Discovering the Cosmic Evolution of Supermassive Black Holes using Nano-Hertz Gravitational Waves and Galaxy Surveys

TL;DR

This paper proposes a novel method to study the evolution of supermassive black holes across cosmic time by cross-correlating nano-Hertz gravitational wave signals with galaxy surveys, enabling new insights beyond existing techniques.

Contribution

It introduces the first theoretical prediction of a unique signature in the angular cross-correlation power spectrum between nHz gravitational waves and galaxy density, facilitating observational studies of SMBH evolution.

Findings

Potential to measure SMBH evolution with high confidence using upcoming observatories.

Cross-correlation signal detectable with a signal-to-noise ratio above five.

New observational window surpassing current techniques.

Abstract

The formation and evolution of supermassive black holes (SMBHs) in the Universe remains an open question in cosmology. We show for the first time that the evolution of SMBHs with redshift leads to a unique signature on the angular cross-correlation power spectrum between the multi-frequency nano-hertz (nHz) stochastic gravitational wave (SGWB) and the galaxy density in the Universe. By using galaxy catalogs from the upcoming Rubin LSST Observatory in synergy with the nHz SGWB signal accessible from the Square Kilometer Array, we can measure this signal with a signal-to-noise ratio above five, thereby opening a new observational window to the cosmic evolution of SMBHs across redshift. This discovery space that can be opened by the cross-correlation of the nHz SGWB will not be possible by any other currently known techniques.