video: In this video you are placed inside a simulation of the interior of a solar-type star. The red and blue shapes represent the turbulent convective motions that animate the external shell of the Sun, which covers 30% of its radius. Inflow (blue) and outflows (red) change properties from the equator to the pole due to the influence of the global rotation of the star. The turbulent motions inside the Sun generate a large-scale magnetic field, which is represented by the white-blue tubes (color represents the polarity of the magnetic field). Two main structures emerge, one in each hemisphere. While the convective cells typically live for about a month, this magnetic field reverses (i.e. changes sign) on a decadal time-scale, as shown by the time-lapses in the video. This reversal is regular and occurs because of the non-linear modulation by magnetic torques of the large-scale flows inside the turbulent convection zone. By carrying out a series of such simulations, we show that the magnetic cycle directly depends on the rotation rate and luminosity of the star, which can be expressed as a function of only one parameter, called the Rossby number. NOTE: This is a medium size file, best-viewed by powerful smartphones. If you do not have access to a VR headset, you may visualize this file on your computer with the 'Gopro VR Player,' which you may download. The movie must be viewed in 'mono' mode (no stereoscopy), using an equirectangular projection (it is the default setting for most VR headset and softwares). This material relates to a paper that appeared in the July 14, 2017 issue of Science, published by AAAS. The paper, by A. Strugarek at Université de Montréal in Montréal, QC, Canada, and colleagues was titled, "Reconciling solar and stellar magnetic cycles with nonlinear dynamo simulations." view more
Credit: University of Montréal - DAp/CEA - AIM
据新的研究声称，太阳是一种具太阳能类型的恒星（solar-type star），该研究解决了一个有关在太阳系中心的这颗恒星是否会表现出与其它附近太阳类恒星相同的周期性行为的持续存在的争议。这些结果还推进了科学家对恒星如何产生其磁场的了解。太阳的活动（包括太阳辐射程度的变化及太阳物质的喷射）会在一个长11年的周期中发生变化，其变化的驱动力是其磁场的改变。这一周期性变化是太阳物理学中遗留下的重大谜团之一，其部分原因是因为它似乎不能映照其它太阳类恒星的磁场周期变化，这使得有些人提出，太阳并非太阳类恒星。在这里，通过对恒星磁场进行一系列的模拟，Antoine Strugarek和同事显示，太阳的磁场周期变化取决于其旋转速度和发光度（它们间的关系可用所谓的罗斯贝数函数来表达；事实上，他们证明，太阳的磁周期与该数字成反比）。作者将他们的模拟结果与遥远恒星采样中的可得到的周期活动观察进行了比较，他们进一步发现，他们在太阳周期与罗斯贝数之间所确立的关系与他们在其它太阳类恒星中所观察到的周期变化相符。这些结果确认，太阳确实是一颗太阳类恒星。
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Journal
Science