You might expect each latitude of its surface to rotate at roughly the same rate, but it doesn’t. For example, if you could stand at the Sun’s equator, it would take you approximately 24 Earth days to complete one revolution. If you stand at either pole it will take approximately 34 days to return to your original orientation.

This is known as differential rotation and has long puzzled scientists.

As we delve deeper and deeper into the sun, it becomes more and more mysterious. Helioseismological observations show that this phenomenon is not limited to the upper atmosphere, but extends approximately 200,000 kilometers (124,000 mi) across the entire solar convection zone.

Now a team led by solar physicist Juto Becki from the Max Planck Institute for Solar System Research (MPS) has found a clue. The differential rotation appears to be constrained by long-term oscillations of sound waves in the convection zone, detectable on the surface as vortex movements around the poles.

The sun is constantly “buzzing”. The visible surface layer, known as the photosphere, hums with millions of acoustic oscillation modes that rise and fall over a period of about five minutes. We’ve known about these modes for some time, but it wasn’t until a few years ago that a research team led by MPS director Laurent Guizon discovered a new type of acoustic oscillation. Using several years of solar observation data, they found a global oscillation mode with a much longer period of 27 days.

And there was something else. These giant sound waves passing through the Sun appeared to be somehow related to the Sun’s differential rotation.

As recently as 2021, when the original discovery was published, researchers believed that long-term oscillation modes were based on differential rotation. But upon closer examination, Becky and her colleagues found that the relationship works both ways. The differential rotation is interrupted by giant sound waves.

To investigate the connection between the two, he and his colleagues performed three-dimensional numerical simulations examining the effects of the oscillations. The researchers found that high-latitude modes around the poles have a profound effect on the Sun’s behavior by transporting heat from the poles to the equatorial region.

Since the poles are hotter than the equator, this heat transfer limits the temperature difference between the two latitude regions. This means that the contrast between the poles and the equator cannot exceed 7 Kelvin (7 degrees Celsius or 12.6 degrees Fahrenheit). While this difference may be negligible when talking about a ball of hot plasma spinning at thousands of degrees, it is this temperature range that ultimately controls the differential spin.

“This very small temperature difference between the poles and the equator controls the balance of the Sun’s angular momentum and is thus an important feedback mechanism for the Sun’s global dynamics,” explains Gizon.

Although the processes are slightly different, they are similar to how atmospheric instability can cause giant cyclonic storms on Earth. While there’s still a big mystery to solve, the connection between the processes could help us get there. High-latitude oscillation modes play an important role in controlling the Sun’s differential rotation. And perhaps the same dynamics are at work in other stars.

The sun is a large, strange ball of fire in the sky, full of mysteries and mysteries. We are slowly approaching their solutions.