Stars are not perfect spheres. While they rotate, they become flat due to the centrifugal force. A team of researchers around Laurent Gizon from the Max Planck Institute for Solar System Research and the University of Göttingen has now succeeded in measuring the oblateness of a slowly rotating star with unprecedented precision. The researchers have determined stellar oblateness using asteroseismology - the study of the oscillations of stars. The technique is applied to a star 5000 light years away from Earth and revealed that the difference between the equatorial and polar radii of the star is only 3 kilometers - a number that is astonishing small compared to the star's mean radius of 1.5 million kilometers; which means that the gas sphere is astonishingly round.

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 km larger than at the poles; for the Earth this difference is 21 km. 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.

Gizon and his colleagues selected this star to study because it supports purely sinusoidal oscillations. The periodic expansions and contractions of the star can be detected in the fluctuations in brightness of the star. NASA's Kepler mission observed the star's oscillations continuously for more than four years. Different modes of oscillation are sensitive to different stellar latitudes. For their study, the authors compare the frequencies of the modes of oscillation that are more sensitive to the low-latitude regions and the frequencies of the modes that are more sensitive to higher latitudes. This comparison shows that the difference in radius between the equator and the poles is only 3 km with a precision of 1 km. "This makes Kepler 11145123 the roundest natural object ever measured, even more round than the Sun," explains Gizon.

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."

Quote from: Azendac on November 16, 2016, 09:43:32 PM

Quote from: Winy on November 16, 2016, 09:24:02 PM

Just because I love talking about stuff like this, I also want to mention Vega, which is part of the Summer Triangle, the same asterism that Deneb is a part of (I mention it because it's in the artist's rendition included in the article). In contrast to the star mentioned in the OP, Vega's rotation is extremely fast, causing it to have a significant bulge at the equator. In fact, it's rotational velocity has been measured to be roughly 88% of the speed required for the star to begin ripping itself apart because of centrifugal effects (About 236km/s). The rapid rotation causes the equator to extend 19% further than the poles of the star.

Just throwing out some cool information I thought people might be interested in if they like the article.

Space stuff gets my dick hard, I make sure to check space.com and astronomy.com every other day for cool stuff.

I mean, I sort of have to keep up with it, it's my major.

Quote from: Azendac on November 16, 2016, 09:56:43 PM

That's pretty awesome, do you get special access to observatories or talks with people in the field? I'm not actually sure what an astronomy degree entails right now.

My school has a campus observatory that's used for research purposes, but it's also open to the public most days of the week and ran by the astronomy club. Weirdly enough, I've never actually been up there (Mostly because it's like a half-hour walk away, and I'm a very, very busy student). I can certainly talk with people involved in the field, because my professors all do research at the school in some form.

Most astronomy majors are in it so that they can earn Ph.Ds and get into the research themselves, but I'm not really interested in that. I want to be a science teacher when I get older, so I'll graduate with a BA in Astronomy, as opposed to a BS, which is what people who want to go to graduate school generally pursue. Research is great, but it's not the life I want. Involves a lot of travel, and the level of rigor involved in the schooling would probably drive me mad.