Multi-mode black hole spectroscopy

TL;DR

Future gravitational wave detectors like LISA will enable detailed black hole spectroscopy by detecting multiple quasinormal modes, allowing tests of the Kerr black hole hypothesis at various redshifts.

Contribution

This paper quantifies the detectability of multiple quasinormal modes from black hole mergers across different redshifts for future detectors.

Findings

LISA can detect many quasinormal modes from black hole mergers.

Current numerical relativity simulations may be insufficient for analyzing all detected modes.

Detectability depends on the intrinsic parameters of the merging binary.

Abstract

The first two LIGO/Virgo observing runs have detected several black hole binary mergers. One of the most exciting prospects of future observing runs is the possibility to identify the remnants of these mergers as Kerr black holes by measuring their (complex) quasinormal mode frequencies. This idea - similar to the identification of atomic elements through their spectral lines - is sometimes called "black hole spectroscopy". Third-generation Earth-based detectors and the space-based interferometer LISA could measure multiple spectral lines from different multipolar components of the radiation, and therefore provide qualitatively better tests of the Kerr hypothesis. In this paper we quantify the redshift out to which the various modes would be detectable (or, conversely, the number of detectable modes at any given redshift) as a function of the intrinsic parameters of the merging binary. LISA could detect so many modes that current numerical relativity simulations would not be sufficient to extract all available science from the data.