**Date:**04/30/2021**Event:**Conference: Gravitational scattering, inspiral, and radiation**Location:**Galileo Galilei Institute, Italy

## Abstract

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, large recoils of the final black hole remnant, reaching up to 5000km/s, 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.

Also catalogs of black hole merger waveforms can be used to accurately determine the binary's parameters, directly from the observed gravitational waves by directly applying them to O1/O2 LIGO/Virgo observations. 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.

The most challenging small mass ratio binaries has been recently explored as a sequence of small mass ratios based on a detailed convergence study of the q=m1/m2=1/15 nonspinning case. We applied additional mesh refinement levels around the smaller hole horizon to reach successively the q=1/32, q=1/64, and q=1/128 cases, reaching to a 128:1 binary that displays 13 orbits before merger. We computed the remnant properties of the merger: final mass, spin, and recoil velocity, finding precise consistency between horizon and radiation measures. We also compute the gravitational waveforms: their peak frequency, amplitude, and luminosity. We compare those values with predictions of the corresponding phenomenological formulas, reproducing the particle limit within 2%.