Revisiting the relationship of black-hole kicks and multipole asymmetries

Understand

Precession in black-hole binaries is caused by a misalignment between the total spin and the orbital angular momentum.

• The gravitational-wave emission of such systems is anisotropic, which leads to an asymmetry in the $\pm m$ multipoles when decomposed into a spherical harmonic basis.
• This asymmetric emission can impart a kick to the merger remnant black hole as a consequence of linear momentum conservation.
• Despite the astrophysical importance of kicks, multipole asymmetries contribute very little to the overall signal strength and, therefore, the majority of current gravitational-wave models do not include them.