Astronomers have identified the roundest object measured in the universe. The object, a distant star located about 5,000 light-years away from planet Earth, is more than twice the size of the sun but is significantly more round.

Stars And Planets Not Perfectly Spherical

Stars and planets are not perfect spheres. These celestial objects flatten out in the middle when they rotate because of centrifugal force. As the faster planets and stars spin, the greater is their centrifugal force. Objects tend to become flatter with greater centrifugal force.

To determine the relative flatness of an object, astronomers calculate the difference between the object's polar and equatorial radii. The sun, which makes a complete rotation every 27 Earth days, has a difference of 10 kilometers. The Earth, which is flatter, has a difference of 21 kilometers.

Roundest Natural Object Ever Measured

Using a technique called asteroseismology, which studies the oscillation of a star, researchers found that the star Kepler 11145123 only has a difference of 3 kilometers between its equatorial and polar radii, a number astonishingly small relative to the star's mean radius of 1.5 kilometers, which means that the star is very round.

"This makes Kepler 11145123 the roundest natural object ever measured, even more round than the Sun," said study researcher Laurent Gizon from the Max Planck Institute for Solar System Research.

Influence Of The Star's Magnetic Field

Astronomers observed the star's pulsing luminosity over a period of four years. The observation revealed of two oscillation modes individually oriented with different latitudes. Analysis of the frequency shifts during low-latitude oscillations and higher-latitude pulses revealed the star's radii difference.

The researchers think that a low-latitude magnetic field possibly plays a role in maintaining the star's rotundity. The findings also suggest that radii differences may be used to study magnetism on distant stars.

"Because the observed ΔR/R is only one-third of the expected rotational oblateness, we conjecture the presence of a weak magnetic field on a star that does not have an extended convective envelope," the researchers wrote in their study published in Science Advances.

Asteroseismology To Be Used To Study Other Stars

Gizon and colleagues said that they plan to use the method they applied to study Kepler 11145123 on other stars that are observed by Kepler space telescope and future space missions PLATO and TESS. NASA's Kepler space observatory was launched in 2009 to discover Earth-size planets that orbit other stars.

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