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posted by martyb on Friday November 18 2016, @12:38PM   Printer-friendly
from the round-round-get-around-I-get-around dept.

Astronomers have measured the roundest known natural object to date using Kepler star oscillation data:

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.

[...] Gizon and his colleagues selected [Kepler 11145123] 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.

Shape of a slowly rotating star measured by asteroseismology (open, DOI: 10.1126/sciadv.1601777) (DX)


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  • (Score: 2) by requerdanos on Friday November 18 2016, @01:13PM

    by requerdanos (5997) Subscriber Badge on Friday November 18 2016, @01:13PM (#428808) Journal

    I wonder whether it's a lack of processes present otherwhere, or additional processes, or conditions that just smooth out processes, that lead to the more nearly circular shape. Any planetary/stellar geologists have a theory?

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  • (Score: 1, Interesting) by Anonymous Coward on Friday November 18 2016, @02:02PM

    by Anonymous Coward on Friday November 18 2016, @02:02PM (#428821)

    Earth is getting rounder and rounder with time[1], supposedly Newton predicted this would lead to rising sea levels as time goes on "...if our earth were not a little higher around the equator than at the poles, the seas would subside at the poles and, by ascending in the region of the equator, would flood everything there."[2] I couldn't find any citation from a legit scholarly source (ie one that practices basic scholarship and says which of Newtons works it came from) for that quote though.

    [1] https://en.wikipedia.org/wiki/Equatorial_bulge [wikipedia.org]
    [2] http://www.mathpages.com/home/kmath182/kmath182.htm [mathpages.com]

  • (Score: 3, Insightful) by bzipitidoo on Friday November 18 2016, @02:19PM

    by bzipitidoo (4388) on Friday November 18 2016, @02:19PM (#428824) Journal

    I supposed it was simply a very slow rate of rotation. The sun's rotational period is 25 days. Maybe this star takes a year or longer.

    At the other extreme is Altair, with one of the fastest rates of rotation known: 8.9 hours.

    • (Score: 2) by requerdanos on Friday November 18 2016, @04:23PM

      by requerdanos (5997) Subscriber Badge on Friday November 18 2016, @04:23PM (#428906) Journal

      I supposed it was simply a very slow rate of rotation.

      In TFA, they say that they picked this star in part because it rotates slowly, but that the rounding is more pronounced than its slower rotation would predict. They theorize something like "magnets" for the difference. But I'm wondering if anyone else had more insight.