All stars rotate and are therefore flattened by the centrifugal force. The faster the rotation, the more oblate the star becomes. Our Sun rotates with a period of 27 days and has a radius at the equator that is 10 kilometres larger than at the poles; for the Earth this difference is 21 kilometres. Gizon and his colleagues selected a slowly rotating star named 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.
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 adds, “An important theoretical field in astrophysics has now become observational.”
The Hapi region of 67P is located between the comet’s two lobes and has proven to be particularly active, displaying a bluish reflectivity spectrum in colour images captured with Rosetta’s OSIRIS camera. This strongly suggests that frozen water is mixed with the dust at the surface.
Astronomers used the 10-metre Keck II telescope in Hawaii to examine a so-called active asteroid, P/2012 F5, that mimics a comet with a tail, but ejects dust like a shot without an obvious reason. The researchers found that it had a very fast spin rate and probably fragmented.
An international team of researchers have found a new way to measure the pull of gravity at the surface of a star. The new method allows scientists to measure surface gravity with an accuracy of about four percent, for stars too distant and too faint to apply current techniques. For remote stars with planets orbiting them, this information is key in determining whether any of those planets can harbour life.