Resolving white dwarf binaries within globular clusters with LISA

TL;DR

This study assesses LISA's ability to resolve white dwarf binaries in globular clusters from those in the Milky Way disc, finding that sky location and distance measurements can distinguish some clusters, especially those far from the Galactic plane.

Contribution

It demonstrates the potential of LISA to identify and distinguish WD binaries in specific globular clusters based on simulated sky location and distance errors.

Findings

Five GCs can be distinguished by sky location alone.

Ten GCs cannot be distinguished due to overlap with MW disc binaries.

Farther GCs from the Galactic plane are easier to resolve.

Abstract

Context: Globular clusters (GCs) around the Milky Way (MW) are expected to host white dwarf (WD) binaries emitting gravitational waves that could be detectable by LISA. Aims: Our aim is to investigate whether LISA can resolve WD binaries in GCs well enough in terms of sky location and distance that they can be distinguished from binaries in the MW disc. Methods: We used a sample of 20 of the most massive GCs around the MW and simulated LISA's sky location and distance measurement errors for WD binaries in these GCs using the software package GWToolbox. We did this in the context of a model of the LISA-detectable binaries in the MW from the population synthesis code SeBa. Results: We find that for five of the GCs in our sample, binaries in the GC could be easily distinguished from MW disc binaries using the sky location alone; for another five, binaries in the GCs could be distinguished using a combination of LISA's sky location and distance measurements; and for the final ten, binaries in the GCs could not be distinguished from overlapping MW disc binaries. The results depend strongly on the sky locations of the GCs, with GCs far away from the Galactic plane being easy to resolve, while GCs close to the Galactic centre overlap with many MW disc binaries. The most promising GC for finding a WD binary that could be resolved to that GC, based on sky location and GC mass, is 47 Tucanae.