Spin-Orbit Misalignments in Black Hole X-ray Binaries

A spin-orbit misalignment refers to the directional mismatch between the spin and orbital angular momenta of a black hole in a binary system. Spin-orbit misalignments in X-ray binaries are likely more common than previously appreciated, but are difficult to measure precisely. Presumably, the misalignment mechanism is an asymmetric core-collapse giving the natal black hole a ‘kick’ that reorients the binary orbit. In this talk, we demonstrate a method to validate binary evolution models, by using observational constraints of individual X-ray binaries with extreme misalignments. Our results raise concerns about the unvalidated prescriptions for common envelope evolution and mass transfer that binary evolution models adopt, and/or the assumption that the jet axis traces the black hole spin axis on large scales. Our methodology can be applied to the growing list of X-ray binary systems with spin-orbit misalignment constraints, and offers a new way to validate the binary evolution models now routinely used in studies related to compact object mergers.