Stellar angular momentum transport

A star’s core and outer layers need not rotate at the same speed. What transfers spin between them as the star ages?[1]

In a red giant, oscillations can reveal a core rotating faster than the envelope. Which processes redistribute its angular momentum, and at what rates? Asteroseismology uses oscillation frequencies to probe the interior. In slowly rotating stars, rotation splits related mode frequencies; different modes weight the core and outer layers differently. Models combine these shifts to infer internal rotation, then test candidates such as waves and magnetic stresses.[1]

Waves and magnetic fields can explain some measurements. Their roles across different stars are still being worked out.[1]

Successful prescriptions do not provide a complete calibrated theory. The January 2026 magnetic-dynamo preprint studies idealized spherical flow, not a validated transport law for every star.[1] [2]

Rotation influences the mixing of stellar material. That mixing changes the supply of nuclear fuel to the core and the elements a star produces over its life.[1]

Angular momentum transport changes the rotation profile that influences material mixing; the two processes are related but are not identical. Their cumulative effects determine how much fuel is available and what helium and heavier elements remain later. Measurements in different stellar phases therefore test an entire evolutionary history.[1]