Precessional Instability in Binary Black Holes with Aligned Spins

Area of Science:

• Astrophysical relativity
• Gravitational wave astronomy
• Black hole physics

Background:

• Binary black holes on quasicircular orbits with aligned spins are standard models in relativity.
• Symmetry ensures these configurations are equilibrium solutions to spin-precession equations.

Purpose of the Study:

• To investigate the stability of binary black hole spin configurations.
• To identify conditions under which aligned and anti-aligned spins become unstable.

Main Methods:

• Analysis of spin-precession equations for binary black holes.
• Application of recently developed analytical techniques to characterize spin precession.
• Identification of specific binary separation ranges for instability.

Main Results:

• Identified an instability in binary black hole configurations where the higher-mass black hole spin is aligned and the lower-mass black hole spin is anti-aligned.
• This instability leads to large spin misalignment at specific binary separations.
• The instability occurs for a broad range of spin magnitudes and mass ratios, even near merger.

Conclusions:

• The identified spin instability challenges assumptions of astrophysical spin alignment.
• This instability provides a mechanism for significant spin precession before black hole merger.
• It impacts both gravitational-wave and electromagnetic signatures of merging binary black holes.