Probing AGN Disks Density Profiles through Gravitational Wave Observations

TL;DR

This paper proposes a method to measure the density profiles of gas disks around active galactic nuclei by analyzing gravitational wave signals from inspiraling black hole binaries, enabling insights into galactic centers.

Contribution

It introduces a novel approach to determine AGN disk density profiles using gravitational wave observations of embedded binary black holes, achieving high precision in density measurements.

Findings

Density profiles can be inferred with errors below 2×10⁻¹¹ g/cm³.

Gravitational wave signals encode information about the surrounding gas density.

Multi-year space-based GW observations can reveal detailed AGN disk structures.

Abstract

Massive black holes surrounded by a gaseous disk have been a prevailing model to explain a wide spectrum of astrophysical phenomena related to active galactic nucle (AGNs). However, direct and precise measurements of the disk density profiles remain elusive for current telescopes. In this work, we demonstrate that it is possible to pinpoint the gas density if an inspiralling stellar mass binary black hole is embedded in the AGN disk. Furthermore, if the barycenter of the pair follows an eccentric orbit around an AGN, then space-borne gravitational wave detectors can measure the density of the surrounding disk with multi-year observations by tracking the gravitational wave evolution. The error between the inferred density profile and the injected truth can be constrained to below $2\times10^{-11}\rm g/cm^3$. Our work opens up an exciting new channel to investigate the very center of galaxies, where disk gas density distributions $\rho(r)$ can be recovered by analyzing time-dependent environmental imprints in gravitational waveforms.