German scientists discover roundest object in Universe

NEW DELHI,Nov18: Scientists from Germany have discovered the roundest known object in the Universe – a hot bright star, some 5000 light years away from Earth.

All rotating bodies like Earth, other planets and stars are slightly flatten. Thus, on Earth, the radius at the Equator is 21 kilometers bigger than the radius measured at the Poles. Similarly, on the Sun, the difference in two radii is about 10 kms. But on the newly measured star, this difference is only three kms. This makes it the most spherical object ever found.

A team of researchers led by Laurent Gizon from the Max Planck Institute for Solar System Research and the University of Gottingen succeeded in measuring the oblateness of the slowly rotating star using asteroseismology – the study of the oscillations of stars. With this, they measured this star’s radii with unprecedented precision. The difference between the equatorial and polar radii of 3 kms is astonishing small compared to the star’s mean radius of 1.5 million kilometers.

“This makes Kepler 11145123 the roundest natural object ever measured, even more round than the Sun,” explains Gizon.

All stars rotate and are therefore flattened by the centrifugal force. The faster the rotation, the more oblate the star becomes. Gizon and his colleagues selected the slowly rotating star, dubbed 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. NASA’s Kepler mission observed the star’s oscillations continuously for more than four years.

Surprisingly, the star is even less oblate than implied by its rotation rate. The authors propose that the presence of a magnetic field at low latitudes could make the star look more spherical to the stellar oscillations. Just like helioseismology can be used to study the Sun’s magnetic field, asteroseismology can be used to study magnetism on distant stars. Stellar magnetic fields, especially weak magnetic fields, are notoriously difficult to directly observe on distant stars.

Kepler 11145123 is not the only star with suitable oscillations and precise brightness measurements. “We intend to apply this method to other stars observed by Kepler and the upcoming space missions TESS and PLATO. It will be particularly interesting to see how faster rotation and a stronger magnetic field can change a star’s shape,” Gizon said adding, “An important theoretical field in astrophysics has now become observational.”
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