Testing the no-hair theorem with black hole ringdowns using TIGER

TL;DR

This paper demonstrates that the TIGER model selection scheme can effectively test the no-hair theorem using black hole ringdown signals from the Einstein Telescope, even at large distances and low signal-to-noise ratios, by combining multiple sources.

Contribution

It introduces the application of TIGER to black hole ringdowns for the first time, enabling the detection of deviations from the no-hair theorem with many distant sources.

Findings

Detectable deviations with ~10 sources out to 50 Gpc

TIGER performs well at low signal-to-noise ratios

Effective testing of the no-hair theorem at high redshifts

Abstract

The Einstein Telescope (ET), a proposed third-generation gravitational wave observatory, would enable tests of the no-hair theorem by looking at the characteristic frequencies and damping times of black hole ringdown signals. In previous work it was shown that with a single $500 - 1000\,M_\odot$ black hole at distance $\lesssim 6$ Gpc (or redshift $z \lesssim 1$), deviations of a few percent in the frequencies and damping times of dominant and sub-dominant modes would be within the range of detectability. Given that such sources may be relatively rare, it is of interest to see how well the no-hair theorem can be tested with events at much larger distances and with smaller signal-to-noise ratios, thus accessing a far bigger volume of space and a larger number of sources. We employ a model selection scheme called TIGER (Test Infrastructure for GEneral Relativity), which was originally developed to test general relativity with weak binary coalescence signals that will be seen in second-generation detectors such as Advanced LIGO and Advanced Virgo. TIGER is well-suited for the regime of low signal-to-noise ratio, and information from a population of sources can be combined so as to arrive at a stronger test. By performing a range of simulations using the expected noise power spectral density of Einstein Telescope, we show that with TIGER, similar deviations from the no-hair theorem as considered in previous work will be detectable with great confidence using $\mathcal{O}(10)$ sources distributed uniformly in co-moving volume out to 50 Gpc ($z \lesssim 5$).