Physical calibration of convective overshoot and the mixing length
In plain words
Stellar models describe convection, the boiling motion of hot gas, with a single adjustable length and add extra mixing past the convective boundary by hand. Different calibrations disagree, and the chosen values change derived stellar ages.
Precise statement
Mixing-length theory uses $\alpha_{\mathrm{MLT}}\sim 1.8$ calibrated on the Sun, and convective boundary mixing uses an overshoot extent of about 0.1 to 0.3 pressure scale heights. Determine whether $\alpha_{\mathrm{MLT}}$ is universal across mass, metallicity and evolutionary stage, and determine the overshoot extent and profile as a function of stellar mass, from 3D simulations validated against eclipsing binaries and asteroseismology.
What would settle it
3D convection simulations at realistic stellar parameters yielding a boundary-mixing law that fits eclipsing-binary and asteroseismic constraints across 1 to 10 $M_{\mathrm{sun}}$.
Status in the literature
Eclipsing-binary calibrations suggesting overshoot grows with mass have been disputed as a degeneracy with other model parameters.
See also
- Related Why do red-giant cores rotate far slower than models predict?
- Related Are the oldest stars too old for a Hubble constant of 0.73?
- Related Can stellar transport deplete lithium uniformly by a factor three?
- Related Does the ultimate $\mathrm{Nu} \sim \mathrm{Ra}^{1/2}$ regime exist in Rayleigh-Benard convection?