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.”
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.
The surface of Ceres, whose average diameter is 584 miles, is generally dark and similar in brightness to fresh asphalt. But the dwarf planet does possess 130 mysterious bright areas associated with impact craters that new research suggests are salt-rich areas left behind when briny water-ice from a subsurface layer sublimated in the past.
NASA’s Hubble Space Telescope helped an international team of astronomers find that an unusual object in the asteroid belt is, in fact, two asteroids orbiting each other that have comet-like features. These include a bright halo of material, called a coma, and a long tail of dust.