society meeting taking place in Seattle.
Scientists have known of a correlation between star mass, age, and spin speed, but it is only recently that precision in measuring brightness fluctuations accompanying the spin has been possible. For the study, researchers aimed NASA’s Kepler spacecraft at a patch of sky to watch for the dimming of stars as their respective dark spots rotated into and back out of view. The periodic appearances of the dark spots served to indicate how rapidly the stars were spinning.
The results of the study suggest that older stars spin more slowly than do younger stars. Older stars also had smaller dark spots than did the younger stars observed. Brightness measured over time revealed that emissions “flickered” more dramatically from younger stars than from older stars.