Cause of stalled stellar spin-down

Determine the physical cause of slowed or completely stalled stellar spin-down, including whether angular-momentum redistribution from the stellar core to the convective envelope offsets angular-momentum loss through magnetized stellar winds.

Background

The paper finds that stellar spin-down can become slowed or stalled over particular mass and age ranges, with the phenomenon appearing to propagate as a function of both stellar mass and age. The authors discuss angular-momentum transfer from the core to the convective envelope as one possible explanation: core angular momentum may replenish the envelope while magnetized stellar winds remove angular momentum from the surface.

The physical treatment remains phenomenological because the core-envelope coupling timescale is held constant during stellar evolution. Establishing the mechanism responsible for stalled spin-down is important for modeling stellar rotational evolution and for determining when gyrochronology can reliably infer stellar and cluster ages.

References

This effect must be accounted for in order to accurately model the rotational evolution of young stars, however the cause of this slowed, or completely stalled spin down is still unclear.

— NGTS clusters survey - VI: Stellar rotation in seven young open clusters within the PLATO LOPS2 field  (2608.27170 - Hughes et al., 27 Aug 2026) in Section 5.2, “Stalled spin down as a function of mass”

At the same time, several open questions remain, including possible changes in rotational spin-down, the reliability of chemical clocks, and the limited overlap between asteroseismic and gyrochronological age samples.

— Open Clusters as Laboratories for Cool Star Evolution: Highlights from the Cool Stars 23 Splinter Session  (2609.09026 - Chahal et al., 8 Sep 2026) in Section 7, Summary and Future Outlook

In this respect, new observations particularly targeting stars more evolved than the Sun are essential to determine whether the rescaling between the theoretically inferred and the semi-empirically derived $\dot{J}_{\rm wind}$ still applies for more evolved objects.

— Detailed study of HD 219134: a benchmark K-dwarf with a compact planetary system  (2610.13200 - Bétrisey et al., 9 Oct 2026) in Section 5.2, “Rotational history”