Challenges and Opportunities for time-delay cosmography with multi-messenger gravitational lensing

TL;DR

This paper explores the potential of using gravitational wave signals in time-delay cosmography, comparing it to electromagnetic methods, and discusses the challenges and advantages of this new approach for constraining cosmological parameters.

Contribution

It provides a comparative analysis of GW and EM signals for time-delay cosmography and identifies key challenges and opportunities in adopting GW signals for cosmological measurements.

Findings

GW signals can potentially improve time-delay measurements.

Astrometric precision is a critical challenge.

Near-perfect GW time-delay measurements could significantly impact cosmology.

Abstract

Strong gravitational lensing of variable sources, such as quasars or supernovae, can be used to constrain cosmological parameters through a technique known as "time-delay cosmography''. Competitive constraints on the Hubble constant have been achieved with electromagnetic observations of lensed quasars and lensed supernovae. Gravitational wave (GW) astronomy may open up a new channel for time-delay cosmography with GW signal replacing the electromagnetic (EM) one. We highlight the similarities of using GW signals to be applied to time-delay cosmography compared to EM signal. We then discuss key differences between GW and EM signals and their resulting advantages and inconveniences from the angle of the current state-of-the-art using quasars and lensed supernovae for time-delay cosmography. We identify the astrometric precision requirement of the images as a key challenge to overcome and highlight the potentially significant impact that near-perfect time-delay measurements of lensed GWs can bring to the table.