Tidal Spin-up of Black Hole Progenitor Stars

Understand

Gravitational wave observations indicate the existence of merging black holes (BHs) with high spin ($a\gtrsim0.3$), whose formation pathways are still an open question.

• A possible way to form those binaries is through the tidal spin-up of a Wolf-Rayet (WR) star by its BH companion.
• In this work, we investigate this scenario by directly calculating the tidal excitation of oscillation modes in WR star models, determining the tidal spin-up rate, and integrating the coupled spin-orbit evolution for WR-BH binaries.
• We find that for short-period orbits and massive WR stars, the tidal interaction is mostly contributed by standing gravity modes, in contrast to Zahn's model of travelling waves which is frequently assumed in the literature.