Stellar interiors: transport and mixing

3 problems

• Why are M dwarfs larger and cooler than models predict?

  Contested

  Small red stars called M dwarfs, measured precisely in eclipsing pairs, are a few percent larger and cooler than models say. Strong magnetic fields or dark starspots may be the cause, but this is not established.

• Physical calibration of convective overshoot and the mixing length

  Contested

  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.

• Why do red-giant cores rotate far slower than models predict?

  Open

  Star vibrations measured by the Kepler telescope show that the cores of red giant stars spin slowly. Standard models, which let the core contract and spin up, predict cores that spin about ten times faster or more.