Stable Mass Transfer Produces Broad Black Hole Spin Distribution in Isolated Binaries

The arXiv preprint models tidally excited oscillation modes in progenitors undergoing stable mass transfer. Case A transfer allows super-synchronization before detachment, while partial stripping in case B leaves envelopes that sustain strong tides. When both case A and AB occur, spins drop to negligible levels. The calculations tie spin outcomes directly to initial mass ratio and orbital period, predicting an anti-correlation between spin and mass ratio.

This pattern matches the moderate spin and high mass ratio seen in GW190412. The work draws on prior binary population synthesis and LIGO spin measurements but adds explicit mode solving absent from earlier prescriptions. It implies that isolated-channel events can occupy the same spin range previously attributed to dynamical formation.

Limitations include omission of nonlinear tides, case C transfer, and L2 outflows. Future incorporation of these processes and direct comparison against the full O4 catalog will test whether the predicted anti-correlation holds at higher significance.

LIGO-Virgo-KAGRA is expected to add dozens of events with measurable spins by late 2026, providing the first statistical test of the mass-ratio-spin relation.