Physicists have long known that the Sun, like the Earth, rotates. Decades ago, they realized that the Sun's surface was rotating a little slower than their models predicted, which became a kind of signal that something was wrong. After that, a detailed study of the luminary began, and many scientists began to doubt that they actually understood how the sun behaves.
The team of astronomers watched the star long enough to believe they have identified the source of the slowdown. The hypothesis looks quite elegant, but many are skeptical about it, considering the theory to be highly speculative. But if the assumption turns out to be correct, then astronomers can claim that they have discovered some features common to all stars in the universe.
The sun is not an easy subject to study. Most of its outer layer rotates uniformly, resembling a ball surrounded by a seething turbulence called the convective zone. The relatively thin (only 500 km thick) layer that emits light rotates more smoothly, and the outer 70 km layer rotates about 5% slower than its inner counterparts, according to the American Physical Society. According to astronomer Jeff Kuhn, who was not involved in the study, this behavior is very unusual and does not correspond to modern theories of the physics of convection and turbulence. Why is the region, which seems to be very stable at first glance, so slow?
The theory of scientists is even too simple: if the sun rotates, then it emits particles at an angle. These particles will also produce a rotational force (so-called torque), which over time leads to a slight deceleration of the outer layer. The easiest way to see this effect is with a garden sprinkler: usually the movable sprinklers rotate in the same direction as the water jets. But if a really heavy (and the Sun has a huge mass) sprinkler is pre-rotated in the opposite direction, then the water drops will significantly slow down its rotation. And if the sun slows down like this, then all the stars behave, says Kuhn.
Astronomers have made many observations in order to confirm the hypothesis with facts, and in this they were helped by NASA's Solar Dynamics Observatory satellite. They calculated the speed of rotation of the Sun's outer layer by tracking how acoustic waves (analogous to earthquakes on Earth) travel from the surface of a star to its core and back. This allowed the researchers to carry out detailed measurements of the torque, which were published in Physical Review Letters.
Other physicists believe that while the calculations themselves are of sufficient interest, the hypothesis as a whole is rather speculative. The calculations clearly lack data on the viscosity and the nature of the gaseous medium inside the Sun (it is currently not possible to measure it), and therefore the deceleration could arise simply due to the fact that turbulence slightly increases the viscosity of the plasma.