Stellar Girocronologia

At the 225th meeting of the ACD, which is taking place these days in Seattle, a group of researchers led by Soren Meibom from the CfA, presented the results of their study on the application of a method that will allow us to determine more accurately the age of the stars. It is a new, important research tool that astronomers can use not only to study the evolution of the stars but also to identify those planets evolved enough where there may be complex life forms.


Credit: David A. Aguilar (CfA)

When we are young we do not wait to celebrate our birthdays, but as we get older the festivities become less and less interesting. Usually, we do not ever want to admit our age and there are more and more lenses over the years. However, we are not alone because this is also true for the stars. In fact, they slow down as they age and their age is held in secret. Today, astronomers are taking advantage of the first fact to derive valuable clues on the second, with the aim of revealing just the age of the stars.
“Our goal is to build a kind of clock that allows to accurately measuring the age of the stars from the spin,” says Soren Meibom from the Harvard-Smithsonian Center for Astrophysics (CfA). “We made a further step towards the construction of this watch.” Meibom presented the results obtained by his group in a press conference held on the occasion of the 225th meeting of the American Astronomical Society that is taking place these days at the Washington State Convention Center in Seattle, USA.
The rotation of a star depends on its age since it slows down continuously in the course of its evolution, a bit like when a cap by turning quickly on a table begins to slow down and then stop. Moreover, the spin also depends on its mass: astronomers have indeed found that larger and more massive objects tend to rotate faster than the smaller and less massive stars. This study shows that there is a mathematical relationship between the mass, spin, and the age of the star so by measuring the first two parameters can be derived on the third. “We found that the relationship between the mass, rotation and age is now well defined by the observations to the point that we are able to obtain the age of the individual stars with an accuracy of 10%,” says Sydney Barnes the Leibniz Institute for Astrophysics in Germany and co-author of the study. In 2003, Barnes first proposed this method he called girocronologia.
To calculate the spin of a star, scientists must monitor changes in brightness caused by the presence of dark spots, that is the equivalent of sunspots, which appear on the surface. But unlike the Sun, a distant star appears as a bright dot therefore becomes difficult to directly observe a stain that crosses the stellar disk. To avoid this, astronomers have come up with a method: they measure the weak variation of brightness that decreases when a stain appears and returns to the initial value when it disappears because of the stellar rotation. More details will be published in the part two of this article.

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