A multi-messenger study of the Milky Way's stellar disc and bulge with LISA, Gaia and LSST

TL;DR

This paper explores how gravitational wave detections of white dwarf binaries by LISA, combined with electromagnetic data, can map the Milky Way's structure and dynamics, enabling multi-messenger astronomy and improved Galactic modeling.

Contribution

It demonstrates that LISA's gravitational wave data can accurately trace the Milky Way's density profiles and disentangle disc structures, advancing multi-messenger Galactic studies.

Findings

LISA will detect ~10^5 DWD binaries across the Galaxy.

DWD density profiles can constrain Galactic scale lengths with few percent errors.

Up to 80 DWDs can be observed via both gravitational waves and electromagnetic signals.

Abstract

The upcoming LISA mission offers the unique opportunity to study the Milky Way through gravitational wave radiation from Galactic binaries. Among the variety of Galactic gravitational wave sources, LISA is expected to individually resolve signals from $\sim 10^5$ ultra-compact double white dwarf (DWD) binaries. DWDs detected by LISA will be distributed across the Galaxy, including regions that are hardly accessible to electromagnetic observations such as the inner part of the Galactic disc, the bulge and beyond. We quantitatively show that the large number of DWD detections will allow us to use these systems as tracers of the Milky Way potential. We demonstrate that density profiles of DWDs detected by LISA may provide constraints on the scale length parameters of the baryonic components that are both accurate and precise, with statistical errors of a few percent to $10$ percent level. Furthermore, the LISA sample is found to be sufficient to disentangle between different (commonly used) disc profiles, by well covering the disc out to sufficiently large radii. Finally, up to $\sim 80$ DWDs can be detected through both electromagnetic and gravitational wave radiation. This enables multi-messenger astronomy with DWD binaries and allows one to extract their physical properties using both probes. We show that fitting the Galactic rotation curve constructed using distances inferred from gravitational waves {\it and} proper motions from optical observations yield a unique and competitive estimate of the bulge mass. Instead robust results for the stellar disc mass are contingent upon knowledge of the Dark Matter content.