From simulations of binary black holes to insights into astrophysics and gravitational waves*

The late orbital dynamics of spinning binary black holes remains a fascinating area of research.  Among the notable spin effects observed in supercomputer simulations are the hangup effect which prompts or delays the merger of binary black holes depending on the sign of the spin-orbit coupling, the flip-flop of black hole spins in a binary, passing from aligned to antialigned periods with respect to the orbital angular momentum, the alignment instability (a case of imaginary flip-flop frequencies), and the total flip of the orbital angular momentum, leading to beaconing patterns of gravitational radiation.

Through numerical simulations it was found the large recoils of the final black hole remnant, reaching up to 5000km/s. Accurate modeling of those recoil velocities allows, for instance, to use observational measurements of recoiling supermassive quasars, like 3C 186, to infer the masses and spins of the progenitor binary.

Fitting formulas relating initial binary parameters (individual masses and spins) to the final merger properties (peak amplitudes and frequency, and final remnant mass and spin) are of interest for applications to astrophysical and gravitational wave observations. 

Finally, catalogs of black hole merger waveforms can be used to accurately determine the binary's parameters, directly from the observed gravitational waves.