Resolving white dwarf binaries within globular clusters with LISA

¹ Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, 6500 GL, Nijmegen, The Netherlands
² Leiden Observatory, Leiden University, Einsteinweg 55, 2333 CC, Leiden, The Netherlands
³ Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand
⁴ SRON, Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA Leiden, The Netherlands
⁵ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁶ Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
⁷ University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100049, China

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 14 August 2025
Accepted: 16 November 2025

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 has the capacity to 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 with respect to the potential of locating a WD binary that could be resolved to that specific GC (based on sky location and GC mass) is 47 Tucanae.