Constraining the nature of dark compact objects with spin-induced octupole moment measurement

TL;DR

This paper develops a Bayesian framework to measure the spin-induced octupole moment of compact objects using gravitational wave data, enabling tests of their nature against black hole predictions.

Contribution

It introduces the first full Bayesian analysis method to constrain the spin-induced octupole moment from gravitational wave observations.

Findings

LIGO and Virgo can constrain octupole moments for spins ~0.8.

Simultaneous measurement of quadrupole and octupole moments is feasible.

First constraints on octupole moments from real GW events.

Abstract

Various theoretical models predict the existence of exotic compact objects that can mimic the properties of black holes (BHs). Gravitational waves (GWs) from the mergers of compact objects have the potential to distinguish between exotic compact objects and BHs. The measurement of spin-induced multipole moments of compact objects in binaries provides a unique way to test the nature of compact objects. The observations of GWs by LIGO and Virgo have already put constraints on the spin-induced quadrupole moment, the leading order spin-induced moment. In this work, we develop a Bayesian framework to measure the spin-induced octupole moment, the next-to-leading order spin-induced moment. The precise measurement of the spin-induced octupole moment will allow us to test its consistency with that of Kerr BHs in general relativity and constrain the allowed parameter space for non-BH compact objects. For various simulated compact object binaries, we explore the ability of the LIGO and Virgo detector network to constrain the spin-induced octupole moment of compact objects. We find that LIGO and Virgo at design sensitivity can constrain the symmetric combination of component spin-induced octupole moments of binary for dimensionless spin magnitudes $\sim 0.8$. Further, we study the possibility of simultaneously measuring the spin-induced quadrupole and octupole moments. Finally, we perform this test on selected GW events reported in the third GW catalog. These are the first constraints on spin-induced octupole moment using full Bayesian analysis.