Studying spin tilts in the binary black hole population, just for kicks

Observations of galactic compact objects, like neutron stars and black holes, suggest that some stellar remnants receive a "kick" during the core-collapse of their massive progenitors. In a binary, this kick may misalign the spin of the stellar remnant and its orbit. However, the mechanism for momentum transfer from the collapsing star to the proto-compact object core remains uncertain. Meanwhile, the latest LIGO-Virgo-Kagra catalog of binary black hole mergers is not inconsistent with the distribution peaking at tilts as high as 80 degrees. This is in tension with the canonical assumption that compact binaries forming in isolated environments should tend to have essentially zero misalignment. Here, we use Monte Carlo simulations to study whether any combination of standard assumptions about isolated binary evolution can produce peaks in the distribution of spin-orbit misalignments away from zero. We also investigate which non-standard assumptions—such as lack of spin alignment between supernovae, spin tossing, or off-axis kicks—can reproduce the misalignment distribution inferred via gravitational waves.