Perfect star: Astronomers find roundest object in the universe

MUNICH, Germany, Nov. 16 (UPI) -- Scientists have found the roundest object in the universe. The object is Kepler 11145123, a star 5,000 light-years from Earth.

The rotational velocity of most stars and planets pushes material toward the equator, making most celestial objects flat. The faster they spin, the greater the object's centrifugal force. The greater the centrifugal force, the flatter the object becomes.

Astronomers measure an object's relative flatness by calculating the difference between an object's equatorial and polar radii.

For Kepler 11145123, which rotates extremely slowly, the difference is three kilometers. The sun, which completes a rotation every 27 Earth days, boasts a difference of 10 kilometers. Earth is even flatter, with a difference of 21 kilometers.

Scientists at the Max Planck Society for the Advancement of Science were able to measure the equatorial and polar radii of Kepler 11145123 by observing its oscillations. Astronomers observed the star's pulsing luminosity for four years.

Their observations revealed two oscillation modes, each oriented with different latitudes. Analysis of the frequency shifts during the low-latitude oscillations and frequency shifts during the higher-latitude pulses revealed a radii difference of three kilometers.

"This makes Kepler 11145123 the roundest natural object ever measured, even more round than the Sun," researcher Laurent Gizon explained in a news release.

The star is rounder than its rotational velocity suggests. Astronomers believe a low-latitude magnetic field may play a role in maintaining the star's rotundity. The revelation suggests radii differences could be used to study magnetism on faraway stars.

"We intend to apply this method to other stars observed by Kepler and the upcoming space missions TESS and PLATO," Gizon said. "It will be particularly interesting to see how faster rotation and a stronger magnetic field can change a star's shape. An important theoretical field in astrophysics has now become observational."