Research team from the Max Planck Institute for Solar System Research and the University of Göttingen, has measured the oblateness of an extremely slowly rotating star Kepler 11145123, located 5,000 light years away.
(Oblateness refers to the flatness of the star at its poles.)
It has been revealed that the difference between the equatorial and polar radii of Kepler 11145123 is only 3 kilometers (with a precision of 1 km).
Studying the oscillations of stars, researchers used asteroseismology, a technique that helps to reveal the difference between the equatorial and polar radii of the stars.
Stars are not perfect spheres. While they rotate, they become flat due to the centrifugal force and the faster the rotation, the more oblate the star becomes.
This hot and luminous Kepler 11145123 is more than twice the size of the Sun and rotates three times more slowly than the Sun.
It is also significantly more round than the Sun.
NOTE: 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; for the Earth this difference is 21 km.
NASA’s Kepler mission observed the star’s oscillations continuously for more than four years.