A system of two black holes emits gravitational waves as the objects spiral around each other. It is well known that this radiation oscillates predominantly at twice the orbital frequency. However, other harmonic frequencies are also present in the signal. In the past years, significant progress was made in including such higher harmonics in theoretical gravitational waveform models of merging binaries, which eventually aided the first unambiguous detections of higher harmonics in the signals GW190412 and GW190814. In this talk, I will discuss the importance of higher harmonics when identifying the source properties of a gravitational wave signal. Beyond information about the source's orientation, I will demonstrate that higher harmonics can be crucial in identifying relativistic spin precession, constraining the remnant's recoil or testing General Relativity.
For additional information, please see https://www.aei.mpg.de/person/51192/2784