Kepler 11145123
The newly discovered Kepler 11145123 star compared with our own Sun Mark A Garlick

The roundest object in the universe has been discovered 5,000 years light years away. The star Kepler 11145123 was found to be almost completely spherical – a highly unusual occurrence in the cosmos.

The star was identified by researchers from the Max Planck Institute for Solar System Research and the University of Göttingen, who measured its oblateness. This refers to the compression of a sphere along a diameter that takes place as a result of its rotation – forces eventually squish it to form an ellipse.

As a result, no stars are perfectly round, and the faster a star rotates, the flatter it gets. For example, our Sun rotates with a period of 27 days and has a radius at its equator 10km (6.2 miles) larger than it is at its poles. Earth rotates once every 24 hours and has a 21km (13-mile) difference between the equator and poles.

Kepler 11145123 is twice the size of our Sun and rotates three times slower. As a result, the difference between the radius at the equator and its poles is just 3km (1.86 miles) – an incredibly tiny difference, considering its huge size.

"This makes Kepler 11145123 the roundest natural object ever measured, even more round than the Sun," said Laurent Gizon, author of the study published in Science Advances.

The team made the measurements using Nasa's Kepler spacecraft. They observed the star's oscillations for over four years. As well as its very slow rotation, the team believes its roundness could come from a magnetic field at low altitudes, which may make the star appear more spherical.

Scientists now plan to use their method to study other stars observed with Kepler. "This work is a first step in the study of stellar shapes through asteroseismology," they wrote. "The method demonstrated here will be applied to other stars, including more rapidly rotating stars and stars with stronger magnetic fields, where deformations will be greater. Because of the unprecedented high precision and long time span of the Kepler observations, an important field of theoretical astrophysics is now also observational."