Detectability of gravitational higher order modes in the 3G era.

Detection of higher order modes of gravitational waves in third-generation ground-based detectors such as Cosmic Explorer and Einstein Telescope is explored. Assuming an astrophysical population of binary black holes based on events reported in the second gravitational wave catalog by LIGO and Virgo (GWTC-2), we assess the detectability of these higher order modes using a network consisting of three third-generation detectors. We find that the two sub-leading modes ((3,3) and (4,4)) can be detected in around 80\% of the population with a network signal-to-noise ratio of 10 or more, and for nearly 20\% of the sources, all six leading modes will be detectable. Besides, a study concerning the effect of binary's mass ratio and its orbital inclination with the observer's line-of-sight in detecting various modes is presented. For a few selected events of the LIGO-Virgo catalog, we identify the modes that would have been detected if a third-generation detector was operational when these events were recorded. Observing these higher order modes in the 3G era would have a huge impact on the science possible with these detectors ranging from astrophysics and cosmology to testing strong-field gravity.