Tides in Massive Binaries: Numerical Solutions and Semianalytical Comparisons

Abstract We present a systematic comparison between the tidal secular evolution timescales predicted by the direct numerical method and those given by the commonly used semianalytic prescriptions implemented in 1D hydrostatic binary evolution codes. Our study focuses on binary systems with intermediate- to high-mass primaries ( M 1 = 5–50 M ⊙ ), companion masses between 1.4 M ⊙ and 10 M ⊙ , and orbital periods ranging from 0.5–50 days. Before mass transfer, both approaches predict synchronization and orbital decay timescales that agree within ∼2 orders of magnitude and typically exceed the stellar main-sequence lifetime, implying negligible tidal impact on secular orbital evolution. However, the implied dissipation channels differ, and the differences become more pronounced once mass transfer begins. To test the theoretical predictions against observations, we apply both approaches to the well-characterized PSR J0045–7319 system, which has an orbital decay timescale of 0.5 Myr. The numerical solution reveals strong resonances with internal gravity waves, bringing the predicted orbital period change rate close to the observed value. In contrast, the semianalytic prescriptions predict orbital decay timescales longer than the Hubble time. These results suggest that for population studies, modestly calibrated parameterized equations may suffice, but for individual systems, reliable interpretation requires direct numerical approaches.