Fast core rotation in red-giant stars revealed by gravity-dominated mixed modes

Understand

When the core hydrogen is exhausted during stellar evolution, the central region of a star contracts and the outer envelope expands and cools, giving rise to a red giant, in which convection occupies a large fraction of the star.

• Conservation of angular momentum requires that the cores of these stars rotate faster than their envelopes, and indirect evidence supports this.
• Information about the angular momentum distribution is inaccessible to direct observations, but it can be extracted from the effect of rotation on oscillation modes that probe the stellar interior.
• Here, we report the detection of non-rigid rotation in the interiors of red-giant stars by exploiting the rotational frequency splitting of recently detected mixed modes.