Understand
If binary black holes form following the successive core collapses of sufficiently massive binary stars, precessional dynamics may align their spins $\mathbf S_1$ and $\mathbf S_2$ and the orbital angular momentum $\mathbf L$ into a plane in which they jointly precess about the total angular momentum $\mathbf J$.
- These spin orientations are known as spin-orbit resonances since $\mathbf S_1$, $\mathbf S_2$, and $\mathbf L$ all precess at the same frequency to maintain their planar configuration.
- Two families of such spin-orbit resonances exist, alike in dignity but differentiated by whether the components of the two spins in the orbital plane are either aligned or antialigned.
- The fraction of binary black holes in each family is determined by the stellar evolution of their progenitors, so if gravitational-wave detectors could measure this fraction they could provide important insights into astrophysical formation scenarios for binary black holes.
Reading the bibliography…