Evidence for subdominant multipole moments and precession in merging black-hole-binaries from GWTC-2.1

TL;DR

This paper analyzes GWTC-2.1 data to investigate subdominant multipole moments and precession in merging black-hole binaries, finding evidence mainly in specific events and setting limits on higher multipole content.

Contribution

It provides the first systematic evidence assessment for subdominant multipoles and precession in GWTC-2.1 black-hole mergers, highlighting specific events with measurable effects.

Findings

No higher than $ ext{l} = 3$ multipole detected

Marginal evidence for $(3,3)$ multipole in GW190519 extunderscore153544 and GW190929 extunderscore012149

Possible measurable multipole content in GW190521

Abstract

The LIGO--Virgo--KAGRA collaborations (LVK) produced a catalogue containing gravitational-wave (GW) observations from the first half of the third GW observing run (O3a). This catalogue, GWTC-2.1, includes for the first time a number of \emph{exceptional} GW candidates produced from merging black-hole-binaries with unequivocally unequal component masses. Since subdominant multipole moments and spin-induced orbital precession are more likely to leave measurable imprints on the emitted GW from unequal component mass binaries, these general relativistic phenomena may now be measurable. Indeed, both GW190412 and GW190814 have already shown conclusive evidence for subdominant multipole moments. This provides valuable insights into the dynamics of the binary. We calculate the evidence for subdominant multipole moments and spin-induced orbital precession for all merging black-hole-binaries in GWTC-2.1 that were observed during O3a and show that (a) no gravitational-wave candidate has measurable higher order multipole content beyond $\ell = 3$, (b) in addition to the confident subdominant multipole measurements in GW190412 and GW190814, GW190519\_153544 and GW190929\_012149 show marginal evidence for the $(\ell, |m|) = (3, 3)$ subdominant multipole, (c) GW190521 may have measurable subdominant multipole content and (d) GW190412 may show evidence for spin-induced orbital precession.