News By Jan. 8, 2015 7:31 am
Astronomers could learn the age of a star by how fast it spins | News |

Much of the work astronomers do is astonishingly accurate. They use reliable yardsticks like the speed of light or the influence of gravity, quantities we can measure on Earth under the reasonable assumption that those measurements will apply everywhere else in the universe. However, sometimes the evidence used is much more fuzzy, and theory has more to do with logical deduction than hard mathematics.

Up until very recently, that had been the case with a niche technique called gyrochronology, or the determination of a star’s age by its rate of spin. Astronomers knew that our Sun is roughly 4.6 billion years old and spins once every 26 Earth days, and that very young stars aged a billion years or less spin every 7-10 days — but beyond that? There simply weren’t enough data points to construct a working age-to-spin formula, and gyrochronology was largely restricted to statements like “Older than 1 billion, younger than 4.” But with the help of all new observations from the Kepler observatory, that may be about to change.

Kepler, you may remember, is NASA’s designated planet-hunter. Specifically, it excels at looking straight into a burning star and resolving detail through the excess light, which is why it can spy planets as dark spots moving against the lighted background. Well, this shadow-finding ability applies just as well to other dark spots on or near stars, including sunspots, and so Kepler was the perfect tool for measuring rotational speed of a star. Sunspots provide a surface reference point for measuring spin speed, and the Kepler observations have led to reporting of the spin-related age of 22 new stars throughout the age spectrum. Now, with a much more reliable way to observe spin speed, stellar age might become a relatively easy metric for astronomers to measure.

Astronomers could learn the age of a star by how fast it spins | News |

Kepler, now largely broken but still a valuable part of NASA’s arsenal.

This technique only works with so-called main sequence stars, like our own Sun. The principle underlying the spin aging process, that stars spin more and more slowly as they age, does not hold for freakish stars, extremely young stars, or stars that have lived too long and become white dwarfs, red giants, or enormous supernovae. That’s actually not such a big drawback, especially since all of Kepler’s planetary data seems to be telling us that relatively cool, main sequence stars are host to the vast majority of Earth-like planets. Astronomer and the popular culture are obsessed with alien life these days, and so any info that helps us narrow the candidates for life-finding investigations will be important going forward.

Astronomers could learn the age of a star by how fast it spins | News |

Note that this is a rough enough way of determining age that it’s really more estimation than measuring; the error has been reduced to an impressive 10% — far better than we’ve been able to do before without intense scrutiny of a star, but only really good enough for general categorization of stars. As mentioned, that will help NASA avoid wasting time in the future, as it sifts through the enormous and quickly growing database of planets it could survey for signs of life.

We’ve got rovers searching Mars for signs of ancient microbes, government bodies setting their sights on Europa, and NASA developing newly advanced methods of searching far-away stars as well; truly, this is a future Carl Sagan would have been happy to see.

Now read: Kepler discovers 8 new planets, one is the most Earth-like yet

Astronomers could learn the age of a star by how fast it spins | News |


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