Unveiling the spectrum of inspiralling binary black holes

TL;DR

This paper introduces a novel method for detecting higher-multipole gravitational wave signals from binary black hole mergers by stacking data from multiple events, significantly improving detection prospects.

Contribution

The authors develop a new stacking technique that enhances the detection of sub-dominant gravitational wave modes across multiple events, enabling their observation with current detectors.

Findings

Stacking multiple events increases the signal-to-noise ratio for higher-multipole modes.

Monte Carlo simulations suggest ~100 events can yield 95% detection probability.

Analysis of O1 and O2 data demonstrates the method's practical applicability.

Abstract

The higher-multipoles of gravitational wave signals from coalescing compact binaries play a vital role in the accurate reconstruction of source properties, bringing about a deeper and nuanced understanding of fundamental physics and astrophysics. Their effect is most pronounced in systems with asymmetric masses having an orbital geometry that is not face-on. The detection of higher-multipoles of GW signals from any single, isolated merger event is challenging, as there is much less power in comparison to the dominant quadrupole mode. In this paper, we present a new method for their detection by combining multiple events observed in interferometric gravitational wave detectors. Sub-dominant modes present in (the inspiral part of) the signal from separate events are stacked using time-frequency spectrogram of the data. We demonstrate that this procedure enhances the signal-to-noise ratio of the higher-multipole components and thereby leads to increased chances of their detection. From Monte-Carlo simulations, we estimate that a combination of $\sim 100$ events observed in two-detector coincidence can lead to the detection of the higher-multipole components with a $\geq$ 95\% detection probability. The advanced-LIGO detectors are expected to record these many binary black hole merger events within a month of operation at design sensitivity. We also present results from the analysis of data from O1 and O2 science runs containing previously detected events using our new method.