Abstract
Gravitational-wave observations of extreme mass ratio inspirals (EMRIs) offer the opportunity to probe the environments of active galactic nuclei (AGN) through the torques that accretion disks induce on the binary. Within a Bayesian framework, we study how well such environmental effects can be measured using gravitational wave observations from the Laser Interferometer Space Antenna (LISA). We focus on the torque induced by planetary-type migration on quasicircular inspirals and use different prescriptions for geometrically thin and radiatively efficient disks. We find that LISA could detect migration for a wide range of disk viscosities and accretion rates, for both and disk prescriptions. For a typical EMRI with masses , we find that LISA could distinguish between migration in and disks and measure the torque amplitude with relative precision. Provided an accurate torque model, we also show how to turn gravitational-wave measurements of the torque into constraints on the disk properties. Furthermore, we show that, if an electromagnetic counterpart is identified, the multimessenger observations of the AGN EMRI system will yield direct measurements of the disk viscosity. Finally, we investigate the impact of neglecting environmental effects in the analysis of the gravitational-wave signal, finding biases in the primary mass and spin, and showing that ignoring such effects can lead to false detection of a deviation from general relativity. This work demonstrates the scientific potential of gravitational observations as probes of accretion-disk physics, accessible so far through electromagnetic observations only.
- Received 19 August 2022
- Revised 10 April 2023
- Accepted 1 May 2023
DOI:https://doi.org/10.1103/PhysRevX.13.021035
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.
Published by the American Physical Society
Physics Subject Headings (PhySH)
synopsis
synopsisAccretion Explored through Gravitational Waves
Published 15 June 2023
Future space-based gravitational-wave detectors could probe the physics of accretion disks surrounding massive black holes.
See more in Physics
Popular Summary
The rich phenomenology of accretion disks—ubiquitous in galaxies, black holes, and stars—is difficult to capture with first-principles models. Traditional observations of their electromagnetic emission are also limited. But any masses embedded in an accretion disk can be considerably perturbed by the environment, leaving a detectable imprint in the emitted gravitational waves. We show that one can infer properties of the accretion disk from gravitational-wave observations of compact objects spiraling into accreting black holes. Thus, future space-borne gravitational-wave detectors have the potential to probe accretion-disk physics beyond what is achievable through light and modeling.
After identifying the disks that gravitational-wave observations could realistically probe, we show how to capture the disk’s influence through a phenomenological model, performing the first realistic parameter estimation for this type of source. Our model can discriminate between accretion-disk prescriptions and even be used to infer disk properties, such as viscosity, that are currently inaccessible to electromagnetic observations. We highlight that neglecting the presence of the disk can be detrimental when testing Einstein’s theory of gravity with gravitational waves.
Gravitational-wave observations have already been used to explore the fundamental nature of gravity and black holes. Future detectors will open the possibility of exploring accretion as well. This should motivate intense modeling of compact objects’ interactions with accretion-disk environments.
