Researchers think they might have finally explained the mystery of why and how the Sun's rotation is slowing down. The Sun, on normal, rotates on its axis approximately once per month, but two decades ago, researchers made the mysterious discovery that its outer 5 % spins more slowly than the rest of its interior. "Sun would not stop spinning any-time soon, while we have find out that the same solar radiation that heats the Earth is 'braking' the Sun, because of Einstein's Special Relativity, affecting it to gradually slow down, initiating from its surface," writes by the main researcher named ‘Jeff Kuhn’ from the ‘Institute For Astronomy at University of Hawaii. The Sun does not spin as a solid mass like Earth does; instead its portions rotate at different rates depending upon how far they are from the center of the Sun and on their latitude. So the ends will spin at a changed rate to the equator.
That is something we have known for a long-time, but what researchers could not found was, why the outer 5 % of the Sun was rotating slower if compared to its interior. To figure out this different rotation rate, the group looked at 3.5 years of records from ‘NASA's Solar Dynamics Observatory Satellite’, which has been monitoring the Sun since 2010. Their data was taken from the Magnetic Imager and Helioseismic, which looks at solar oscillations in the magnetic field of Sun. They observed that there had been a high-pitched slow-down in the rotation rate of Sun in its outer 150 km layer, which they guess is due to some effect called as photon-braking. The group expects that this photon-braking effect is similar to effect called as Poynting-Robertson, which is a process by which solar radiation results a dust particle orbiting a star to slow-down and lose angular momentum.
They propose that similar effect also acts like a brake on the Sun’s outer area rotation, and perhaps also be in play around other stars in the mighty Universe. According to Jeff Kuhn "This is a moderate torque that is slowing it down, but over the Sun's 5 billion year life-time it has had a very perceptible effect on its outer 35,000 km." The big query now is how this slowing rotation at the surface of Sun disturbs the solar magnetic field, which is what controls the solar flares that blast off the Sun and can disturb Earth's telecommunications. That is something the researchers hope to work on in the future, but we finally have a good awareness about why the Sun's rotation is slowing-down.
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