Stars may look calm and steady in the night sky, but deep inside they are constantly moving and changing.
One of the most important changes is how fast they spin. From the time they are born to the end of their lives, most stars gradually slow down.
Scientists call this process “spin down,” and it can reduce a star’s rotation speed by 100 to 1,000 times over its lifetime.
Our own Sun is a good example. Over billions of years, it has lost energy and slowed its rotation as charged particles stream away from its surface in what is known as the solar wind.
Astronomers believe that magnetic fields interacting with this flowing material play a key role in slowing stars down.
However, exactly how this process works inside stars has remained a mystery.
In recent years, a technique called asteroseismology has given scientists a new way to explore stars.
By studying tiny vibrations inside stars, researchers can measure how different layers rotate and even estimate their magnetic fields.
These observations have revealed that stars may slow down more dramatically than current theories can explain.
Curious about this, a team of researchers at Kyoto University decided to take a closer look at what happens inside massive stars. Their findings were published in The Astrophysical Journal.
Using powerful 3D computer simulations, the team recreated the extreme conditions inside a massive star. Inside these stars, hot gas moves in a process called convection, creating powerful currents that interact with rotation and magnetic fields.
These interactions are complex and constantly changing.
The researchers found that rotation, magnetic fields, and convection are closely linked and influence each other over time. This relationship is similar to the process that generates the Sun’s magnetic field, known as the solar dynamo. By modeling these interactions, the team was able to predict how a star’s internal rotation changes as it evolves.
One surprising discovery was that stars do not always slow down. While many stars lose speed over time, certain magnetic field patterns can actually cause parts of a star—especially its core—to spin faster. In other words, some stars can “spin up” instead of slowing down.
This means that a star’s final rotation speed depends on its unique internal conditions, especially the shape and strength of its magnetic fields. In some cases, very slow rotation may not even be possible for certain types of massive stars.
These findings suggest that the processes controlling rotation in stars like our Sun may also apply to much larger stars. This could help scientists better understand how stars evolve and what happens just before they die.
In the future, the research team plans to simulate the full life cycles of stars of different sizes. By doing this, they hope to predict how stars spin at every stage of their lives, giving us a clearer picture of how these distant objects live, change, and eventually come to an end.
Source: KSR.
