A complete measurement of a black-hole recoil through higher-order gravitational-wave modes

Understand

General relativity predicts that gravitational waves (GWs) carry linear momentum.

• Consequently, the remnant black hole of a black-hole merger can inherit a recoil velocity or ``kick'' of crucial implications in, e.g., black-hole formation scenarios.
• While the kick magnitude is determined by the mass ratio and spins of the source, estimating its direction requires a measurement of the \textit{two orientation angles} of the source.
• While the orbital inclination angle is commonly reported in GW observations, the scientific potential of the azimuthal one has not been exploited to date.