Pathways for producing binary black holes with large misaligned spins in the isolated formation channel

TL;DR

This paper models binary stellar evolution to identify pathways that produce binary black holes with large, misaligned spins, highlighting the roles of stellar processes, natal kicks, and specific evolutionary scenarios.

Contribution

It introduces a simplified model of binary evolution that delineates pathways leading to highly spinning, misaligned binary black holes, emphasizing the impact of stellar coupling, kicks, and accretion.

Findings

Highly spinning BBHs can form with weak core-envelope coupling.

Large spin misalignments occur if natal kicks are comparable to orbital velocity.

Specific evolutionary pathways favor the formation of misaligned, high-spin BBHs.

Abstract

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 complicated interplay of phenomena such as tides, winds, accretion, common-envelope evolution (CEE), supernova natal kicks, and stellar core-envelope coupling. The gravitational waves emitted during the mergers of BBHs depend on their masses and spins and can thus constrain these phenomena. We present a simplified model of binary stellar evolution and 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, respectively. If the stellar cores are coupled weakly to their envelopes, highly spinning BBHs can be produced if natal spins greater than $10\%$ of the breakup value are inherited from the stellar progenitors. BBHs can alternatively acquire large spins by tidal synchronization during the Wolf-Rayet stage in Scenario A or by accretion onto the initially more massive star during SMT in Scenario B. BBH spins can be highly misaligned if the kicks are comparable to the orbital velocity, which is more easily achieved in Pathway A1 where the kick of the more massive star precedes CEE.