Connecting stellar binary evolution with binary black-hole spin precession

Binary black holes (BBHs) can form from the collapsed cores of isolated high-mass binary stars. The masses and spins of these BBHs are determined by the interplay of phenomena such as tides, winds, accretion, common-envelope evolution (CEE), natal kicks, and stellar core-envelope coupling. The gravitational waves (GWs) emitted during the mergers of BBHs depend on their masses and spins and can thus constrain these phenomena. We present a simplified model of stellar binary evolution to identify regions of the parameter space that produce BBHs with large spins misaligned with their orbital angular momentum. In Scenario A (B) of our model, stable mass transfer (SMT) occurs after Roche-lobe overflow (RLOF) of the more (less) massive star, while CEE follows RLOF of the less (more) massive star. Each scenario is further divided into Pathways 1 and 2 depending on whether the core of the more massive star collapses before or after RLOF of the less massive star. If the stellar cores are weakly coupled to their envelopes, highly spinning BBHs can be produced if natal spins greater than 10% of the breakup value are preserved during the Wolf-Rayet (WR) stage. BBHs can also acquire large spins by tidal synchronization during the WR stage in Scenario A or accretion onto the initially more massive star in Scenario B. BBH spins can become highly misaligned if the natal kicks are comparable to the orbital velocity which is more easily achieved in Pathway A1 where the first collapse event precedes CEE. These BBHs with large, misaligned spins will likely experience spin precession through the LIGO/Virgo sensitivity band. We present a taxonomy for modelling BBH spin precession in the post-Newtonian regime utilizing a multi-timescale analysis that yields 5 independent parameters which describe the evolution: spin-orbit misalignments cause the orbital angular momentum to precess in a cone about the total angular momentum, while large spin magnitudes induce nutations of the orbital angular momentum. We explore how these 5 parameters depend on isotropically distributed spin misalignments and we explore the impact of the various astrophysical phenomena in our model of binary evolution.