Polar Alignment in Warped Circumbinary Discs Accelerates Binary Shrinkage by 10-20x

The simulations employ a locally isothermal alpha-disc with H/r equal to viscous alpha of 0.1 and fixed Keplerian binary orbits. Discs with inclination exceeding the eccentricity-dependent critical value drive their inner regions polar, redirecting torques to shrink the binary orbit rather than merely reorient it. At eccentricity 0.6, the polar transition acts as a single transient that either enhances or suppresses accretion depending on exact inclination, while misalignment suppresses the usual eccentricity pumping seen in coplanar cases below roughly 15 degrees.

These outcomes revise expectations for circumbinary planet formation because rapid polar settling means most observed misaligned discs around stellar binaries are already near their final state, not transitional. The vanishing of the 4.5-orbit accretion modulation during strong warps provides a potential observational signature for misaligned massive black-hole binaries. The work connects to broader patterns in exoplanet demographics where misaligned binaries may produce lower-eccentricity systems entering the gravitational-wave regime than coplanar models predict.

Future multi-scale simulations coupling disc evolution to planet migration and binary inspiral will test whether polar channels dominate the observed population of close binaries. High-resolution ALMA and JWST observations of systems like HD 98800 can directly check the predicted rapid polar alignment timescale.

The main limitation remains the fixed-orbit assumption and limited parameter space; self-consistent binary evolution over longer timescales would strengthen causal claims about shrinkage rates.