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article imageSun spins faster on the outside than on the inside

By Tim Sandle     Jan 5, 2017 in Science
Despite being relatively close to Earth and a well-studied phenomenon there is still much to learn about the Sun. New research by international astronomers has helped to make an important new discovery about our closest star.
The discovery came about after astronomers were reviewing data provided by NASA’s Helioseismic and Magnetic Imager, which is located on-board NASA’s Solar Dynamics Observatory. The data reviewed was accumulated over several years. The Solar Dynamics Observatory is a NASA mission which has been observing the Sun since 2010. The observatory a 3-axis stabilized spacecraft, with two solar arrays, and two high-gain antennas, in an inclined geosynchronous orbit around Earth.
The area of interest was to try to understand why the outermost layer of the Sun rotates approximately five percent more slowly than the interior of the star. The answer, the website Science reports, is that the scientists have come up with is that each time the Sun blasts out energy and material from its surface this imposes, in terms of classical physics, an equal and opposite force upon the Sun. These physical forces help to slow the rotation of the Sun’s outermost layer.
Discussing the matter further with Laboratory Roots magazine, the lead investigator Dr. Jeff Kuhn adds: “The Sun won't stop spinning anytime soon, but we've discovered that the same solar radiation that heats the Earth is 'braking' the Sun because of Einstein's Special Relativity, causing it to gradually slow down, starting from its surface.”
The researcher comments further by stating: "This is a gentle torque that is slowing it down, but over the Sun's five billion-year lifetime it has had a very noticeable influence on its outer 35,000km," Kuhn continued.
The figure about the difference with the spinning is relative to how deep into the surface of the Sun a reading is taken. Here the Sun rotates two percent more slowly 100 kilometers from the surface and five percent more slowly around 30,000 kilometers from the surface.
The reason partly relates to the Sun’s structure. Unlike many planets or solid masses, the Sun is a giant nuclear reactor. This allows for it to rotate more freely than solid objects and the rotation varies in relation to how far an area is away from the core of the Sun.
The research has been published by arXiv.org and it is titled “A Poynting-Robertson-like drag at the Sun's surface.”
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