Size matters, especially if you're a star. Stellar radius and mass are a crucial tool to establish the age of a star, and also the potential habitability of planets around it. One way to size up stars is to look at how they shake, and now a curious system has confirmed that the method is very accurate.
The system, called KIC 9246715, has two red giant stars that have very similar masses (about 2.1 solar masses) and radii (about 8.3 solar radii). The pair forms an eclipsing binary, meaning that from our point of view they regularly get in front of each other. The two stars' revolution is about 171 days.
Since they are so close and big, scientists know their size fairly well. Therefore, in a new study, published in the Astrophysical Journal, astronomers used the system to test a different method. They used asteroseismology to estimate the radius and mass of each star. Asteroseismology looks at the subtle oscillations of stars to work out their properties.
Using data from Kepler, the planet-hunter telescope, they were able to estimate a mass and a radius consistent with the one obtained by the traditional method, which uses Kepler’s third law. This result is very important. The traditional method cannot be applied to single stars but the oscillation method can.
These oscillations are often called starquakes and are generated by turbulence in the deeper layers of stars. Asteroseismology has also been used to investigate the deeper layers and the magnetic fields inside red giants.
The team created a model based on the oscillations we see in our Sun and looked at objects with similar patterns. Kepler has 18 eclipsing binaries where this should apply and KIC 9246715 was the first one observed in detail.
Surprisingly, the system also seems to be quite weird: Only one of the two stars has oscillations. The team thinks that the strong magnetic field of the other somehow dampens the starquakes. The researchers plan to look at the other 17 pairs to understand if this is an unusual feature or something relatively common.