Spin Flips and Precession in Black-Hole-Binary Mergers

TL;DR

This study uses advanced numerical simulations to analyze the precession and spin-flip phenomena in merging black-hole binaries with misaligned spins, providing new insights into spin dynamics during mergers.

Contribution

It introduces a novel technique to measure spin orientation and track precession, confirming the spin-flip phenomenon during black-hole mergers for the first time.

Findings

Spins precess significantly during merger, with angles up to 151 degrees.

The remnant black hole's spin can flip by about 72 degrees.

Orbital plane precession frequency matches orbital frequency.

Abstract

We use the `moving puncture' approach to perform fully non-linear evolutions of spinning quasi-circular black-hole binaries with individual spins not aligned with the orbital angular momentum. We evolve configurations with the individual spins (parallel and equal in magnitude) pointing in the orbital plane and 45-degrees above the orbital plane. We introduce a technique to measure the spin direction and track the precession of the spin during the merger, as well as measure the spin flip in the remnant horizon. The former configuration completes 1.75 orbits before merging, with the spin precessing by 98-degrees and the final remnant horizon spin flipped by ~72-degrees with respect to the component spins. The latter configuration completes 2.25 orbits, with the spins precessing by 151-degrees and the final remnant horizon spin flipped ~34-degrees with respect to the component spins. These simulations show for the first time how the spins are reoriented during the final stage of binary black hole mergers verifying the hypothesis of the spin-flip phenomenon. We also compute the track of the holes before merger and observe a precession of the orbital plane with frequency similar to the orbital frequency and amplitude increasing with time.