Dynamics of Black Hole Pairs I: Periodic Tables

TL;DR

This paper develops a simplified, quantitative framework to classify and understand the complex three-dimensional orbits of comparable mass, spinning black hole binaries, revealing prevalent zoom-whirl behaviors and implications for gravitational wave signals.

Contribution

It introduces a new taxonomy and simplified equations of motion for black hole binary orbits, clarifying their dynamics and gravitational wave signatures in the strong-field regime.

Findings

Derived simplified equations of motion in a non-orthogonal orbital basis.

Established a complete taxonomy for three-dimensional black hole orbits.

Found that zoom-whirl behavior is common in strong-field binary orbits.

Abstract

Although the orbits of comparable mass, spinning black holes seem to defy simple decoding, we find a means to decipher all such orbits. The dynamics is complicated by extreme perihelion precession compounded by spin-induced precession. We are able to quantitatively define and describe the fully three dimensional motion of comparable mass binaries with one black hole spinning and expose an underlying simplicity. To do so, we untangle the dynamics by capturing the motion in the orbital plane. Our results are twofold: (1) We derive highly simplified equations of motion in a non-orthogonal orbital basis, and (2) we define a complete taxonomy for fully three-dimensional orbits. More than just a naming system, the taxonomy provides unambiguous and quantitative descriptions of the orbits, including a determination of the zoom-whirliness of any given orbit. Through a correspondence with the rationals, we are able to show that zoom-whirl behavior is prevalent in comparable mass binaries in the strong-field regime. A first significant conclusion that can be drawn from this analysis is that all generic orbits in the final stages of inspiral under gravitational radiation losses are characterized by precessing clovers with few leaves and that no orbit will behave like the tightly precessing ellipse of Mercury. The gravitational waveform produced by these low-leaf clovers will reflect the natural harmonics of the orbital basis -- harmonics that, importantly, depend only on radius. The significance for gravitational wave astronomy will depend on the number of windings the pair executes in the strong-field regime and could be more conspicuous for intermediate mass pairs than for stellar mass pairs.