Astronomers say that they have managed to spot the roundest object ever observed in nature – a star that is located 5,000 light-years away.
Published in the journal Science Advances, the study that describes the discovery notes that the difference between the equatorial and polar radii of the star is only 3 kilometers and compared to the mean radius of the star which is 1.5 million kilometers, this difference is astonishingly small making the star the roundest object ever observed in nature.
There are quite a few reasons why this particular discovery is quite important. First and foremost is the technology and method called asteroseismology, which is the study of oscillations of stars, using which astronomers were able to measure the stellar oblateness in unprecedented detail.
A team of researchers led by Prof. Laurent Gizon from the Max Planck Institute for Solar System Research (MPS) and the University of Göttingen explain that as stars rotate they are flattened by the centrifugal force. The faster the rotation, the more oblate the star is. Our Sun rotates with a period of 27 days and has a radius at the equator that is 10 km larger than at the poles. Gizon and his colleagues selected a slowly rotating star named Kepler 11145123. This hot and luminous star is more than twice the size of the Sun and rotates three times more slowly than the Sun.
The team selected this particular star because it supports purely sinusoidal oscillations. The periodic expansions and contractions of the star can be detected in the fluctuations in brightness of the star. NASA’s Kepler mission observed the star’s oscillations continuously for more than four years. Different modes of oscillation are sensitive to different stellar latitudes. For their study, the authors compare the frequencies of the modes of oscillation that are more sensitive to the low-latitude regions and the frequencies of the modes that are more sensitive to higher latitudes. This comparison shows that the difference in radius between the equator and the poles is only 3 km with a precision of 1 km.
“This makes Kepler 11145123 the roundest natural object ever measured, even more round than the Sun,” explains Gizon.